Masonite Underlay
Masonite™ Underlay is for use over strip timber,
particleboard and plywood floors to provide a flat,
uniform, indent resistant base for resilient sheet
and tile floor coverings including flexible and semirigid PVC, cork, rubber, linoleum and cushioned
vinyl.lt may also be used beneath textile floor
coverings.
The application of Masonite Underlay offers
particular benefits in that it:
1. Is suitable for use in residential, commercial
and institutional buildings;
2. Bridges small irregularities and joins between
s u b f l o o r t i m b e r s or wood-based sheet
materials.
3. Is tough, flexible and resistant to cracking or
fracturing;
4. Minimises the adverse effect of subfloor
dimensional movement on the floor covering;
5. Adds strength and stiffness to the subfloor;
6. Provides a smooth, fine surface for the uniform
and economical application of adhesive;
7. Lessens the residual indentation of resilient
floor coverings which can occur when the
coverings are applied over soft underlays and
substrates e.g. softwood, plywood, paper felt;
8. Is easy to work and fix with normal carpenter
tools and flooring installation equipment.
Special tools are not necessary;
9. Will not split or f r a c t u r e during normal
working and fixing;
10. Is a light weight, easy-to-handle wood panel
product;
11. Improves the life of resilient floor coverings;
and
12. Is recommended by all leading manufacturers
of resilient floor coverings.
Relevant Australian Standards
The following Australian Standards refer to the
installation of floor coverings and hardboard
underlay:
•
•
AS 1884-1985: Floor Coverings-Resilient Sheet
and Tiles - Laying and Maintenance Practices.
AS/NZS 2455.1-1995: Textile Floor Coverings Installation Practice.
The Product
Masonite Underlay is a 5.5mm thick, reduced
density hardboard. It is manufactured to comply
with the requirements for Standard Hardboard -
Type R.D. in Australian Standard 2458-1982,
Hardboard.
The material is accurately dimensioned and a close
thickness tolerance of ±0.15mm is achieved by
sanding the back surface.The face surface is
smooth.
Product Details
Dimensions:
Tolerances
(ex mill)
Squareness:
Area:
Mass per unit
area (weight):
Packaging:
Bundle details:
1220mm x 915mm x 5.5mm
Length
± 1.0mm
Width
±1.0mm
Thickness
± 0.15mm
Variation in diagonals not
more than 1.0mm
1.12m2 per sheet
Approximately 5.3kg/m2
or 5.9kg per sheet.
Bundles of eight sheets, paper
wrapped.
Bulk pack, (120 sheets) strapped
to a disposable timber pallet.
Coverage:
8.9m2
Mass:
47kg
Dimensions:
1220mm x 915mm x45mm
Properties
The following table is based on data from
production and research centres. It is intended as a
guide to the properties of Masonite Underlay. If
more accurate information is required on these or
any other properties please contact your Australian
Hardboards sales office.
Property
Unit
Typical
Value
Density
kq/m3
2
960
Mass/Unit area
kg/m
5.3
Modulus of Rupture
MPa
30
Modulus of Elasticity
MPa
4000
Impact Strength
J/m2
4000
Internal Bond Strength
kPa
1000
Thermal Conductivity
W/(m.K)
0.18
Hygro-expansivity
%
0.25
(change in face dimensions over 50% to 90%
relative humidity)
Handling and Storage
Sheet Layout
Keep clear of sharp protrusions. Stack panels flat
on pallets or timber runners in a dry area with a
moderate temperature and reasonably constant
relative humidity.
Remove the Masonite Underlay sheets from the
bundle and lay them, smooth face upwards on the
floor surface. (See also "Site Conditions.")
Storage in direct sunlight, damp locations or hot,
dry buildings should be avoided.
Subfloor
Suitable subfloors for the application of Masonite
Underlay include:
1. New or old structural timber floors.
2. Structural Plywood Flooring.
3. Structural Particleboard Flooring.
Installation
Preparation
Before installing Masonite Underlay, check that the
ventilation to the subfloor area is adequate and
provides a clear cross flow of air beneath the floor.
The subfloor area should be free of excess
moisture vapour and dampness. (Refer "Site
Conditions.") The subfloor timbers and flooring
must be in reasonable condition, dry and free from
decay.
Arrange the sheets in the rows in an ashlar or
brickwork pattern. Keep the long edges at right
angles to the run of the flooring. Allow a 3mm
gap between the sheet edges and room perimeter.
Also where the sheets meet other fixtures.
Bring adjoining sheets almost into contact with
one another. Do not force them together. The
preferred gap between sheets is 0.4mm. The sheet
joins should be located over the centre of
floorboards.
Cutting
Masonite Underlay can be cut and worked with
normal carpenter tools. Cut sheets with a fine
tooth hand or power saw.
P r o f e s s i o n a l floor layers may prefer to cut
Masonite Underlay with a linoleum or Stanley
knife. Always keep the cut edges to the room
perimeter.
Replace any loose or broken boards. Floor nails
should be punched below the floorboard surface.
Masonite Underlay is sufficiently rigid to bridge
minor irregularities in the floor surface. The best
results are obtained when the floor is machine
sanded to a flat plane.
A convenient way to mark and cut Masonite Underlay to fit
up to walls is to slide the sheet under the unfixed edges of
the previous sheet as shown.
Fixing
Staples or nails are recommended to fix Masonite
Underlay to strip timber subfloors.
Location of joins over typical strip timber and sheet flooring.
On structural particleboard and plywood sheet
flooring it is advisable to use staples or nails in
conjunction with adhesive.
Staples
Use 22mm minimum length galvanised or
copper etched narrow crown type, preferably
resin coated.
The recommended nails will give better hold
than staples and are preferred for softwood
floors, such as Pinus Radiata and Baltic Pine.
Fastener Spacings
The correct spacings for staples and nails into
strip timber floors are 75mm at the sheet
edges, 10mm from the edge and 150mm
throughout the body of the board. Ensure that
the fasteners are not driven into the floorboard
joins.
Adhesives
Use adhesive with staples or nails when fixing
Masonite Underlay to structural sheet flooring.
Adjust the staple gun to set the staple crown
0.4mm maximum below the Masonite
Underlay surface.
Suitable adhesives include neoprene type wallboard or construction grade adhesives such as
H.B. Fullers "Maxbond".
Staples must not be driven deeply into the
board.
Some high solids, flexible PVA adhesives may
also be used. Please obtain advice from the
adhesive manufacturer.
Nails
Apply the adhesive to structural sheet flooring
in a grid pattern approximately 150mm apart
in both directions. Wallboard type adhesives
are usually applied by sealant gun in
continuous beads a p p r o x i m a t e l y 5mm
diameter.
Use 25mm x 2mm x 3.5mm head, ring grooved
buttress type underlay nails.
PVA type adhesive may be applied with a fine
"V" notched spreader, 1.5mm x 1.5mm
maximum. Only apply sufficient adhesive to fix
one sheet at a time.
Drive nails flush with or slightly below the
Masonite Underlay surface.
Laying procedure and fastenings
PART PLAN
Position the Masonite Underlay and fasten with
nails or staples spaced at 150mm centres at
sheet edges and throughout the board.
Adhesives should be applied in accordance
with the manufacturers instructions. Do not
use adhesive when fixing Masonite Underlay to
strip timber floors.
Fastener Spacings
Finishing
Check to ensure that all fasteners are correctly
driven and that fasteners heads are not proud
of the board surface.
Carefully sand the Masonite Underlay joins to a
flat plane. Also sand the fixing points to
remove any fibre build-up.
When sanding, use a flat based machine
sander or sandpaper block. Do not use small
disc type sanders.
Sweep or vacuum the floor so that all dust and
loose fibre is removed. The Masonite Underlay
is then ready to receive the floor covering
material.
Floor Coverings
The floor covering manufacturer's instructions
should be followed in relation to the selection
and use of adhesive and for the installation of
the floor covering material.
Where required, the Masonite Underlay surface
may be sealed to suite some adhesive systems.
Use shellac/methylated spirits solution or
proprietary sealers in accordance with the
adhesive manufacturer's instructions.
Semi-rigid vinyl tiles should be bonded with an
adhesive which remains permanently tacky,
such as "Staybond 7102" Vinyl Flooring
Adhesive, manufactured by International
Adhesives and Resins Pty Ltd.
The cause of moisture must be corrected and
the floor allowed to dry.
Subfloor ventilators should provide a clear,
cross flow of air beneath the floor so that any
excessive moisture vapour is removed from the
subfloor area. Excess moisture and dampness
can lead to the distortion and possible decay of
flooring members and excessive movement of
the Masonite Underlay.
Adequate ventilation is particularly important
where impervious floor coverings are used, as
they restrict the escape of moisture through
the floor.
In some circumstances, a moisture impervious
membrane, such as polyethylene film or
bitumen impregnated felt, may be used to
cover the ground beneath the floor to retard
moisture rise.
Further information on subfloor ventilation is
contained in the Forestry Commission of NSW
Technical Publication No. 11 - "Ventilation
Under Timber Floors." Copies are available
from your Australian Hardboards sales office.
Under normal climatic conditions, Masonite
Underlay may be used direct from the bundle,
however, best results will be achieved when
the Masonite Underlay is loose laid on the floor
for 24 hours before fixing. This will allow the
material to equilibrate its moisture content
with the site conditions.
The practice of loose laying the board for 24
hours is strongly recommended where there is
any doubt on the adequacy of the subfloor
ventilation.
Site Conditions
Note
Prevailing climatic or installed environmental
conditions can influence moisture content
changes in wooden floors and underlays. The
resulting dimensional movement may become
noticeable where the floor covering bridges the
Masonite Underlay joins.
In some cases, the joins may be highlighted by
the effects of glancing light on the floor
surface.
Masonite Underlay should only be installed
over floors which are adequately ventilated and
where there are no indications of dampness.