Panel Guide

Version 4
Annex 2F: Wet process Wet process fibreboards can be classified according to
their density:
fibreboards
Description • Hardboards ≥900 kg/m3
A wood fibre board (fibreboard) is defined as a panel • Medium boards* ≥400 kg/m3 to <900 kg/m3
material with a nominal thickness of 1.5mm or greater, • Softboards ≥230 kg/m3 to <400 kg/m3
manufactured from lignocellulose fibres with application
of heat and/or pressure. This generic product type ‘fibre- *Mediumboard (which should not be confused with
boards’ can be classified according to the production Medium Density Fibreboard – MDF) can be sub-divided
process and in this regard there are two classifications: into:

• Wet process fibreboards • Low density mediumboard 400 kg/m3 to <560 kg/m3
• Dry process fibreboards (MDF). • High density mediumboard 560 kg/m3 to <900 kg/m3

Dry process fibreboard (MDF) is described separately in Composition and manufacture

Annex 2E of PanelGuide. Wet process fibreboards can be made using either
softwood or temperate hardwood species (or both) (some
low density mediumboards are made from recycled
paper fibre). Wood chips are thermally softened in water
and then mechanically refined into fibres. The wet fibres
are formed into a mat which is either rolled (softboards),
or rolled and then pressed, at a high temperature to the
desired thickness. The primary bond is generally derived
from the felting together of the fibres and their inherent
adhesive properties, although in some instances a
synthetic adhesive may be added to the fibres. Other
additives such as wax, bitumen emulsion, natural oil or
fire retardant chemicals may also be added.

The differentiating feature between a wet process and

dry process fibreboard is that wet process fibreboards
Figure A2.7: Hardboard have a fibre moisture content of more than 20% at the
forming stage whereas dry process fibreboards have a
fibre moisture content of less than 20% at the forming
stage and they are produced with the addition of a
synthetic resin binder.

There is currently no UK production of wet process fibre-

boards.

Appearance
Hardboard
Surface appearance of hardboards is usually smooth on
Figure A2.8: Mediumboard
one side and a fine mesh pattern on the reverse. Duo
faced hardboards (smooth both sides) are also available.
The colour of panels ranges from light gold to dark
brown. Special panels are available including painted,
plastic faced, printed with wood grain, embossed/
textured (plain, primed or pre-decorated) and perfo-
rated. Enhanced strength and durability characteristics
may be imparted by impregnation with hot oil or resin
and subsequent heat curing; these panels are usually
referred to as tempered hardboard.

Mediumboard
The surface texture is usually smooth on one side with
a fine mesh pattern on the reverse. High density medi-
umboard usually has a hard, shiny surface whereas
low density mediumboards have a matt surface. Colour
Figure A2.9: Softboard ranges from mid grey to dark brown.

PanelGuide (V4) Annex 2F 1

Softboard Enhanced performance hardboards can be used for
The surface texture for unfaced natural panels is open applications where higher strength properties and resist-
and fibrous. Paper-faced or fine pulp overlaid softboards ance to abrasion above that of standard hardboard is
have smooth or lightly dimpled faces, or a slight mesh required. These panels find applications as components
pattern on one or both sides. The colour of most panels within structural members such as custom-made beams,
is various shades of light brown, others are cream or exterior applications such as soffits and signage, and for
off-white. Some panels are covered with a white primer uses in packaging, agriculture and flooring overlays.
or bleached pulp for painting. Softboards with enhanced
durability and moisture resistance are produced. Mediumboards
Currently these enhanced properties are imparted by Low density mediumboards have particular application
impregnating the fibres with a bitumen emulsion; a as pinboard and as components of partitioning systems.
spray coating on one or both surfaces may also be They can also be found in shopfitting and display appli-
applied. The same characteristics can be imparted with cations and as a floor underlay material. High density
the inclusion of phenolic resins. Typical bitumen impreg- mediumboards have been used as wall and ceiling lining
nated panels are dark brown to black in colour. panels and as a sheathing material in timber frame
construction; however, their use today in UK construc-
Density, mass and panel size tion is limited.
Panel density and the panel mass varies according to the
product, being affected by the timber species and the Softboards
process used in manufacture. Like mediumboards, the range of applications for soft-
boards today has diminished; however, they do find
application as pinboard, underlay materials and as
• Softboard – densities range typically from 230 kg/m3
an acoustic absorbent. Impregnated softboards have
to 400 kg/m3. A 2400mm × 1200mm × 13mm panel
been used as a sheathing material in timber frame
will weigh approximately 10kg.
construction and as a protective overlay in some forms
• Mediumboard – low density: densities vary
of flat roofing. In pitched roof construction in Scotland,
typically from 400 kg/m3 to 560 kg/m3. A
impregnated softboards are used as a sarking material
2400mm × 1200mm × 6.4mm panel will weigh
and heavily impregnated brands find application as joint
approximately 10kg.
fillers.
• Mediumboard – high density: densities vary
typically from 560 kg/m3 to 900 kg/m3. A
2400mm × 1200mm × 6.4mm panel will weigh Specification
approximately 15kg. Wet process
Fibreboards manufactured in Europe must now be
• Hardboard – densities vary typically from 900 kg/m3
specified in accordance with European Standards. The
to 1100 kg/m3. A 2400mm × 1200mm × 3.2mm panel
will weigh approximately 9kg. UK versions of these are BS EN 622 Parts 1 to 4. As
explained in PanelGuide Section 2, fibreboards used in
Panel sizes construction must comply, (by law) with the require-
Typical panel sizes are shown in Table A2.29. ments of the Construction Products Regulations (CPR)
by compliance with the harmonised European standard
Other sizes are available or can be produced to order. for wood-based panels (BS EN 13986).

Table A2.29: Wet process fibreboard panel sizes This standard calls up the following parts, relating to
wet process fibreboards:
Panel type Thickness Typical sizes mm
range mm
Hardboard 1.2 to 9.5 1220 × length up to 3660 • BS EN 622-1 Fibreboards. Specifications. General
requirements1
Mediumboard 6.0 to 12.0 1220 × lengths up to 3660
Softboard 8.0 to 25.0 600 to 1220 × lengths up to 3660
• BS EN 622-2 Fibreboards. Specifications.
Requirements for hardboards2
• BS EN 622-3 Fibreboards. Specifications.
Applications Requirements for medium boards3
Wet process fibreboards find use in a wide range of • BS EN 622-4 Fibreboards. Specifications.
construction and furniture related applications. Requirements for softboards4

Hardboards Selection of a grade of panel is dependent upon the

Hardboards are used in furniture as drawer bottoms and ambient climatic conditions together with the level of
unit backs, as door facings, caravan interiors and floor loading that is anticipated (see Table A2.30).
coverings, as well as in shopfitting and display work.
Standard hardboard is generally not recommended for Guidance on the selection of different grades of fibreboard
exterior use or for use in areas subject to direct wetting is given in tabular format in PanelGuide Sections 2.4 to
or high humidity conditions. 2.14; additional selection guidance is given in DD CEN/

PanelGuide (V4) Annex 2F 2

Table A2.30: Types and grades of wet process wood fibreboard

Panel type Grade References

Softboard
General purpose (for use in dry conditions) SB
General purpose (for use in humid conditions) SB.H
General purpose (for use in exterior conditions) SB.E BS EN 622-4
Load bearing (for use in dry conditions) SB.LS
Load bearing (for use in humid conditions) SB.HLSa
Low density mediumboard
General purpose (for use in dry conditions) MBL
General purpose (for use in humid conditions) MBL.H BS EN 622-3
General purpose (for use in exterior conditions) MBL.E
High density mediumboard
General purpose (for use in dry conditions) MBH
General purpose (for use in humid conditions) MBH.H
General purpose (for use in exterior conditions) MBH.E
Load bearing (for use in dry conditions) MBH.LA1 BS EN 622-3
Heavy duty load bearing (for use in dry conditions) MBH.LA2
Load bearing (for use in humid conditions) MBH.HLS1a
Heavy duty load bearing (for use in humid conditions) MBH.HLS2a
Hardboard
General purpose (for use in dry conditions) HB
General purpose (for use in humid conditions) HB.H
General purpose (for use in exterior conditions) HB.E BS EN 622-2
Load bearing (for use in dry conditions) HB.LA
Load bearing (for use in humid conditions) HB.HLA1
Heavy duty load bearing (for use in humid conditions) HB.HLA2
a These panels are restricted under humid conditions to instantaneous or short periods of loading

TS 12872. The requirements specified in BS EN 622 are General guidance on the use of preservative treatments
not specific to any particular application. for panel products can be found from the WPA Manual
Industrial wood preservation specification and practice.
Physical properties Commodity Specification C11. This guidance assists
Climate with making the right choice of preservatives for the end
Like other wood-based panel products, fibreboards are use and the panel product to be treated, as not all panel
hygroscopic and their dimensions change in response to products need to be treated for particular end uses or are
changes in humidity. Typically a 1% change in moisture indeed suitable for some treatments. It also stresses that
content results in an equivalent change of 0.4mm per the preservative and/or the panel manufacturer should
metre in length and width of the panel. As a guide, be consulted before any treatment is carried out as
wood fibreboard can be expected to attain the following treatment may alter the physical and/or visual properties
moisture content under the conditions specified in of the panel product.
Table A2.31.

Table A2.31: Expected moisture content of wood fibreboard

Water vapour permeability
The value of water vapour resistance factor (m) for fibre-
Relative humidity at 20ºC Approximate equilibrium moisture
content
boards varies according to density (Table A2.32). Water
vapour resistance factors are given as dry cup and wet
30% 5%
cup values according to BS EN ISO 12572.
65% 8%
85% 12%
Table A2.32: Water vapour resistance factor (µ) for fibreboards
The values given are extracted from BS EN 13986
Biological attack Wood-based panel Density Vapour resistance factor
Fibreboards will not normally be attacked by wood- kg/m3 Wet cup µ Dry cup µ
boring insects in a temperate climate. Panels intended
Fibreboard BS EN 622 250 2 5
for internal uses are susceptible to fungal attack under
prolonged wet conditions. Some types of hardboard and 400 5 10
bitumen impregnated softboard (>25% impregnation) 600 12 20
have been shown to have improved durability against 800 20 30
wet rot fungi, over standard grades.

PanelGuide (V4) Annex 2F 3

Table A2.33: Thermal conductivity (λ) of fibreboards Storage and handling
The values given are extracted from BS EN 13986
Fibreboards should be stored flat and dry, off the ground,
Wood-based panel Density Thermal conductivity λ with all four edges flush. Storage in an enclosed building
kg/m3 W/(m.k) is preferable and external storage should be avoided.
Fibreboard BS EN 622 250 0.05 Stacking on edge should also be avoided wherever
400 0.07 possible. Panels should be stacked on a close-boarded
600 0.10 or slatted pallet, or if this is not possible on battens at
800 0.14 no more than 600mm centres. The battens should all be
of equal thickness and should be vertically aligned with
Thermal conductivity any others in the same stack, in order to avoid distortion
The thermal conductivity of fibreboards (l) varies of the panels.
depending on density (Table A2.33).
Panels should be protected by a waterproof covering
Reaction to fire during transport and the edges properly covered. Edges
Under the Euroclass system for characterising the should also be protected against damage by lashings
reaction to fire performance of materials, the deemed or other banding, this is particularly important for soft-
to satisfy ratings shown in Table A2.34 are given in boards. All panels should be installed at a moisture
European Commission Decision 2007/348/EC. content as close as possible to that which they will attain
in service in order to minimise any movement problems.
If the manufactured product does not satisfy any of these
minimum requirements and a reaction to fire claim is to Once on site, it is preferable for individual panels to
be made in a DoP for CE marking purposes, then it must be ‘stickered’ before installation in order to allow air to
be tested and classified according to BS EN 13501-1. circulate and to allow the panels to attain a moisture
However if no claim is made in the DoP for CE marking content as close as possible to the final in-service
purposes it is still possible to use the British standard moisture content. Further guidance on storage and
system to make a separate claim. handling can be found in PanelGuide Section 4.

Further information on the reaction to fire testing in Working with fibreboards

both the BS and EN systems is provided in PanelGuide Fibreboards can be sawn, routed, spindled or drilled.
Section 2.2.3. Satisfactory results can be achieved using hand tools,

Table A2.34: Reaction to fire classification without further testing of fibreboard

Product EN Product End use condition(6) Minimum Minimum Class (7) Class (8)
standard density (kg/m3) thickness (mm) (excluding (floorings)
floorings)
Fibreboard, hard(1) BS EN 622-2 Without an air gap behind the panel 900 6 D-s2,d0 Dfl-s1
Fibreboard, hard(3) BS EN 622-2 With a closed air gap not more 900 6 D-s2,d2 -
than 22mm behind the wood-based
panel
Fibreboard, hard & BS EN 622-2 Without an air gap behind the 600 9 D-s2,d0 Dfl-s1
medium(1),(2),(5) BS EN 622-3 wood-based panel
Fibreboard, hard & BS EN 622-2 With a closed or an open air gap 600 9 D-s2,d2 -
medium (3),(5) BS EN 622-3 not more than 22mm behind the
wood-based panel
Fibreboard, BS EN 622-3 With a closed air gap behind the 600 15 D-s2,d0 Dfl-s1
medium(4),(5) wood-based panel
Fibreboard, BS EN 622-3 With an open air gap behind the 600 18 D-s2,d0 Dfl-s1
medium(4),(5) wood-based panel
Fibreboard, hard(5) BS EN 622-2 Any 900 3 E Efl
Fibreboard, medium(5) BS EN 622-3 Any 400 9 E Efl
Fibreboard, soft BS EN 622-4 Any 250 9 E Efl
(1) Mounted without an air gap directly against class A1 or A2-s1, d0 products with minimum density 10 kg/m3 or at least class D-s2, d2
products with minimum density 400 kg/m3
(2) A substrate of cellulose insulation material of at least class E may be included if mounted directly against the wood-based panel, but not
for floorings
(3) Mounted with an air gap behind. The reverse face of the cavity shall be at least class A2-s1, d0 products with minimum density 10 kg/m3
(4) Mounted with an air gap behind. The reverse face of the cavity shall be at least class D-s2, d2 products with minimum density 400 kg/m3
(5) Veneered phenol- and melamine-faced panels are included for class excl. floorings
(6) A vapour barrier with a thickness up to 0,4mm and a mass up to 200 g/m2 can be mounted in between the wood-based panel and a
substrate if there are no air gaps in between
(7) Class as provided for in Table 1 of the Annex to Decision 2000/147/EC
(8) Class as provided for in Table 2 of the Annex to Decision 2000/147/EC
NOTE: The classes given in this table are for unjointed panels, T&G jointed panels installed according to DD CEN/TS 12872 and fully
supported joints installed according to DD CEN/TS 12872

PanelGuide (V4) Annex 2F 4

but quicker and more consistent results can be achieved Surface coatings
using either portable or fixed power tools. Mediumboard and hardboard can be painted with
conventional oil-based and water-based paints, applied
When cutting wood-based panels it is important to by spray, brush or roller. Matt, satin or gloss finishes can
pay attention to normal good practice, sharp cutters, be obtained. Little preparation of the surface should be
adequate support close to saws and cutters, elimination required; dust and grease should be removed from the
of machine vibration and correct allowance for saw kerf. panel, if necessary using white spirit.

The quality of cut is dependent on the cutter type, tool Panels should have a primer or sealer coat applied, this
and material speed and also on the material type and can be proprietary hardboard sealer or a coat of emulsion
density. Tools must be kept sharp, as dull cutters will paint. Some types of oil-treated hardboard, which contain
cause edges to ‘bell’. natural or added oils, require priming with an aluminium
primer or multi-purpose primer.
Fibreboards can be drilled using all types of wood-
working drill bits. If panel edges will be visible after completion it may be
necessary to seal these with hardboard sealer or with a
Fixing fibreboards wood or cellulose filler prior to the application of finish.
Hardboards and mediumboards can be fixed with panel
pins, nails, staples, and screws; the type used will Softboard can be painted with conventional oil-based
depend upon the end use. Screws through thinner hard- and water-based paints, applied by spray, brush or roller.
boards should have cups if ‘pull through’ is a possibility. Matt or satin finishes can be obtained. Panels should be
Hardboard and mediumboard can be bonded with most brushed free of dust before decoration commences. No
types of woodworking adhesives. Fixings into hardboard rubbing down of the surface should be required.
and mediumboard should generally use cavity fittings.
Natural and ivory faced panels should have a primer or
Softboards can be fixed with nails, staples and screws; sealer coat applied, a 50/50 mix of emulsion paint and
the type used will depend upon the end use. Nails water is suitable for this purpose. White primed soft-
with large heads are recommended and screws should boards can be painted without using a sealer coat.
be fitted with cups. Softboard can be bonded with
most types of woodworking adhesive and with bitumen If further coating is applied, an alkali resisting primer is
adhesives for applications such as roofing. Due to their required and the panel or paint manufacturer’s advice
low density, softboards will not hold fixings satisfactorily should be sought.
when these are loaded. An appropriate type of cavity
fixing which will spread the load should be considered. If panel edges will be visible after completion it may be
necessary to fill these with a wood or cellulose filler prior
Finishing to the application of finish.
Fibreboard (except bitumen impregnated fibreboards)
provides a suitable substrate for paints, stains, varnishes Textured coatings can also be applied, care is needed in
and textured coverings. Lining materials such as detailing panel joints which should be either scrimmed
wallpaper, hessian and other fabrics can also be applied, and filled or featured by leaving small gaps between
providing an appropriate adhesive is used. adjacent panels.

Hardboards and mediumboards can be veneered and Coating manufacturers’ recommendations regarding
laminated with high and low pressure laminates, paper priming of panels should be closely followed. After joint
and PVC foils. treatment, the paint is applied and textured (stippled,
combed etc). The edges are normally finished by using a
Some brands of fibreboard are available pre-decorated. small brush to produce a plain margin.

Table A2.35: Fibreboards – common hazards and methods of control

Activity Hazard Control

Manual handling Large panel sizes present a risk of • Store carefully in uniform stacks on a flat level base
(in full panel form) strain or crush injuries if not handled • Use mechanical handling equipment
correctly • Adopt correct manual handling procedures
Carpentry work • Wood dust in general (including dust • Off site: preparation under exhaust ventilated plant
Activities likely to produce high dust from fibreboards) has health risks – • On site: enclosure and exhaust ventilation
levels include: it may cause dermatitis and allergic • Dust extraction on portable tools
respiratory effects • Good ventilation
• Sanding by machine and hand
• Wood dust is flammable • Respiratory protection equipment (RPE)
• Sawing, routing and turning
• Hand assembling machined or Note: Any health hazards arising from the use of fibreboard
sanded components at work can and should be controlled by compliance with
the requirements of the Control of Substances Hazardous
to Health (COSHH) Regulations 2002

PanelGuide (V4) Annex 2F 5

Further details concerning cutting, fixing and finishing
are given in PanelGuide Section 4.

Health and safety

In common with other wood products, fibreboards are
safe when they are handled and used correctly.

When cutting or machining fibreboards, wood dust is

produced and as this can be hazardous, measures must
be taken to control the dust. This is normally carried out
with the use of a suitable personal dust mask or by dust
extraction systems in a workshop environment.

Dust from cutting operations can be controlled by

complying with the Control of Substances Hazardous
to Health (COSHH) Regulations 2002. Under these
Regulations, wood dust has a Workplace Exposure Limit
(WEL) of 5 mg/m2, which is appropriate to wood dust
from the machining of fibreboards. Exposure must be
reduced as far as possible below this limit.

The formaldehyde potential of wet process fibreboards

can be considered to be extremely low and may be
considered to be within the lowest class specified in
European Standards without testing.

As with all wood-based panels, there may be handling

hazards and COSHH Regulation 6 requires an assess-
ment to be made, and recorded of health risks associated
with wood dust and handling. Common risks and control
measures are shown in Table A2.35.

References
1 B
 S EN 622-1. Fibreboards. Specifications. General
requirements, BSI
2 B
 S EN 622-2. Fibreboards. Specifications.
Requirements for hardboards, BSI
3 B
 S EN 622-3. Fibreboards. Specifications.
Requirements for medium boards, BSI
4 B
 S EN 622-4 Fibreboards. Specifications. Requirements
for softboards, BSI

PanelGuide (V4) Annex 2F 6

PanelGuide Version 4
ISBN 978-1-909594-21-0

Published in 2014 by the Wood Panel Industries Federation, TRADA Technology Ltd (a BM TRADA
company), and the National Panel Products Division (a division of the Timber Trades Federation)

Previous editions are listed in Annex 4 of the PanelGuide

This is a technical book for professionals in the built environment sector. While every effort is made to
ensure the accuracy of the advice given, the project partners cannot accept liability for loss or damage
however caused arising from the use of the information supplied

All rights reserved. PanelGuide may be downloaded and printed for single use only. You must request
the permission of the copyright owners if you wish to extract content from the PanelGuide or use it for
any other purpose

© Wood Panel Industries Federation, TRADA Technology Ltd (a BM TRADA company), and the
National Panel Products Division (a division of the Timber Trades Federation)

Unless otherwise stated in the caption, all photographs and illustrations included in the Panel Guide
are © Wood Panel Industries Federation, TRADA Technology Ltd and the National Panel Products
Division

Revisions to PanelGuide Version 4 contributed by Ian Rochester (WPIF), Vic Kearley (BM TRADA)
and Nick Boulton (TTF)

Produced by the publishing team at BM TRADA, the official publisher for the Timber Research and
Development Association

Contact details for the PanelGuide project partners are:

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PANEL
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PanelGuide (V4) 1