Subfloor Preparation Guide

Subfloor Preparation Guide

INTRODUCTION Some severe conditions cannot be corrected by normal

preparation techniques and the only remedy may well be to uplift
Surface preparation is a vital part of any contract. Improper or and relay the complete subfloor.
inadequate preparation can cause premature failure of the system.
It is the intention of this Subfloor Preparation Guide to describe Any substrate forming the base on which an F. Ball product is
the different types of procedures available to produce the most applied should be designed to withstand all structural, thermal and
acceptable substrate possible, ready for the installation of one or mechanical stresses and loads which will occur during service. A
more of our products. substrate should remain stable and be provided with any
expansion, contraction and crack inducement joints necessary.
All aspects of subfloor preparation and floorcovering installation Cracking, unevenness and faults in the substrate may be reflected
should be in accordance with the appropriate standard. During the through the surface treatments and floorcoverings. It must be
laying of the floorcovering a temperature of at least 18°C must be acknowledged that any shortcomings or failures in a subfloor
maintained along with a floor temperature of at least 10°C. The could lead to a premature failure.
type and condition of the subfloor has a direct influence on the
installation and performance of a floorcovering and the REFERENCES
importance of subfloor preparation cannot be emphasised too
strongly. Before the final treatment to bring a subfloor up to the The following British Standards should be referred to when
standard required for the application of floorcoverings can begin, specifying and installing F. Ball products or systems: BS8204 code
the condition of the base must be investigated and any necessary of practice for concrete bases to receive in-situ floorings.
treatments or repairs carried out. BS8203 the installation of resilient floorcoverings.
BS5325 the installation of textile floorcoverings
BS8201 the installation of timber and timber based products.

SUBSTRATES

Good design and subsequent installation practices to receive

F. Ball products or systems are essential for the success of the
finished floor. In order to minimise problems and save possible
additional costs, it is essential that specifiers, clients, main
contractors or installers of subfloors such as concrete and sand
cement screeds, should have tested and be satisfied that the
surfaces are to specification and adequate for the intended use.

The company recommends the procedures mentioned in this

leaflet for the preparation of concrete, screeds and other surfaces
prior to the installation of our products. This information is
primarily concerned with floors although general information can
be extracted in the case of vertical surfaces but extra
consideration should be shown due to possibly greater
absorbency of many of the surfaces i.e. brick, blockwork, plaster,
etc. Obviously vertical surfaces do not usually have to withstand
Certain systems may be ‘tolerant’ to lower standards of the same degree of wear and tear that horizontal surfaces are
preparation, but lower standards should not be accepted without subjected to. Coverage rates of materials may be affected by the
careful consideration of their implications i.e. the increased selected method of surface preparation and due allowances made
potential for premature failure which is counter productive and for any increase or decrease.
expensive to rectify. Where application involves questionable
substrates the installer must exercise extreme caution and advise
the client of the attendant risks involved. Old or new substrates
contaminated with oil, grease, fat or chemicals, faulty concrete,
inferior grades of concrete, floors with large cracks or crevices,
poor asphalt and tiles are not satisfactory bases for our products.
CONSIDERATIONS – OLD CONCRETE major cause of dusty and damaged concrete floors. Failure to
AND SCREED SURFACES remove it may lead to failure of the surface treatment smoothing
underlayments. Unless it has been removed by previous surface
Old or screeded surfaces are often contaminated, worn or preparation techniques, laitance may still be present on old
degraded. They often present a greater risk than new substrates. concrete and screeded floors. Removal is vitally important.
BS8204 should be used as a guide to good flooring methods. In
order to minimise problems and save additional costs, it is
essential that specifiers, clients, main contractors or installers of SURFACE PREPARATION TECHNIQUES
F. Ball systems on old concrete bases and screeds have the floor
tested, and are satisfied that surfaces are adequate for the The most frequently used methods of surface preparation of
intended use. A surface tensile pull-off strength of at least concrete or screeded floors are:
1.5 N/mm2 onto a prepared subfloor is required before the
application of further underlayments and serves as a good guide (i) Dust-free grit blasting
as to the integrity of the floor. (ii) Mechanical planing
(iii) Scabbling
The depth and type of contamination should be checked to (iv) Grinding
ensure that removal and subsequent adhesion can be ensured. It (v) Abrading
is often advisable to take cores from the most contaminated areas
to be sure of penetration depth of contamination and the This leaflet describes the main advantages and disadvantages of
soundness of substrate. For instance, oil can penetrate many each method. Floors and their uses vary enormously. Therefore,
centimetres into concrete, and although the surface may be each method must be judged on its merits and full account be
cleaned, it can migrate back to the surface. Adhesion of a DPM, taken of the working environment in which the preparation has to
underlayment or adhesive may be compromised or in the worst take place. For example, scabbling may be a perfectly suitable
cases be non existent. If in doubt, do not progress any further method of preparing a floor in an unoccupied site. However, the
without management instructions. Further discussion with our resulting dust and noise may preclude it in many other situations.
Technical Services Department may be advisable before
proceeding. DUST-FREE GRIT BLASTING
This is the fastest and most efficient form of old and new floor
preparation and laitance removal, available to date. The machines
LAITANCE used vary in size and are generally operated by specialist concrete
preparation contractors or flooring contractors. Horizontal and
Laitance is always present on new concrete bases and screeds and slightly inclined surfaces are impacted and abraded by steel
should be removed. Laitance is formed from a mixture of water, abrasive propelled at high velocity by the machine. At the same
cement and the fine particles of the screed or concrete mix that time the abrasive grit and resultant debris is contained and
is brought to the surface when placing and trowelling up. As the reclaimed by powerful suction processes. The grit is cleaned and
concrete or screed cures this mixture dries to form a crust or recycled for immediate re-use. The abrasive grit and debris is
thin layer, known as laitance on the surface. The wetter the mix, deposited in environmentally safe containers by the machine
and the more it is worked or trowelled, the thicker and usually the whilst it is working. Up to 1000m2 of flooring may be completed
weaker the laitance will be. The thickness of laitance may vary in a day. This is a dry process, and floor laying may often continue
from, in the best cases, barely measurable – to the worst whilst preparation is progressing in adjacent areas. In many cases old
examples, 6mm or more. Scoring the surface with a steel edge (i.e. coatings and other contamination may be removed by this method.
a screwdriver) until the main aggregate in the mix is reached will
determine the thickness of the laitance. Dust-free grit blasting is far quicker, quieter and cleaner than
mechanical planing, scabbling, etc. The disadvantage is the general
Laitance has relatively poor adhesion to the mass of the aggregate inability of the machine to remove exceptionally thick, hard or
in the mix. It is friable and weak in comparative strength, and can flexible materials i.e. certain epoxy or polyurethane floor surfaces.
therefore either delaminate under traffic conditions and impact or The specialist contractor using these machines will advise in more
it may easily dust away under abrasion from traffic. Therefore, the detail.
new floor surface needs to be bonded to the mass of the
aggregate in the base on which it is laid. The heavier the use of MECHANICAL PLANING
the floor, and the greater the temperature fluctuations that the Often referred to as ‘concrete planing’ the machines use carry
floor is subjected to, the more important this is. Laitance is a rows of rotating cutters tipped with tungsten. The removal of
laitance and other forms of surface contamination are excellent. All laitance and any other form of contamination should be
The profile left by the machine is dependent on the spacing and removed by the most appropriate technique.
type of cutters installed by the operator. The surface may be
grooved or flat. Surfaces are more roughened than dust-free grit Immediately prior to applying any coating, topping or adhesive,
blasting. Greater thicknesses of the substrate can be removed ensure that dust from any preparation method employed is
more quickly and effectively than by grit blasting. removed by vacuuming wherever possible. Preparing concrete
may be a dusty operation. Masks and good ventilation should be
Mechanical planing is slower, noisier and nearly always very dusty. provided. Protection of walls, furniture and equipment should be
The addition of vacuum suction cleaners to these machines does planned.
help to reduce dust, but seldom eliminates it.
Residues or spillages of other trades such as plaster, paint, cement,
SCABBLING oil and sometimes roofing tar are frequently present in new
This is a heavy-duty method of preparing concrete frequently seen constructions, and should be removed. Plaster and cement can be
on concrete motorways. Scabbling tools are driven by chipped up and wire brushed. Paint should be mechanically
compressed air and the tool head is tipped with tungsten. The removed. Oil must be removed by washing with a water
tool works by vibrating and impacting the surface of the concrete, emulsified degreaser. Hot compressed air and epoxy sealing can
thus shattering the surface as it works. This system is not suitable sometimes be used for badly affected areas, alternatively the
for preparation if the floor system being applied is less than 10mm substrate should be replaced. Oil will affect adhesion of the floor
(please consult our Technical Department for further advice). smoothing underlayment and adhesive. In certain circumstances
the presence of oil may stain the new decorative floorcovering. If
Scabbling is a slow, very dusty, very noisy and dirty process. On water flows under partitions, walls, cover mouldings, equipment
certain surfaces it has the disadvantage that it can damage the bases or furniture, these areas will take longer to dry out and may
concrete or screed to the degree that it weakens the substrate delay the installation. Putting paper or polythene sheet on the
too much. This process is now less frequently used for internal floor to keep it clean retards the drying.
work on floors.
If old concrete has never been overlaid or painted it should be
GRINDING treated the same as new concrete. More emphasis must be placed
Grinding is usually carried out by machines used for polishing on cleaning, and repairing any cracks, holes or eroded areas.
terrazzo floors. It is a useful method of preparing a level floor to Often the best procedure is to remove all contaminated and
remove laitance and expose the aggregate in a substrate. unsound concrete.

ABRADING Oil, fats and grease are best removed by steam cleaning, using a
There are a number of methods of abrading which include the use good detergent, or by hot compressed air blasting and further
of STR machines, corundum blocks, or using abrasive papers, etc. treatment with a special primer. Animal fats cannot be removed
These have their limited uses and are not generally used on larger by washing. If such contaminants have penetrated into the surface
areas. (which is usually the
case) the only way
FINAL CHECKS of removing them is
Hardeners and surface membranes frequently interfere with mechanically. This
adhesion and should have been removed by the surface means dust-free grit
preparation method used. blasting, scarifying,
or scabbling or hot
Before coating or topping, concrete or screeds must be: free of all compressed air
contamination and laitance; strong enough to support the coating blasting. Remedial
or topping under the conditions for which the floor is designed. work in meat
Concrete and sand/cement screeds must be left for construction processing and
moisture to dry out before floorcoverings are laid. Readings engineering plants,
greater than 75% RH should be treated with STOPGAP F75 or for example,
F76 surface damp proof membranes, following preparation of the remains a very difficult problem. Usually removing the
concrete or sand/cement screed detailed within this document. contaminated concrete and re-screeding may be the only solution.
STOPGAP ISOLATOR can be used in certain situations as a fast Cores should always be taken to determine the depth of
track alternative for damp floors. penetration of the contamination. Cores assist in reaching a
decision whether it is possible or not to prepare a surface for prevent moisture escaping. In both cases adhesion will be
overlaying. It may be necessary to carry out adhesion tests to impaired if a water based smoothing underlayment or adhesive is
ensure adequate adhesion to a contaminated surface. applied. The substrate should be prepared by mechanical means
such as Grit blasting. If a waterproofing admixture is known to
If necessary, repairs to have been used, further testing should be carried with the
damaged floors should proposed system to ensure complete compatibility and adhesion
be carried out using to the host substrate.
products such as
STOPGAP 400 prior to Some acrylic based curing agents may be overcoated with certain
applying smoothing STYCCOBOND adhesives and advice should be sought from the
compounds (please Technical Services Department before proceeding. If in doubt
contact our Technical always mechanically prepare the surface
Services Department
for further details). Surface Damp Proof Membranes
The specific concrete Membranes such as STOPGAP F75 or F76 can be overcoated with
patching material must smoothing underlayments or certain adhesives. When applying a
be checked for compatibility with the surfacing system and be of smoothing underlayment onto a damp proof membrane, the
suitable strength for the usage of the finished floor. surface should be primed with neat STOPGAP P131 and allowed
to dry before proceeding with the underlayment. STOPGAP 100
may be applied directly. Adhesives such as STYCCOBOND F41
NON ABSORBENT SURFACES and F46 can be applied direct to STOPGAP F75 or F76.
Please refer to the data sheets or Technical Services Department
Surfaces that will not allow the passage of water to pass through for further information on these products.
them can be regarded as non-absorbent. Surfaces such as ceramic
and quarry tiles, granolithic, terrazzo, paints and to some extent Asphalt
power floated concrete can all come under this heading. Providing the flooring grade asphalt is in good condition, sound,
strong enough and has not suffered rutting or any other sign of
Coated Surfaces softening and is free from any form of contamination, then the
Traditional floor paints such as those based on oil or acrylic surface should be cleaned with STYCCOCLEAN C140, rinsed
emulsions should be removed. Epoxy or polyurethane paints can with clean water and allowed to dry. The surface should then be
be overcoated providing they are in good condition and well primed with neat STOPGAP P131, allowed to dry followed by
adhered to the substrate. Coatings vary considerably in this 3mm of the appropriate STOPGAP smoothing underlayment.
respect and we would suggest you check adhesion by prior testing
to ensure a satisfactory bond is achieved. The coating should be Ceramic,Terrazzo and Quarry Tiles
cleaned using Styccoclean C140 then either primed with neat Providing these are sound and no cracks or elevated tiles are
STOPGAP P131 followed by the recommended smoothing present, these should be cleaned to remove all traces of
underlayment or the adhesive applied direct to the paint (please contamination such as polish etc, then primed with neat
contact our Technical Services Department for further STOPGAP P131, allowed to dry then skimmed with a minimum
information on product selection). However, in the majority of 3mm of the appropriate STOPGAP smoothing underlayment.
cases identifying the type of paint or coating will be difficult and it Heavily glazed surfaces should be mechanically prepared by shot
is most likely it will be brittle, worn, peeling or flaking off the blasting, or grinding with a coarse abrasive to aid adhesion before
substrate and is therefore not good enough to receive either priming.
smoothing underlayment or adhesive. The easiest method of Terrazzo and Quarry tiles are unaffected by dampness but may be
removing old paint is usually dust-free grit blasting. Note certain sufficiently permeable to allow the passage of moisture vapour
paints and coatings may allow the passage of moisture to pass and are often laid in areas which do not incorporate a damp proof
through them and checks should be made for moisture before membrane.Where this is the case, these bases should be covered
progressing further work. with a layer of flooring grade asphalt complying with BS6925.
Alternatively the use of a surface DPM such as STOPGAP F75 or
Chemical Hardening and Waterproofing Admixtures and F76 can be applied providing the substrate has been sufficiently
Curing Agents prepared by mechanical means and the grout lines raked out. In
All these products are designed to generally repel water from both cases this should be followed by priming with neat
entering into the concrete or screed or to form a barrier to STOPGAP P131 and allowed to dry before applying 3mm of the
appropriate STOPGAP smoothing underlayment. If either method and a high strength smoothing underlayment applied such as STOPGAP
is not possible, lift the tiles and relay the floor. 100, 200 or 300 followed by the recommended adhesive.

STOPGAP ISOLATOR may also be used under certain situations. Any remaining adhesive on wooden floors should be overpinned
Note: Old installations may involve the substrate consisting of Ash, with flooring grade plywood or hardboard and thoroughly
which can become unstable if covered up. Checks should be carried out secured at 100-150mm centres (see wooden floors). Any existing
to establish the integrity and make up of the substrate. underlayments should be removed.

EXISTING FLOORCOVERINGS

Most floorcoverings such as flexible vinyl, linoleum and textile

floorcoverings must be removed and the substrate thoroughly
prepared before fully bonded floorcoverings can be laid. Some
vinyl or similar type floor tiles can be overcoated providing they
are firmly bonded to the subfloor and all traces of polish or any
other contaminant which would prevent good adhesion are
removed e.g.With Styccoclean C140 Floor Cleaner. If this cannot
Power Floated Concrete Slabs be achieved then the tiles must be removed, and the substrate
These should be treated in the same way as traditional concrete suitably prepared.
and sand/cement screeds. In some cases it is possible to use a
pressure sensitive or tackifier adhesive such as F46 or F41 direct Note. Certain vinyl tiles were made using asbestos, and
to the power floated slab providing the moisture content of the professional advice should be taken before proceeding to remove
slab is below 75% RH. Checks should be made with our Technical these types of tile.
Service Department before proceeding. Generally with older building, these types of tiles were often laid
on floors that did not contain a DPM.
Note: 1. Most power floated slabs will be cured with a curing agent. In
most cases this will be acrylic based, however, wax based curing agents
or certain silicate based products may be present and will inhibit the COMPOSITION FLOORS
bond performance and these should be removed by mechanical means
such as grit blasting. Floors constructed of magnesium oxychloride cement or
2. Power floated concrete slabs especially those cured with curing polyvinyl acetate/cement will be adversely affected by dampness
agents will take a considerable amount of time to dry and the use of rising form the ground if they are covered with an impervious
epoxy damp proof membranes such as STOPGAP F75 or F76 should be layer. Unless it can be established that the composition floor is
used if a fast track floor installation is required. adequately protected against rising dampness, it must be removed
and the base made good before floorcoverings are installed. If the
Adhesive Residues floor is protected against dampness then cracks and small hollows
Any old adhesive residues should be removed by mechanical should be patch filled and the whole area skimmed with a
methods such as scraping, grit blasting and grinding etc. Certain minimum 3mm of the appropriate STOPGAP smoothing
underlayments are able to cope with only minimal traces of firmly underlayment.
adhered and hard adhesive residues (not water soluble). At least
75% of the floor area should be clean.This will be followed by the
application of neat STOPGAP P131, allow it to dry and then CALCIUM SULPHATE SCREEDS
proceed with the appropriate STOPGAP smoothing
underlayment. Please refer to our Technical Service Department In all cases, Calcium Sulphate screeds that include, Anhydrite and
for product selection. Alpha Hemihydrate type screeds should be sound smooth and
dry. All laitance should be removed during the initial grinding
Note: 1. If in doubt remove all traces of adhesive residues back to a stage, however, this is not always the case and checks should be
sound and well-prepared substrate. made prior to proceeding with the application of any material. If
2. Highly trafficked areas and those subject to high temperatures such laitance should still exist, this should be mechanically removed by
as conservatories, should be mechanically prepared to remove all further grinding/sanding and the dust fully vacuumed off. It is
adhesive residues, primed with dilute STOPGAP P131, allowed to dry imperative that checks are also made to determine the moisture
content of the floor and this is carried out using a Hygrometer in RAISED ACCESS MODULAR FLOORS
accordance with BS8203. A reading of less than 75%RH must be
obtained before priming using STOPGAP P121 and allowing to These are designed to give ready access to underfloor services.
dry before the application of the appropriate STOPGAP All modular units must be structurally sound, level, smooth and
smoothing underlayment or STYCCOBOND adhesive. free from contaminants. New floors should be degreased using
STYCCOCLEAN C141 and allowed to dry before placing the
adhesive. Backed carpet tiles secured with an tackyfying adhesive
WOODEN FLOORS such as STYCCOBOND F41 are is suitable for this type of base.
Broadloom carpets are not suitable in this type of situation.
All wooden floors must be structurally sound, level, smooth, dry
and clean. Adequate ventilation should be provided to suspended
timber floors at ground level to ensure that the moisture content CONCLUSION
of the wood is maintained at equilibrium. Worn or uneven
floorboards should either be replaced or levelled by sanding, It must be appreciated that these recommendations are of
planning or by patch filling with STOPGAP GREEN BAG/114 latex necessity in a general nature. Modifications may be required
underlayment before finally covering with flooring grade plywood. according to the floor system used and the service conditions
Sheets should be positioned, joints staggered and nailed at under which the surface has to adequately perform. If there is any
100 – 150mm centres. (See BS8203 for details). doubt seek further advice from our Technical Services
Department before proceeding with the application of our
Wood blocks are not suitable for direct application of sheet or tile products. The company will be pleased to check advice given by a
flooring because of the continuous differential movement of the contractor or applicator of F. Ball products. However, because we
blocks and the risk of the wood block design transferring through may be unaware of every situation where our products are
the floorcovering surface. Provided the wood blocks are smooth, supplied, it is impossible to check all sites where F. Ball materials
sound, level and securely bonded, they should be overlayed with are used. This leaflet is therefore to be used only as an informed
flooring grade plywood. Any uneven areas should first be patch guide to floor preparation methods. The responsibility for the
filled with STOPGAP GREEN BAG/114 latex smoothing preparation of any substrate must remain with the installer.
underlayment. Wood blocks laid on the ground floors must have Because of the wide variety and uses of our materials, the
an efficient damp proof membrane incorporated in the subfloor. If Company is always more than willing to offer help and assistance
there is any doubt whether these conditions can be met, then the with individual flooring problems (please contact our Technical
wood blocks must be removed and the subfloor made good with Services Department for further advice).
flooring grade asphalt or a modified sand cement screed
incorporating an effective damp proof membrane. The detail in this information sheet is given in good faith, and is
based on results gained from experience and tests. However, all
Wood mosaic panels require overpinning with flooring grade recommendations or suggestions are made without guarantee,
plywood in all cases.This is not practical on solid floors and panels since the conditions of use of the floor and the placement of
should therefore be removed. materials are beyond our direct control.

To ensure this information is correct, please contact our Technical

If panels laid over a flexing timber floor need patch filling, Service Department (see reverse).
STOPGAP GREEN BAG/114 latex smoothing underlayment
should be used. In all other respects wood mosaic panels should
be treated as for wood block.

Chipboard should comply with BS5669 flooring grades, type, C2,

C4 or C5. It is essential that floating chipboard and other
composition floors are dry, as a gully may develop between the
skirting board and the edge of the floorcovering as the boards
shrink on drying.

In all cases Chipboard, plywood and hardboard must be primed

with dilute STOPGAP P131 or STOPGAP F70 as recommended.
 For further information about F. Ball products or
technical advice please contact:

Churnetside Business Park

Station Road
Cheddleton
Leek
Staffordshire
ST13 7RS United Kingdom

Tel: +44 (0) 1538 361633

Fax: +44 (0) 1538 361115
Technical Services Fax: +44 (0) 1538 361567
Email: marketing@f-ball.co.uk

and/or

F. Ball and Co. (Asia) Pte Ltd

18 Toh Guan Road East
Block 12 #03-01
Singapore 608591

Tel: +65 6515 1715

Fax: +65 6515 1738
Email: mail@f-ballasia.com

www.f-ball.co.uk