heritage

Article
Conservation of the Built Heritage: Pilot Site
Approach to Design a Sustainable Process
Davide Gulotta *,† and Lucia Toniolo †
Dipartimento di Chimica, Materiali e Ingegneria Chimica “Giulio Natta”, Politecnico di Milano, Piazza
Leonardo da Vinci 32, 20133 Milan, Italy; lucia.toniolo@polimi.it
* Correspondence: davide.gulotta@polimi.it
† These authors contributed equally to this work.




Received: 15 February 2019; Accepted: 4 March 2019; Published: 8 March 2019


Abstract: The conservation project of built heritage is a complex process, dealing with an extremely
heterogeneous range of elements and different substrates with a large variety of conservation
conditions. In recent years, its sustainability has become a relevant issue, due to the general limitation
of resources and unique features of cultural heritage assets. The conservation project, therefore,
requires a thorough knowledge of the specific characteristics of the site, a reliable evaluation of the
treatment’s efficacy and durability, and efficient control of procedures and timing of the site during
the conservation activities. A suitable approach to design the intervention is the implementation of
a pilot site for the knowledge of surfaces and structures, and for the testing of different operative
procedures. This approach needs the collaborative work of a multidisciplinary team coordinated by
the project manager. This paper reports on the design of the conservation project of the Renaissance
façade of the Monza cathedral, with the development of a pilot site as a relevant example of a
complex surface. The three-phase process—preliminary knowledge, testing and implementation of
the treatment methodologies, and scale-up to the general conservation project—is described and
discussed with significant reference to real data from the case study.

Keywords: stone deterioration; condition survey; pilot site; conservation treatments; onsite testing;
sustainable conservation; conservation project

1. Introduction
The surfaces of architectural heritage are unique and irreplaceable landmarks that contribute to the
definition of the identity of cities and communities. In particular, the role of historical architecture as an
“expression of the richness and diversity of Europe’s cultural heritage” has been clearly stated by the
Council of Europe [1]. Since its early stages, the long-lasting and fertile debate on the conservation of
built heritage has emphasized the inherent stratification of historical, aesthetic, and technological values
characterizing buildings and sites of cultural significance [2]. All over the world, the preservation
of built heritage is actively pursued through conservation strategies for its transmission to future
generations and the protection of its authenticity [3,4]. Nevertheless, the conservation project of
historical buildings is a complex and expensive process, dealing with a wide range of architectural
elements, made of a variety of different materials, with quite a large extension. In recent years, the
sustainability of this process has become more and more important due to the general limitation of
resources. This requires a reassessment of the intervention and maintenance strategies by the main
actors involved in the safeguard, decision-making, management, and planning phases of conservation
towards more highly efficient approaches. Following this direction, efforts have been made to apply the
well-established tools of sustainability to the environmental, economic, and social aspects of cultural
heritage conservation [5].

Heritage 2019, 2, 797–812; doi:10.3390/heritage2010052 www.mdpi.com/journal/heritage

Heritage 2019, 2 798

Under the operational point of view of the heritage conservation, sustainability is a multi-faceted
objective that can be addressed following several directions, including the selection of cost-effective
restoration materials to meet the specific site’s requirements and constraints [6]; the use of procedures
that are respectful of both the environment and the operators; the definition of methodological
approaches to reduce the risk of materials and treatments incompatibility [7,8]; the implementation
of strategies to grant adequate durability of the conservation solutions, also considering the current
global climate change scenario [9,10]; optimized scheduling of the conservation activity, and managing
of the financial resources.
Monumental, historical, and modern architecture, as well as the diffused built heritage, face
prolonged exposure to outdoor environments that can be extremely challenging for the substrates
especially in polluted urban atmospheres. Severe damages affect historical surfaces [11,12], posing a
serious risk of losing architectural elements and details that characterize building traditions and skills
across the centuries. The sequence of restoration and maintenance activities usually carried out during
the lifetime of buildings and sites further increases the complexity. Restoration treatments indeed
substantially alter the equilibrium of the materials at work with the objective of improving the overall
conservative conditions. The risk of possible incompatibilities with respect to the historic substrates
can be minimized, but not completely excluded [7].
The project of conservation should be based on a thorough knowledge of materials and their
conditions, achieved through a careful diagnostic examination of the different architectural elements.
The diagnostic results allow for the setup of adequate guidelines for the different conservation
phases—cleaning, consolidation, gluing, sealing and re-jointing, and protection [13]. Nevertheless,
these guidelines alone are not sufficient to implement executive planning for a satisfactory intervention,
which should also rely on: the thorough knowledge of the specific features of the site (environmental
and microclimatic conditions) [14]; the reliable evaluation of the treatment materials and methodologies
on site [15–17]; the efficient control during the execution of the conservation activities; the assessment
and monitoring of the restoration results, to understand the evolution of the treated surfaces [18–20]
and to allow the early detection of any incompatibility issue.
To meet these requirements, the project for the conservation of the built heritage should be founded
on a solid knowledge basis, which exploits all the possible historical sources and is complemented by
a multidisciplinary diagnostic. The decision-making process leading to the definition of the operative
steps, the specific methodologies, and the treatment procedures will then follow. The basic operational
steps performed during the intervention generally include a preconsolidation of the mechanically
weakened substrates to minimize the risk of loss of historic materials during the subsequent operations;
cleaning procedures for the removal of all the deposits and reactive materials potentially harmful
towards the substrates; re-attachment, integration, and sealing to restore the surface continuity;
consolidation treatments to improve the mechanical cohesion; and, finally, surface protection to provide
water repellency with the aim of mitigating the overall damaging impact promoted by environmental
water. A close collaboration between architects, conservators, and conservation scientists is necessary
to meet the conservation goals and, ultimately, to contribute to the overall sustainability of the process.
Good practice in conservation recommends the preliminary testing of the restoration materials and
methodologies in the lab and to base any decision on previously acquired experience. This is a cautious
and widely recognized strategy, for which extensive data are available in the scientific literature
describing the application of many different materials and products for cleaning, consolidation,
and protection procedures, tested and assessed through standardized protocols in controlled lab
conditions [21–26]. At the same time, only a few experiences of onsite testing and long term
monitoring of conservation treatments are reported. Even if pilot conservation sites have been
implemented to address specific conservation issues, it is still difficult to find comprehensive published
results [15,27–30].
With respect to the traditional approach to the conservation project, the pilot site allows for
testing and comparing a wider range of potential solutions in the real exposure conditions on
Heritage 2019, 2 799

deteriorated surfaces, as well as monitoring the treatments results over a reasonable period of time
after the application, thanks to the collaboration between conservation scientists and conservators.
The laboratory characterization of reference fresh material also contributes to the overall assessment.
The expected outcome is that the most promising procedures can be more precisely identified and
further tuned to improve the overall effectiveness and sustainability, optimizing parameters such as
application methods, concentration, and times. This, in turn, will allow a highly accurate evaluation of
timing and calculation of costs by the executive conservation project team.
This work describes the experience gathered in the context of the project for the preservation
of an important Renaissance façade that can be taken as a relevant example of the above-mentioned
sustainable approach to the conservation of built heritage.

2. The Case Study: The Façade of the Monza Cathedral

The Monza cathedral (Italy) is a masterpiece of Northern Italy architecture that was re-founded
on a pre-existing site at the beginning of the 14th Century and then progressively modified.
The construction works of the façade, in particular, started between 1300 and 1345, but a major
change in the overall design was necessary after the extension of the interiors. As a result, the façade
was enlarged, and its height increased. The current configuration can be attributed to the activity of
Matteo da Campione, starting from the second half of the 14th Century [31]. The final design of the
façade is based on a five-field scheme (Figure 1a). The central field corresponds to the main aisle and is
decorated by a large rose-window, the lateral ones correspond to the side naves, and the external ones
to the side chapels. The crowning elements of the façade and the spires belong to a later stage of the
construction, as they were concluded only at the beginning of the 20th Century. A wide range of local
stones was employed for the cladding and the architectural and decorative elements. Originally, the
façade was cladded with alternated rows of Varenna stone slabs (a local black limestone) and white
slabs of marble. These materials proved to be not adequately durable, and after a first restoration
during the 17th Century, the stone slabs were extensively dismantled and substituted during the early
20th Century restoration. In particular, the black Varenna slabs were completely replaced by Oira stone,
a much more resistant metamorphic lithotype (serpentinite), whereas the white ones were cleaned and
polished or substituted, depending on their state of conservation. No other complete interventions on
the façade have been documented since then, besides the cleaning and some local consolidation of the
central portion around 1980 [31].
After at least a century of outdoor exposure, the state of conservation of the stone surfaces in
2016, at the beginning of the pilot conservation activity, was particularly compromised. Natural
environmental factors and anthropogenic pollutants differently affected the stone surfaces according to
the exposure conditions and the inherent compositional and microstructural features of the substrates.
As a result, the type and magnitude of the decay observed ranged widely from rather mild color
alteration of the most durable stones to black crust formation and massive granular disintegration
of the highly reactive ones. It has to be considered that the city of Monza is located in the Po Valley,
in a densely populated area not far from Milan. From the early 20th Century, the city has almost
triplicated its residential populations. In the past, this area was characterized by particularly severe
conditions due to the relevant concentrations of solid and gas pollutants. Nowadays, despite an overall
improvement of the air quality, the concentrations of particulate matter (especially belonging to the
PM10 fraction), NOx , and ozone remain critical [32].
After the preliminary examination of the stone surfaces of the façade, the pilot site area was
identified in the mid-left field of the façade (from the ground level to the top of the spire) (Figure 1).
This area was indeed highly representative of the most relevant surface features, as for type and state of
conservation of the building materials, stone finishings, surface orientations, geometry, and exposure
conditions of the different architectural elements (i.e., sheltered, partially or completely exposed to the
action of the rain and of the rain runoff). Within the pilot site area were vast portions of the marble
and serpentinite slabs of the cladding, a double- and a triple-arched window with remnants of colored
Heritage 2019, 2 800

patinas, a small rose window framed by a detailed decoration of stone sculpted elements, the crowning
Heritage 2019, 2 FOR PEER REVIEW 4
elements heavily exposed to precipitations, and one of the main spires hosting the large statue of the
queenscaffolding
metal Teodolinda,waspartially sheltered
installed for thefrom
entirethe rain. Aof
duration seventeen-floor metal scaffolding
the pilot site activity, was
allowing for installed
stable and
for the entire duration of the pilot site activity, allowing for stable and close-range access
close-range access to all the stone surfaces for the diagnostic, testing, and monitoring operations to all the
stone surfaces
(Figure 1b). for the diagnostic, testing, and monitoring operations (Figure 1b).

Figure 1.
Figure (a) Orthophoto
1. (a) Orthophoto documentation
documentationof
ofthe
the façade
façade of
of the
the Monza
Monza cathedral;
cathedral; (b)
(b) detail
detail of
of the
the pilot
pilot
site area
site area with
with scaffolding.
scaffolding.

3. General Framework of the Pilot Conservation Site

3. General Framework of the Pilot Conservation Site
The pilot site approach is a process of increasing knowledge, which progressively integrates the
The pilot site approach is a process of increasing knowledge, which progressively integrates the
results from multidisciplinary research contributions to support the definition of the conservation
results from multidisciplinary research contributions to support the definition of the conservation
project. The pilot site activity can be divided into three main phases—the condition survey and
project. The pilot site activity can be divided into three main phases—the condition survey and
material characterization, the assessment of the conservation treatments, and the scale-up for the
material characterization, the assessment of the conservation treatments, and the scale-up for the
executive project. The core activities of the pilot site are mainly concentrated within the first two
executive project. The core activities of the pilot site are mainly concentrated within the first two
phases, while the final one represents the actual link to the design and management of the global
phases, while the final one represents the actual link to the design and management of the global
intervention. The phases, objectives, and results of the pilot site are summarized in Figure 2.
intervention. The phases, objectives, and results of the pilot site are summarized in Figure 2.
During the first phase, all the relevant information for a thorough understanding of the site
During the first phase, all the relevant information for a thorough understanding of the site in
in its own integrity and complexity are gathered and elaborated. These include the historical data
its own integrity and complexity are gathered and elaborated. These include the historical data of the
of the construction activities and the interventions carried out during the centuries, as well as the
construction activities and the interventions carried out during the centuries, as well as the spatial
spatial and geometrical features of the site. The preliminary knowledge is then completed with the
and geometrical features of the site. The preliminary knowledge is then completed with the
information regarding the materials, the assessment of their state of conservation according to the
information regarding the materials, the assessment of their state of conservation according to the
current guidelines and standard for cultural heritage preservation [33–35], and the identification of the
current guidelines and standard for cultural heritage preservation [33–35], and the identification of
deterioration mechanisms.
the deterioration mechanisms.
In the second phase, all the operative actions to ensure the best possible preservation of the
In the second phase, all the operative actions to ensure the best possible preservation of the
materials are set up and implemented. By exploiting the extensive supporting information resulting
materials are set up and implemented. By exploiting the extensive supporting information resulting
from phase one, the conservative issues and local critical situations are evidenced. The knowledge
from phase one, the conservative issues and local critical situations are evidenced. The knowledge of
of the site geometrical features, materials, and precise state of conservation supports the selection
the site geometrical features, materials, and precise state of conservation supports the selection of the
of the most appropriate areas (as for orientation, type of substrate, and main deterioration patterns)
most appropriate areas (as for orientation, type of substrate, and main deterioration patterns) to test
to test specific conservation procedures (i.e., cleaning, consolidation, and/or surface protection).
specific conservation procedures (i.e., cleaning, consolidation, and/or surface protection). Monitoring
Monitoring the medium-term results of the treatments (generally around a 12-month period) is an
the medium-term results of the treatments (generally around a 12-month period) is an additional and
additional and highly desirable outcome of this phase. It can provide extremely valuable indications
highly desirable outcome of this phase. It can provide extremely valuable indications about the
durability and compatibility of the tested solutions, to be added to the laboratory artificial aging tests.
The last phase is the scale-up of all the operations (the type of materials, different operative
parameters, and timing) to define the technical details for the conservation project. As might be
Heritage 2019, 2 FOR PEER REVIEW 5

Heritage 2019, 2 801

expected, adjustments, integrations, and re-thinking of some solutions are necessary during this
phase to solve all the additional issues resulting from the change of scale and the related increased
complexity. The pilotand
about the durability site compatibility
approach alsooflimits the risk
the tested of over-simplified
solutions, to be addedinterpretation of the
to the laboratory actual
artificial
conditions
aging tests.and allows for increasing the flexibility and sustainability of the defined solutions.

Figure
Figure2.2.Scheme
Schemeof
ofthe
thepilot
pilotconservation
conservationsite
sitephases,
phases,objectives,
objectives,and
and results.
results.

The1:last
4. Phase phase isSurvey
Condition the scale-up of all the operations
and Characterization (the type of materials, different operative
of Materials
parameters, and timing) to define the technical details for the conservation project. As might be
Gathering all the historical data from different sources (such as archives, cultural heritage
expected, adjustments, integrations, and re-thinking of some solutions are necessary during this phase
databases, records of previous work retrieved from the professionals involved, etc.) is a necessary
to solve all the additional issues resulting from the change of scale and the related increased complexity.
and fundamental step to identify the construction/modification phases, as well as the restoration and
The pilot site approach also limits the risk of over-simplified interpretation of the actual conditions
maintenance activities, that occurred over time [36,37]. All these operations are part of the inherent
and allows for increasing the flexibility and sustainability of the defined solutions.
stratification process of the site, eventually leading to its current configuration, and must be properly
recognized
4. Phase 1: as they contribute
Condition Surveyto theCharacterization
and overall historic value. The geometric survey is the operative tool
of Materials
to translate the historical data and the onsite observations into thematic maps, to achieve a thorough
Gathering
knowledge allmaterials
of the the historical data state
and their fromofdifferent sources
conservation. (suchmaps
These as archives,
constitutecultural
the basis heritage
for a
databases, records of previous
coherent conservation project [38]. work retrieved from the professionals involved, etc.) is a necessary
and Considering
fundamental the stepremarkable
to identify size
the construction/modification
of the façade (30 m at the base, phases,
withasawell as the restoration
maximum height around and
maintenance activities, that occurred over time [36,37]. All these operations
40 m) and the complexity of the architectural and decorative elements, the geometric survey was are part of the inherent
stratification
based process of the site,
on a photogrammetric eventually
approach. leading
Figure to its current
1a shows configuration,
the orthophoto of theand mustfrom
façade, be properly
which
recognized
two as theyreference
cartographic contribute to the
maps withoverall historic
drawing value.
scales Theand
of 1:50 geometric
1:20 forsurvey is thedetailed
the highly operative tool
areas
to translate the historical data and the onsite observations into thematic maps,
were derived. The current technical standard [34] and international guidelines [35,39] provide the to achieve a thorough
knowledge
glossary for of
thethe materials and
identification of their state of conservation.
the constituent materials and These maps constitute
deterioration patterns theafter
basisvisual
for a
coherent conservation project [38].
examination of architectural elements and surfaces. The location of the different materials in the pilot
Considering
site was annotated, theand
remarkable
the precisesize of the façadeof(30
identification themlithotypes
at the base,was
with
inasome
maximum
cases height around
confirmed by
40 m) and the investigations
petrographical complexity of of the architectural
stone and evaluation
samples. This decorative waselements, the geometric
then extended from the survey
pilot was
site
based
to the on a photogrammetric
scale of the entire façade, approach.
assumingFigure 1a shows scheme
a recurrent the orthophoto of the façade,
of application from which
of lithotypes and
two cartographic reference maps with drawing scales of 1:50 and 1:20 for the
exploiting the detailed photographic documentation acquired with the photogrammetric survey. The highly detailed areas
wereresult
final derived. Theactivity
of this currentwastechnical standard
a thematic map of [34]theand international
façade guidelines
in the drawing [35,39]
scale 1:50 provide
(Figure the
3, left)
glossary for the identification of the
showing materials identification and location. constituent materials and deterioration patterns after visual
examination of architectural elements and surfaces. The location of the different materials in the pilot
site was annotated, and the precise identification of the lithotypes was in some cases confirmed by
petrographical investigations of stone samples. This evaluation was then extended from the pilot site to
the scale of the entire façade, assuming a recurrent scheme of application of lithotypes and exploiting
the detailed photographic documentation acquired with the photogrammetric survey. The final result
of this activity was a thematic map of the façade in the drawing scale 1:50 (Figure 3, left) showing
materials identification and location.
Heritage 2019, 2 802
Heritage 2019, 2 FOR PEER REVIEW 6

Figure 3. (Left) materials mapping; (right) deterioration patterns mapping.

Figure 3. (Left) materials mapping; (right) deterioration patterns mapping.
Heritage 2019, 2 803
Heritage 2019, 2 FOR PEER REVIEW 7

This
This map
map confirmed
confirmed thethe extensive presence of
extensive presence of Oira
Oira stone
stone forfor the
the dark
dark alternated
alternated rows
rows ofof the
the
cladding, whereas the white ones are currently made mainly of Crevola stone,
cladding, whereas the white ones are currently made mainly of Crevola stone, a dolomitic marble. In a dolomitic marble.
In some
some areas,
areas, however,
however, thisstone
this stonewaswassubstituted
substitutedeither
eitherby byMusso
Musso or or by
by Candoglia,
Candoglia, calcitic
calcitic and
and
medium-to-coarse
medium-to-coarse grained marbles. Candoglia marble is also the main stone employed for the
grained marbles. Candoglia marble is also the main stone employed for the
crowning
crowning elements
elementsandandspires
spiresthat belong
that to ato
belong single and latest
a single construction
and latest phase.phase.
construction The greatest variety
The greatest
of lithotypes
variety were observed
of lithotypes in the frames
were observed in theand decorations
frames of the double-
and decorations of theand triple-arched
double- windows,
and triple-arched
to create a remarkable decorative pattern by alternating Rosso di Verona (a
windows, to create a remarkable decorative pattern by alternating Rosso di Verona (a red-coloredred-colored limestone),
white Apuanwhite
limestone), marble, Molera
Apuan stoneMolera
marble, (a gray stone
sandstone),
(a grayand Oira stoneand
sandstone), (Figure
Oira4a).
stoneThe(Figure
finely sculpted
4a). The
internal decorations
finely sculpted were
internal realized by
decorations Viggiù
were stone
realized by(a brownstone
Viggiù to gray calcitic
(a brown tolimestone)
gray calcitic and Angera
limestone)
stone
and Angera stone (dolostone). The double-arched windows also showed a rather articulatedsimilar
(dolostone). The double-arched windows also showed a rather articulated usage of usage
stones,
of similarwith Apuan
stones, withmarble
Apuaninmarble
the frames,
in theAngera
frames, stone
Angerainstone
the lateral
in thefriezes, Aurisina
lateral friezes, stone in
Aurisina the
stone
capital
in the capital of the central column, and Serizzo, a very durable metamorphic grey stone, in sill.
of the central column, and Serizzo, a very durable metamorphic grey stone, in the window the
The
windowsmallsill.
rose-window and its surrounding
The small rose-window decoration were
and its surrounding realizedwere
decoration alternating
realizedwhite elements
alternating of
white
Candoglia
elements ofand Musso marbles
Candoglia and Musso mounted
marblesonmounted
top of Oiraonstone
top ofslabs
Oira(Figure 4b). (Figure 4b).
stone slabs

Figure 4.4.(a)
(a)The
The articulate
articulate decorative
decorative usage
usage of various
of various stones
stones in in the triple-arch
the triple-arch window;
window; (b) (b)
decorative
decorative
tiles tilesand
in Musso in Musso and marble
Candoglia Candoglia
andmarble and Oira stone.
Oira stone.

The main deterioration phenomena affecting the different elements and lithotypes were
carefully observed and identified throughout the pilot site, according to the current Italian standard
definition [34]. The use of portable diagnostic techniques, techniques, suchsuch as digital
digital microscopy, allowed for a
better understanding of the weathering effects on the different stones and supported the successive
laboratory diagnostic
diagnostic phase,
phase,minimizing
minimizingthe thenumber
numberofof collected
collected samples
samples andand analyses.
analyses. Finally,
Finally, the
the observations
observations carried
carried out on outtheonpilot
the pilot site, together
site, together with the with the highly
highly detaileddetailed
imagesimages
acquired acquired
during
during thesurvey,
the initial initial survey,
allowedallowed
for drawingfor drawing
a completea complete state of conservation
state of conservation of the
of the façade façade
with with
sufficient
sufficient
accuracy. accuracy.
The complexity of the conservative
conservative conditions, due to the overlappingoverlapping of several
several deterioration
deterioration
patterns onto specific elements or limited areas (Figure 5), required a suitable suitable interpretation of the
data to produce a synthetic and effective output. The The final
final graphic
graphic representation,
representation, therefore, grouped
together those deterioration forms, showing a clear relationship with specific lithotypes in separated
maps. In In this
this way,
way, four
four final thematic
thematic maps of the deterioration patterns provided an effective
description of the overall surface
surface deterioration.
deterioration.
In Figure 3, right, is reported
Figure 3, right, is reported ananexample
example of the resulting
of the deterioration
resulting map.map.
deterioration Concerning
Concerningthe state
the
of conservation
state of Crevola
of conservation stone, the
of Crevola mapthe
stone, shows
mapthe remarkable
shows concentration
the remarkable of chromatic
concentration alteration
of chromatic
phenomena on the surfaces
alteration phenomena on theofsurfaces
the slabs. Thisslabs.
of the pattern
Thisispattern
clearly isassociated with the loss
clearly associated withofthematerial
loss of
(confirmed by the surface irregular geometry also observable in the map),
material (confirmed by the surface irregular geometry also observable in the map), due to thedue to the extensive erosion
clearly visible
extensive along
erosion the edges.
clearly visibleErosion
along isthealso particularly
edges. Erosionintense
is alsoin the Crevolaintense
particularly columnsin in
thethe upper
Crevola
part of theinfaçade,
columns which
the upper areofheavily
part subjected
the façade, which to are
the heavily
direct rainfall, withtoboth
subjected the mechanical andwith
direct rainfall, chemical
both
action. Evidently, the map shows that the crowning element of the façade and
mechanical and chemical action. Evidently, the map shows that the crowning element of the façade the spires, mostly made
of
andCandoglia
the spires,marble,
mostlyaremade
criticalofareas with respect
Candoglia marble,to these same deterioration
are critical patterns.
areas with respect to these same
deterioration patterns.
Heritage 2019, 2 804
Heritage 2019, 2 FOR PEER REVIEW 8

Figure 5.
Figure 5. Conservative
Conservative conditions
conditions of of the
the stone
stone elements
elements of
of the
the façade:
façade: (a)
(a) Granular
Granular disintegration
disintegration and
and
microcracks on
microcracks on aa Musso
Musso tiles;
tiles; (b)
(b) chromatic
chromatic alteration
alteration and
and extensive
extensive erosion
erosion of
of aa Crevola
Crevola ashlar;
ashlar; (c)
(c)
oxalate patina and soiling on a Musso decorative element; (d) biological colonization of
oxalate patina and soiling on a Musso decorative element; (d) biological colonization of the crowning the crowning
elements;(e)
elements; (e)chromatic
chromaticalteration
alterationandand biological
biological colonization
colonizationonon Candoglia
Candogliamarble;
marble;(f)
(f) extensive
extensive black
black
crust formation,
crust formation, microcracks,
microcracks,andandgranular
granulardisintegration
disintegrationofofaamarble
marblecapital.
capital.

The
Theprecise
preciseidentification
identification of the
of main
the maindamage mechanisms
damage was achieved
mechanisms by meansby
was achieved of ameans
traditional
of a
multi-analytical diagnostic approach in the lab. This included optical and
traditional multi-analytical diagnostic approach in the lab. This included optical and scanningscanning electron microscopy,
Fourier-transformed
electron microscopy, infrared spectroscopy,infrared
Fourier-transformed and X-ray diffraction and
spectroscopy, analysis. Specific diagnostic
X-ray diffraction analysis.
techniques were also
Specific diagnostic employed
techniques to also
were analyze the extensive
employed to analyze biocolonization affecting the crowning
the extensive biocolonization affecting
element of theelement
the crowning façade, to of better understand
the façade, to better theunderstand
potential damaging
the potentialroledamaging
of the biofilms [40].
role of theThis last
biofilms
phase of the
[40]. This preliminary
last phase of the knowledge
preliminaryof the site features
knowledge of highlighted, as expected,
the site features highlighted,that the depositionthat
as expected, of
particulate
the depositionmatter and black matter
of particulate crust formation
and blackwere crustmajor damage
formation weremechanisms
major damage of the stone elements
mechanisms of the
partially shelteredpartially
stone elements from thesheltered
rain runoff. In particular,
from intense In
the rain runoff. deposition withintense
particular, a sulfate- and nitrate-rich
deposition with a
composition
sulfate- and was detectedcomposition
nitrate-rich all over the stone frames surrounding
was detected all over thethestone windows,
frameswhereas thick and
surrounding the
partially fractured black crust covered the windows capitals as well as several
windows, whereas thick and partially fractured black crust covered the windows capitals as well as areas of the marble
decorative
several areas elements. The results
of the marble of the diagnostics
decorative elements. The conducted
results on the elements
of the diagnostics subjected
conducted to erosion
on the
allowed
elementsfor assessing
subjected tothe magnitude
erosion allowed of for
theassessing
loss of mechanical cohesion
the magnitude of the
of the lossstone surfaces. All
of mechanical these
cohesion
data were crucial to define an updated scenario of the type and level of risks
of the stone surfaces. All these data were crucial to define an updated scenario of the type and level affecting the different
areas and,
of risks therefore,
affecting the to select the
different most
areas and,suitable operative
therefore, conservation
to select actions operative
the most suitable for the specific issues.
conservation
Thefor
actions slabs
the of the cladding
specific issues. actually represented a particularly critical situation, because of their
remarkable
The slabsextension on the façade
of the cladding actuallyandrepresented
being realized with two stone
a particularly criticaltypes with because
situation, rather different
of their
characteristics and durability.
remarkable extension A comparative
on the façade and being evaluation
realized withof thetwo
state of conservation
stone of Crevola
types with rather and
different
Oira stone by means of selected diagnostic results is reported in Figure 6. An
characteristics and durability. A comparative evaluation of the state of conservation of Crevola and intense color alteration
affects bothby
Oira stone stones
means and represents
of selected a primary
diagnostic conservation
results is reported issue as it has
in Figure significantly
6. An intense colorchanged the
alteration
aesthetic appearance
affects both stones and of represents
the whole façade.
a primary Theconservation
diagnostic investigation
issue as it hasshed light on this
significantly peculiar
changed the
alteration, which is determined by rather different deterioration phenomena,
aesthetic appearance of the whole façade. The diagnostic investigation shed light on this peculiar depending on the
different
alteration,mineralogical nature of the
which is determined by two stones.
rather different deterioration phenomena, depending on the
different mineralogical nature of the two stones.
The Crevola slabs show intense darkening of the exposed surfaces. Such an effect irregularly
affects the stone due to the concurrent loss of material from the outermost portion (Figure 6a), which
is determined by the formation of a diffused network of microcracks crossing the single dolomite
grains (Figure 6b). The resulting fissures are progressively filled by atmospheric deposits, which
contribute to the macroscopic darkening effect observed (Figure 6c). The surface mechanical
resistance of the stone is further compromised by the loss of cohesion of the matrix, showing clear
and extensive detachments along the grain borders. The dolomitic nature of Crevola marble is
conservation of the crystalline matrix of the stone. This is related to the specific geological,
petrographic, and compositional features of this silicate-rich serpentinite. Its color alteration results
from the selective chemical leaching of the magnesium ions from the phyllosilicate structure,
followed by surface recrystallization of low-ordered silicon oxides, due to the interaction with rain
and moisture
Heritage 2019, 2 [41]. This process did not significantly affect the mechanical cohesion of the stone,805
except for the formation of thin scales which eventually detached from the surface (Figure 6f).

Figure 6.
Figure 6. (a)
(a) Conservative
Conservative conditions
conditions ofof the
the Crevola
Crevola cladding;
cladding; (b)
(b) extensive surface decohesion
extensive surface decohesion of
of the
the
stone matrix
stone matrix and fissuring of
and fissuring of the
the grains
grains of
of Crevola under SEM
Crevola under SEM observation;
observation; (c)
(c) polished
polished cross-section
cross-section
showing the
showing the accumulation
accumulation of environmental pollutants
of environmental pollutants (arrow);
(arrow); (d)
(d) photographic
photographic documentation
documentation ofof
Oira stone
stonecladding;
cladding;(e)(e) SEM observation of the surface condition with limited microcracks;
SEM observation of the surface condition with limited microcracks; (f) polished (f)
polished cross-section
cross-section showing
showing the the detachment
detachment of scale
of a surface a surface scale (arrow).
(arrow).

The 2:
5. Phase Crevola slabs show
Assessment of Theintense darkening
Conservation of the exposed surfaces. Such an effect irregularly
Treatments
affects the stone due to the concurrent loss of material from the outermost portion (Figure 6a), which is
During this phase, suitable portions of the surface, representative of the most relevant
determined by the formation of a diffused network of microcracks crossing the single dolomite grains
conservation conditions, are selected as playground areas for testing. Each playground is then
(Figure 6b). The resulting fissures are progressively filled by atmospheric deposits, which contribute to
subdivided into trail areas where different treatment procedures can be performed and compared.
the macroscopic darkening effect observed (Figure 6c). The surface mechanical resistance of the stone
The contribution of the restorer is particularly important with respect to the proposal of the materials
is further compromised by the loss of cohesion of the matrix, showing clear and extensive detachments
and conservation methodologies to be tested, the identification of the playgrounds (which should
along the grain borders. The dolomitic nature of Crevola marble is particularly sensitive to the action
also meet requirements of accessibility of operators and instrumentations), the preparation of the
of the rain runoff, causing mechanical and chemical erosion, and also by the cyclic environmental
surfaces in view of the conservative treatments, and the appropriate setup of the application methods
thermal stresses, which can amplify the magnitude of the loss of cohesion between the grains. This is
and related parameters.
confirmed by the characteristic intensity and distribution of the damage—the deterioration mapping
According to the extremely compromised state of conservation of the carbonatic stones of the
clearly showed an increasing magnitude from the top elements down to the base of the façade, where
cladding and the sculpted elements of the windows, the activity on the façade was focused on testing
the cumulative effects of the direct rain and the rain runoff are particularly intense.
the cleaning, consolidation, and protection procedures on these materials. A specific playground was
The color alteration of the Oira stone consists of the fading of the original dark green hue towards
also identified to face the extensive biocolonization of the crowning elements and spires.
a pale grey-to-blue one, which is associated with a scaling along the slab borders and cracks (Figure 6d).
The SEM observation of Oira surfaces (Figure 6e) confirmed the overall good state of conservation of the
crystalline matrix of the stone. This is related to the specific geological, petrographic, and compositional
features of this silicate-rich serpentinite. Its color alteration results from the selective chemical leaching
of the magnesium ions from the phyllosilicate structure, followed by surface recrystallization of
low-ordered silicon oxides, due to the interaction with rain and moisture [41]. This process did not
significantly affect the mechanical cohesion of the stone, except for the formation of thin scales which
eventually detached from the surface (Figure 6f).

5. Phase 2: Assessment of The Conservation Treatments

During this phase, suitable portions of the surface, representative of the most relevant conservation
conditions, are selected as playground areas for testing. Each playground is then subdivided into
trail areas where different treatment procedures can be performed and compared. The contribution of
the restorer is particularly important with respect to the proposal of the materials and conservation
Heritage 2019, 2 806

methodologies to be tested, the identification of the playgrounds (which should also meet requirements
of accessibility of operators and instrumentations), the preparation of the surfaces in view of the
conservative treatments, and the appropriate setup of the application methods and related parameters.
According to the extremely compromised state of conservation of the carbonatic stones of the
cladding and
Heritage 2019, thePEER
2 FOR sculpted
REVIEW elements of the windows, the activity on the façade was focused on testing 10
the cleaning, consolidation, and protection procedures on these materials. A specific playground was
also identified to face the
The playgrounds for extensive
the cleaning biocolonization
included Crevola of the crowning
stone elements
cladding, Angera and spires.
stone and Candoglia
marbleThe playgrounds
capitals, Mussofor the cleaning
marble included
and Viggiù stoneCrevola
elements,stone
andcladding,
Rosso diAngera
Veronastone and Candoglia
and Carrara marble
marble of
frames capitals, Musso marble
the windows. and Viggiù stone
The consolidation elements,
and surface and Rosso
protection di Verona were
playgrounds and Carrara
mainly
marble framesonofCrevola
concentrated the windows.
stone, The consolidation
Candoglia and Mussoand surface
marble.protection playgrounds
Eight different cleaningwere mainly
procedures
concentrated
were on Crevola
tested, including stone, Candoglia
water-based methods, and Musso marble.
controlled Eight different
micro-sandblasting, cleaning
chemical procedures
poultices, and
were cleaning.
laser tested, including water-based methods, controlled micro-sandblasting, chemical poultices, and
laserThe
cleaning.
pilot site approach successfully targeted the cleaning of the colored stones and the surfaces
with The pilotpatina
residual site approach successfully
and finishing. This was targeted thefor
the case, cleaning
example,of the
for colored stones
the capitals andtriple-arched
of the the surfaces
with residual
window of thepatina
lowerand finishing.
level This was
of the façade the case,
(Figure for example,
7). Their for the capitals
state of conservation wasof characterized
the triple-arched by
awindow
thick andof the lower level
adherent blackof the façade
crust, with an (Figure 7). Their
eminently statecomposition
sulfatic of conservation thatwas characterized
completely by a
concealed
thick
the and adherent
marble substrate. black crust, with
Moreover, the an eminentlycharacterization
preliminary sulfatic composition that completely
highlighted the presenceconcealed the
of a red-
marble substrate.
colored oxalate-rich Moreover,
patina atthethepreliminary characterization
interface between the stone highlighted
and the crust. theSuch
presence
patina ofwas
a red-colored
therefore
oxalate-richaspatina
identified at thelayer
the target interface
for between the stone
the evaluation of and
the the crust. efficacy
cleaning Such patina andwas thereforeBoth
selectivity. identified
laser
as the target
cleaning andlayer for themicro-sandblasting
controlled evaluation of the cleaning
were ableefficacy and selectivity.
to effectively removeBoth the laser cleaning
sulfatic crust and
controlledthe
preserve micro-sandblasting were able
target layer. Actually, to effectively remove
micro-sandblasting the sulfatic
employing roundedcrustand
andsoft
preserve the target
inert and laser
layer. Actually,
cleaning micro-sandblasting
with tunable fluency are highlyemploying rounded
controllable and soft inertfor
methodologies andthelaser cleaning
selective with tunable
removal of very
fluency
thin are highly
surface layers,controllable
as they allow methodologies for the selective
a constant evaluation removal results
of the cleaning of very during
thin surface layers, as
the treatment.
they allowgiven
Moreover, a constant evaluation
the limited of theofcleaning
extension results
the surfaces to beduring theboth
treated, treatment.
cleaning Moreover,
techniques given the
proved
limited
to extension ofbeing
be sustainable, the surfaces
time- andto becost-effective.
treated, both cleaning techniques of
The contribution proved to be sustainable,
the diagnostic allowed being
for
time- andthe
defining cost-effective.
best operative The condition
contribution forofthethelaser
diagnostic
cleaningallowed for defining
and selecting the best operative
appropriate working
pressures
condition for mechanical cleaning.
the laser cleaning and selecting appropriate working pressures for mechanical cleaning.

Figure 7.
Figure (a)Trial
7. (a) Trial area
area for
for the
the cleaning
cleaning of
of the
the capitals
capitals before
before (left
(left side
side ofof the
the element)
element) and
and after
after cleaning
cleaning
(right side); (b) polished cross-section showing the marble substrate (1) covered by the
(right side); (b) polished cross-section showing the marble substrate (1) covered by the red oxalate- red oxalate-rich
patina
rich (2, target
patina layerlayer
(2, target of theofcleaning) and the
the cleaning) andsulfatic crust crust
the sulfatic (3); (c)(3);
microphotograph of the of
(c) microphotograph result of the
the result
treatment after laser cleaning and (d) after controlled micro-sandblasting.
of the treatment after laser cleaning and (d) after controlled micro-sandblasting.

As far as the Crevola slabs of the cladding are concerned, the particularly poor conservation
As far as the Crevola slabs of the cladding are concerned, the particularly poor conservation
conditions of the surfaces that emerged after phase 1 of the pilot site activity suggested the adoption of
conditions of the surfaces that emerged after phase 1 of the pilot site activity suggested the adoption
a mild cleaning technique and the testing of suitable treatments to stabilize and protect the crystalline
of a mild cleaning technique and the testing of suitable treatments to stabilize and protect the
matrix. Three playgrounds were identified for cleaning, consolidation, and surface protection, between
crystalline matrix. Three playgrounds were identified for cleaning, consolidation, and surface
the ground level and around 16 m height.
protection, between the ground level and around 16 m height.
Ten different trial areas with similar surface conditions were defined to test and compare cleaning
Ten different trial areas with similar surface conditions were defined to test and compare
procedure, based on nebulized water, different types of micro-sandblasting, and chemical poultices.
cleaning procedure, based on nebulized water, different types of micro-sandblasting, and chemical
poultices. The evaluation criteria [42] were the efficiency of the cleaning in the removal of deposits,
possibility to tune the cleaning action according to different levels of surface cohesion, minimization
of the loss of materials from the stone matrix, sustainability in terms of cost, and duration of the
operation. This last aspect, in particular, was a relevant issue considering the extent of the surfaces to
be treated. The multi-analytical diagnostic evaluation of the playgrounds and the feedback from the
Heritage 2019, 2 807

The evaluation criteria [42] were the efficiency of the cleaning in the removal of deposits, possibility
to tune the cleaning action according to different levels of surface cohesion, minimization of the loss
of materials from the stone matrix, sustainability in terms of cost, and duration of the operation.
This last aspect, in particular, was a relevant issue considering the extent of the surfaces to be treated.
The multi-analytical diagnostic evaluation of the playgrounds and the feedback from the restorer who
conducted the pilot treatments pointed out that the micro-sandblasting was a suitable methodology to
reach
Heritageacceptable cleaning results (Figure 8). Further investigations were then conducted to optimize
Heritage 2019,
2019, 22 FOR
FOR PEER
PEER REVIEW
REVIEW 11
11
the working parameters, in particular, the working pressure, the distance from the surface, and the
type of aggregate.
the surface, Controlled
and the type of and low-pressure
aggregate. cleaning
Controlled andusing rounded dolomitic
low-pressure aggregate
cleaning using was
rounded
finally implemented.
dolomitic aggregate was finally implemented.

Figure 8.
Figure 8.
Figure Selected
8. Selected results
Selected results from
results from the
from the playground
the playground
playground for for the
for the setup
the setup
setup ofof the
of the cleaning
the cleaning
cleaning ofof Crevola
of Crevola after
Crevola after digital
after digital
digital
onsite microscopy
onsite microscopy
onsite microscopy and and SEM
and SEM (left
SEM (left to
(left to right
to right respectively).
right respectively). (a)
respectively). (a) Surface
(a) Surface before
Surface before cleaning;
before cleaning; (b)
cleaning; (b) surface
(b) surface after
surface after
after
cleaning with
cleaning with
cleaning the
with the implemented
the implemented methodology
implemented methodology showing the
methodology showing the removal
removal
removal of of the
of the surface
the surface deposits
surface deposits
deposits andand the
and the
the
preservation
preservationof
preservation of the
ofthe outermost
theoutermost stone
outermoststone grains.
stonegrains.
grains.

The setup
The setup ofof the
the consolidation
consolidation and and surface
surface protection
protection treatments
treatments followed
followed the definition of
the definition of the
the
cleaning procedure.
cleaning procedure. The The response
response andand efficacy of such treatments
treatments indeed
indeed depend
depend on on the surface
the surface
conditions, which
conditions, are significantly modified upon cleaning (and according
which are significantly modified upon cleaning (and according to the different to the different cleaning
cleaning
methodologies). The
methodologies). The pilot
pilot application
application of of the
the treatments
treatments was was then
then carried
carried out
out on
on 15
15 trial
trial areas.
areas.
The testing
The testing of
of the treatments was
the treatments was carried
carried outout in
in different
different steps
steps (Figure
(Figure 9).
9). The
The first activities were
first activities were
focused on
focused on the
the selection
selection ofof the
the materials
materials and
and the
the tuning
tuning of the
of the application
application parameters.
parameters. After
After a suitable
a suitable
curing period
curing period upon
upon application,
application, thethe control activities based
control activities based on standard protocols
on standard protocols and
and onsite
onsite testing
testing
methodologies were
methodologies were conducted
conducted to to assess
assess and
and monitor
monitor thethe products
products performances
performances [13,17].
[13,17]. During
During the the
setup phase
setup phase (Figure
(Figure 9),
9), two
two commercial
commercial tetraethyl-orthosilicate
tetraethyl-orthosilicate (TEOS) were
(TEOS) were identified
identified and
and tested
tested
alone and
alone and inin association
association with
with anan ammonium
ammonium oxalateoxalate treatment.
treatment. The objective
objective was
was to evaluate the
to evaluate the
possible contribution
possible contribution provided
provided by by the
the formation
formation of of aa stable
stable surface layer of calcium oxalate
surface layer of calcium oxalate [43] [43] from
from
the combined
the combined approach,
approach, in in comparison
comparison withwith the
the efficacy
efficacyof ofTEOS
TEOSalone.
alone.

Figure
Figure 9. Flow chart summarizing the operative steps for the definition of the consolidation and surface
Figure 9.
9. Flow
Flow chart
chart summarizing
summarizing the
the operative
operative steps
steps for
for the
the definition
definition of
of the
the consolidation
consolidation and
and
protection
surface methodologies.
surface protection
protection methodologies.
methodologies.

A similar approach was used for the setup of the protective systems, which included commercial
stone coatings (organosiloxanes, alkylalkoxy-silane, and functionalized SiO22 products) and
innovative treatments based on TiO22 nanoparticles [17].
After proper curing time defined according to the specific requirements of the different
products, the efficacy of the treatments was investigated by onsite testing of the surface stability and
the mechanical cohesion for the consolidants, and the water absorption capability for the protective
systems. In particular, a combined investigation of the very superficial stone layers and the more in-
Heritage 2019, 2 808

A similar approach was used for the setup of the protective systems, which included commercial
stone coatings (organosiloxanes, alkylalkoxy-silane, and functionalized SiO2 products) and innovative
treatments based on TiO2 nanoparticles [17].
After proper curing time defined according to the specific requirements of the different products,
the efficacy of the treatments was investigated by onsite testing of the surface stability and the
mechanical cohesion for the consolidants, and the water absorption capability for the protective
systems. In particular, a combined investigation of the very superficial stone layers and the more
in-depth consolidation effects was achieved by means of peeling tests and micro-drilling (DRMS,
Drilling
Heritage Resistance
2019, Measurement
2 FOR PEER REVIEW System) measurements (Figure 10). 12

Figure 10. Phases

Figure 10. Phasesofofthethe pilot
pilot conservation
conservation activity
activity for thefor theofsetup
setup of consolidation
consolidation and
and surface surface
protection:
protection: (a) application;
(a) treatment’s treatment’s application; (b)
(b) evaluation ofevaluation of the
the treatment’s treatment’s
results results
by means by means
of digital of digital
microscopy and
microscopy and (c) VIS-spectrophotometric
(c) VIS-spectrophotometric measurements; (d)measurements;
evaluation of the (d)water
evaluation of thebehavior
absorption water absorption
and, (e) of
behavior and, (e)
the mechanical of the mechanical
cohesion by means ofcohesion by means of DRMS measurements.
DRMS measurements.

Moreover, as the
Moreover, the aesthetic
aesthetic compatibility
compatibility of of such
such treatments
treatments is is aa relevant
relevant requirement
requirement in in cultural
cultural
heritage, the testing protocol
heritage, the testing protocol also included the assessment of the surface color change.
The overall
The overall sustainability
sustainability ofof the
the consolidation
consolidation and,
and, in
in particular,
particular, thethe protective
protective treatments,
treatments, hashas
to be
to be carefully
carefully balanced
balanced according
according to to their
their durability
durability in
in the
the actual
actual exposure
exposure conditions.
conditions. This
This is
is also
also
an issue
an issue that
that can
can be
be more
more effectively
effectively tackled
tackled when
when aa pilot
pilot conservation
conservation site site approach
approach supports
supports thethe
traditional laboratory
traditional laboratory investigation.
investigation. In Inthe
thecase
casestudy,
study, the
the monitoring
monitoring period
period of
of protective
protective treatments
treatments
was limited
was limited to
to 12
12 months,
months, but
but the
the final
final evaluation
evaluation and
and selection
selection were
were based
based also
also on
on the
the results
results of
of the
the
accelerated aging
accelerated aging test
test in
in the
the lab.
lab.

6. Phase
6. Phase 3:
3: Scale-Up
Scale-Up for
forthe
the Executive
Executive Project
Project
The complete
The complete corpus
corpus of of information
information resulting
resulting fromfrom the
the pilot
pilot site
site activity
activity waswas the
the working
working basebase
to scale
to scale up
up the
the procedures
procedures to to be
be adopted
adopted in in the
the executive
executive conservation
conservationprojectprojectof ofthe
theentire
entirefaçade.
façade.
The main objectives of this last phase included the precise definition of the
The main objectives of this last phase included the precise definition of the final conservation final conservation activities,
their scheduling,
activities, and the cost
their scheduling, andassessment and check of
the cost assessment thecheck
and overallof sustainability of the intervention.
the overall sustainability of the
The operative tools implemented in this phase were the mapping of the
intervention. The operative tools implemented in this phase were the mapping of the interventionsinterventions and the related
technical
and working
the related sheets.working sheets.
technical
The mapping
The mapping of of the
the interventions
interventions was was based
based onon the
the geometric
geometric survey
survey andand reported
reported thethe precise
precise
locations and extent of the different conservation activity planned for all the
locations and extent of the different conservation activity planned for all the areas of the façade. In areas of the façade. In
such a way, and with the support of the information gathered from the
such a way, and with the support of the information gathered from the deterioration patterns deterioration patterns mapping
and the results
mapping and theof results
the pilot ofsite, a series
the pilot site,ofaoperations were prescribed
series of operations to target each
were prescribed specific
to target eachconditions
specific
conditions in terms of the type of substrate and state of conservation. The mapping of also
in terms of the type of substrate and state of conservation. The mapping of the interventions the
provided an estimation
interventions also provided of theansurface areas toofbethe
estimation subjected
surfacetoareas
the different sequencestoofthe
to be subjected conservative
different
treatments,ofwhich
sequences were automatically
conservative treatments, calculated
which were by automatically
CAD software.calculated
This evaluation
by CAD was fundamental
software. This
for the management of the different phases of the intervention
evaluation was fundamental for the management of the different phases of the interventionand the assessment of theand
overall
the
sustainability
assessment of of
thethe process.
overall On the basis
sustainability ofofthethis information,
process. On thethe economic
basis assessment was
of this information, theperformed,
economic
and a cost-effectiveness
assessment was performed, evaluation
and awas carried out to define
cost-effectiveness the allocation
evaluation of the resources.
was carried out to define the
The mapping of
allocation of the resources. the intervention was integrated by technical working sheets, which described
the operative
The mapping procedures implementedwas
of the intervention during phase 2.
integrated byThe technical
technical working
working sheets
sheets, weredescribed
which designed
to provide practical guidelines for the operators working onsite through
the operative procedures implemented during phase 2. The technical working sheets were designed step-by-step protocols.
They
to contained
provide highly-detailed
practical guidelines forinformation
the operatorsabout the onsite
working materials andstep-by-step
through equipment to be used,
protocols. the
They
contained highly-detailed information about the materials and equipment to be used, the
methodologies and working parameters, and alternative methodologies/procedures to tackle specific
conservation issues. This last was a particularly desirable requirement to improve the flexibility and
adaptivity of such instruments. The scale-up indeed required a constant check of the actual
representativity of the results of the pilot site and the methodologies implemented. In particular,
Heritage 2019, 2 809

methodologies and working parameters, and alternative methodologies/procedures to tackle specific

conservation issues. This last was a particularly desirable requirement to improve the flexibility
and adaptivity of such instruments. The scale-up indeed required a constant check of the actual
representativity of the results of the pilot site and the methodologies implemented. In particular,
there needed to be proper consideration of the increased level of complexity due to the extended
façade surfaces, the possibility that additional and unforeseen conservation issues might arise and,
consequently, thePEER
Heritage 2019, 2 FOR need for further procedures and/or for the adjustment of those already defined.
REVIEW 13
This phase therefore also required constant scientific support.
As far
As farasasthe
the managing
managing of the
of the global
global intervention
intervention is concerned,
is concerned, there isthere is connection
a strict a strict connection
between
between
the the working
technical technicalsheets
workingandsheets and theofmapping
the mapping of the intervention:
the intervention: as the formerasprescribes
the former theprescribes
modality
theeach
of modality
singularof each singular
operation, theoperation, the latter
latter provides the provides the georeferenced
georeferenced location
location for all of them.for all of them.
In Figure 11 is is reported
reported anan example
example ofof the
the mapping
mapping of thethe interventions
interventions for
for the
the façade,
façade, which
which
treatments for
includes the treatments for the
the biofilm
biofilm removal
removal andand the
the consolidation
consolidationof ofthe
thestone
stonesurfaces.
surfaces.

Figure 11.
Figure 11. (Left)
(Left) Mapping
Mapping of of the
the interventions
interventions for
for the
the biofilm
biofilm removal
removal (green color) and
(green color) and consolidation
consolidation
of the decorative elements (blue color) with references to the related technical working
of the decorative elements (blue color) with references to the related technical working sheet sheet (coded
(coded as
as T.M.S.). (Right) Photographic documentation of the additional testing and checking
T.M.S.). (Right) Photographic documentation of the additional testing and checking of the conservative of the
conservative
operation operation
conducted (a)conducted (a) on the
on the decorative decorative
elements elements
of the of the
triple-arch triple-arch
window; window;
(b) on (b) on
the Crevola the
slabs
Crevola
of slabs(c)ofduring
an ashlar; an ashlar; (c) during
cleaning of thecleaning of the cladding.
cladding.

7.
7. Conclusions
Conclusions
The
The pilot
pilot conservation
conservation site
site is
is aa suitable
suitable approach
approach toto tackle
tackle the
the inherent
inherent complexity
complexity of of the
the built
built
heritage
heritage preservation. The case
preservation. The case study
study ofof the
the Monza
Monza cathedral
cathedral demonstrated
demonstrated that
that the
the integrated
integrated and
and
multidisciplinary methodology exploited to achieve an accurate understanding of the site
multidisciplinary methodology exploited to achieve an accurate understanding of the site allowedallowed for
for the definition of effective operative procedures and the optimization of the specific parameters of
the different conservation treatments.
The state of conservation of the site was assessed by examining and mapping all the
representative decay patterns in the pilot areas, according to the different lithotypes. Consequently,
the onsite and laboratory diagnostic was effectively directed to investigate the major cause and
Heritage 2019, 2 810

the definition of effective operative procedures and the optimization of the specific parameters of the
different conservation treatments.
The state of conservation of the site was assessed by examining and mapping all the representative
decay patterns in the pilot areas, according to the different lithotypes. Consequently, the onsite and
laboratory diagnostic was effectively directed to investigate the major cause and mechanisms of
deterioration. The information gathered during the condition survey phase allowed us to set up
the guidelines for the intervention, and select and test the most suitable methodologies for each
restoration phase and substrate condition. In particular, the pilot site activity was focused on tuning and
optimizing the characteristic parameters of the defined techniques. This, in turn, increased the overall
sustainability of the procedures, as scheduling and cost-effectiveness of each phase were optimized.
As a result, the appointed conservation methodologies were effectively scaled up and
implemented in the framework of the executive conservation project. Therefore, a much more reliable
estimation of the general costs and the duration of the intervention were obtained. The final operative
tools of the pilot site activity, namely the mapping of the interventions and the technical working
sheets, were directly integrated into the final project, supported the overall planning of the operational
activities, and allowed for the assessment of the sustainability in terms of required resources.

Author Contributions: D.G. and L.T. contributed equally to conceptualization, funding acquisition, investigation,
methodology, visualization, writing, and review & editing.
Funding: The pilot site activity was supported by “Parrocchia di San Giovanni Battista-Duomo di Monza”.
Acknowledgments: Arch. Margherita Bertoldi is kindly acknowledged for the valuable collaboration during the
entire pilot site activity, the support to the on-site diagnostic, for the preparation of the thematic mappings and
the scale-up phase.
Conflicts of Interest: The authors declare no conflict of interest.

References
1. Council of Europe. Convention for the Protection of the Architectural Heritage of Europe; Council of Europe:
Strasbourg, France, 1985.
2. Dezzi Bardeschi, M. Restauro: Punto e a capo. Frammenti per una (Impossibile) Teoria; Franco Angeli: Milano,
Itaily, 2005.
3. Council of Europe. Amsterdam Charter. European Charter of the Architectural Heritage; Council of Europe:
Strasbourg, France, 1975.
4. ICOMOS. The Nara Document on Authenticity; International Council on Monuments and Sites: Paris, France,
1994.
5. Settembre Blundo, D.; Ferrari, A.M.; Fernández del Hoyo, A.; Riccardi, M.P.; García Muiña, F.E. Improving
sustainable cultural heritage restoration work through life cycle assessment based model. J. Cult. Herit. 2018,
32, 221–231. [CrossRef]
6. Turk, J.; Mauko Pranjić, A.; Hursthouse, A.; Turner, R.; Hughes, J.J. Decision support criteria and the
development of a decision support tool for the selection of conservation materials for the built cultural
heritage. J. Cult. Herit. 2018, in press. [CrossRef]
7. Rodrigues, J.D.; Grossi, A. Indicators and ratings for the compatibility assessment of conservation actions.
J. Cult. Herit. 2007, 8, 32–43. [CrossRef]
8. Revez, M.J.; Delgado Rodrigues, J. Incompatibility risk assessment procedure for the cleaning of built
heritage. J. Cult. Herit. 2016, 18, 219–228. [CrossRef]
9. Sabbioni, C.; Cassar, M.; Brimblecombe, P.; Tidblad, J.; Kozlowski, R.; Drdacky, M.; Sáiz-Jiménez, C.;
Grontoft, T.; Wainwright, I.; Ariño, X. Global Climate Change Impact on Built Heritage and Cultural Landscapes;
Taylor & Francis Ltd.: Abingdon-on-Thames, UK, 2006.
10. Nijland, T.G.; Adan, O.C.; van Hees, R.P.; van Etten, B.D. Evaluation of the effects of expected climate change
on the durability of building materials with suggestions for adaptation. Heron 2009, 54, 37–48.
11. Watt, J.; Tidblad, J.; Kucera, V.; Hamilton, R. The Effects of Air Pollution on Cultural Heritage; Springer: Berlin,
Germany, 2009.
12. Siegesmund, S.; Snethlage, R. Stone in Architecture: Properties, Durability, 5th ed.; Springer: Berlin, Germany, 2014.
Heritage 2019, 2 811

13. Doehne, E.F.; Price, C.A. Stone conservation: An Overview of Current Research; The Getty Conservation Institute:
Los Angeles, CA, USA, 2011.
14. Sandrolini, F.; Franzoni, E.; Sassoni, E.; Diotallevi, P.P. The contribution of urban-scale environmental
monitoring to materials diagnostics: A study on the cathedral of Modena (Italy). J. Cult. Herit. 2011, 12,
441–450. [CrossRef]
15. Perez-Monserrat, E.M.; Varas, M.J.; Fort, R.; de Buergo, M.A. Assessment of different methods for cleaning
the limestone façades of the former Workers Hospital of Madrid, Spain. Stud. Conserv. 2011, 56, 298–313.
[CrossRef]
16. Delgado Rodrigues, J.; Ferreira Pinto, A.P. Laboratory and onsite study of barium hydroxide as a consolidant
for high porosity limestones. J. Cult. Herit. 2016, 19, 467–476. [CrossRef]
17. Gherardi, F.; Gulotta, D.; Goidanich, S.; Colombo, A.; Toniolo, L. On-site monitoring of the performance of
innovative treatments for marble conservation in architectural heritage. Herit. Sci. 2017, 5, 4. [CrossRef]
18. Salimbeni, R.; Pini, R.; Siano, S.; Calcagno, G. Assessment of the state of conservation of stone artworks after
laser cleaning: Comparison with conventional cleaning results on a two-decade follow up. J. Cult. Herit.
2000, 1, 385–391. [CrossRef]
19. Demoulin, T.; Girardet, F.; Wangler, T.P.; Scherer, G.W.; Flatt, R.J. On-site monitoring for better selection of
stone repairs: A case study. Herit. Sci. 2016, 4, 38. [CrossRef]
20. Papayianni, I.; Stefanidou, M.; Pachta, V. Survey of repaired and artificial stones of the archaeological site
of Pella five years after application. In Built Heritage: Monitoring Conservation Management; Toniolo, L.,
Boriani, M., Guidi, G., Eds.; Springer International Publishing: Berlin, Germany, 2015; pp. 431–442.
21. La Russa, M.F.; Macchia, A.; Ruffolo, S.A.; De Leo, F.; Barberio, M.; Barone, P.; Crisci, G.M.; Urzì, C. Testing
the antibacterial activity of doped TiO2 for preventing biodeterioration of cultural heritage building materials.
Int. Biodeterior. Biodegrad. 2014, 96, 87–96. [CrossRef]
22. Delegou, E.T.; Ntoutsi, I.; Kiranoudis, C.T.; Sayas, J.; Moropoulou, A. Advanced and novel methodology
for scientific support on decision-making for stone cleaning. In Advanced Materials for the Conservation of
Stone; Hosseini, M., Karapanagiotis, I., Eds.; Springer International Publishing: Cham, Switzerland, 2018;
pp. 299–324.
23. Gherardi, F.; Goidanich, S.; Toniolo, L. Improvements in marble protection by means of innovative
photocatalytic nanocomposites. Prog. Org. Coat. 2018, 121, 13–22. [CrossRef]
24. Raneri, S.; Barone, G.; Mazzoleni, P.; Alfieri, I.; Bergamonti, L.; De Kock, T.; Cnudde, V.; Lottici, P.P.;
Lorenzi, A.; Predieri, G.; et al. Efficiency assessment of hybrid coatings for natural building stones: Advanced
and multi-scale laboratory investigation. Constr. Build. Mater. 2018, 180, 412–424. [CrossRef]
25. Roveri, M.; Gherardi, F.; Brambilla, L.; Castiglioni, C.; Toniolo, L. Stone/coating interaction and durability of
Si-based photocatalytic nanocomposites applied to porous lithotypes. Materials 2018, 11, 2289. [CrossRef]
[PubMed]
26. Ban, M.; Mascha, E.; Weber, J.; Rohatsch, A.; Delgado Rodrigues, J. Efficiency and compatibility of selected
alkoxysilanes on porous carbonate and silicate stones. Materials 2019, 12, 156. [CrossRef] [PubMed]
27. Moropoulou, A.; Delegou, E.T.; Avdelidis, N.P.; Koui, M. Assessment of cleaning conservation interventions
on architectural surfaces using an integrated methodology. MRS Proc. 2002, 712, II2.5. [CrossRef]
28. Charola, A.E.; Centeno, S.A.; Normandin, K. The New York Public Library: Protective treatment for sugaring
marble. J. Archit. Conserv. 2010, 16, 29–44. [CrossRef]
29. Sassoni, E.; Graziani, G.; Franzoni, E. Repair of sugaring marble by ammonium phosphate: Comparison
with ethyl silicate and ammonium oxalate and pilot application to historic artifact. Mater. Des. 2015, 88,
1145–1157. [CrossRef]
30. Dreyfuss, T. Interactions on site between powdering porous limestone, natural salt mixtures and applied
ammonium oxalate. Herit. Sci. 2019, 7, 5. [CrossRef]
31. Cassanelli, R. Monza anno 1300. La Basilica di S. Giovanni Battista e la sua Facciata; Comune di Monza: Monza,
Italy, 1988.
32. ARPA-Lombardia. Available online: www.arpalombardia.it/sites/QAria (accessed on 1 February 2019).
33. ICOMOS. Principle for the Analysis, Conservation and Structural Restoration of Architectural Heritage;
International Council on Monuments and Sites: Paris, France, 2003.
Heritage 2019, 2 812

34. UNI 11182:2006. Cultural heritage. Natural and artificial stone. Description of the alteration. Terminology
and definition. Ente Italiano di Normazione, 2006. Available online: https://infostore.saiglobal.com/en-au/
Standards/UNI-11182-2006-1071699_SAIG_UNI_UNI_2497752/ (accessed on 1 February 2019).
35. EN 16096:2012. Conservation of Cultural Property—Condition Survey and Report of Built Cultural Heritage;
European Committee for Standardization, 2012. Available online: https://infostore.saiglobal.com/preview/
is/en/2012/i.s.en16096-2012.pdf?sku=1566979 (accessed on 1 February 2019).
36. ICOMOS. Principles for the Recording of Monuments, Groups of Buildings and Sites; International Council on
Monuments and Sites: Paris, France, 1996.
37. Letellier, R. Recording, Documentation and Information Management for the Conservation of Heritage Places.
Guiding Principles; The Getty Conservation Institute: Los Angeles, CA, USA, 2011; Volume 1.
38. Campanella, C. II Rilievo Degli Edifici: Metodologie e Tecniche per il Progetto di Intervento; Flaccovio: Palermo,
Italy, 2017.
39. ICOMOS. Illustrated Glossary on Stone Deterioration Patterns; International Council on Monuments and Sites:
Paris, France, 2008.
40. Gulotta, D.; Villa, F.; Cappitelli, F.; Toniolo, L. Biofilm colonization of metamorphic lithotypes of a renaissance
cathedral exposed to urban atmosphere. Sci. Total Environ. 2018, 639, 1480–1490. [CrossRef] [PubMed]
41. Gulotta, D.; Bontempi, E.; Bugini, R.; Goidanich, S.; Toniolo, L. The deterioration of metamorphic
serpentinites used in historical architecture under atmospheric conditions. Q. J. Eng. Geol. Hydrogeol.
2017, 50, 402–411. [CrossRef]
42. Toniolo, L. New trends and related problems in stone cleaning and conservation. In New Trends in Analytical,
Environmental and Cultural Heritage Chemistry; Colombini, M.P., Tassi, L., Eds.; Transworld Research Network:
Kerala, India, 2008; pp. 256–276.
43. Doherty, B.; Pamplona, M.; Selvaggi, R.; Miliani, C.; Matteini, M.; Sgamellotti, A.; Brunetti, B. Efficiency and
resistance of the artificial oxalate protection treatment on marble against chemical weathering. Appl. Surf. Sci.
2007, 253, 4477–4484. [CrossRef]

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution
(CC BY) license (http://creativecommons.org/licenses/by/4.0/).