Storage and Handling
Hardwood decking should be kept dry and out of the weather until installation. On site each pack
should be kept off the ground by placing it on bearers and covered to protect from sun and rain.
Free air circulation under the decking is very important to help minimise cupping and warping.
Proper ventilation ensures the potential difference in moisture levels between top face and the
underside of the boards is reduced and extends the life and performance of the deck.
The sub deck should have at least 450mm clearance from the ground. This, in conjunction with
suitable spacing, will allow for adequate ventilation. NB: It is important that the perimeter of the
deck is not fully enclosed by a surround, and remains open to airflow. Completely enclosing the
sides of the deck will inhibit proper ventilation and compromise the performance of the decking.
In wet areas or over water, additional clearance is recommended. Failure to provide for suitable
ventilation is a major cause of early decking failure.
Other steps that can be taken to minimise moisture differential are:
1. A ground level vapour barrier (with slit drainage).
2. A suitable surface coating on all four sides of the decking boards (refer coating section).
Decking 19mm thick should be installed at maximum 450mm joist centres. For 32mm thick
decking this can be increased up to 600mm joist centres.
End sealing will help minimise splitting and checking at the ends of the boards. We recommend
the boards be end-sealed with a quality penetrating oil as soon as possible after cutting and
before final installation.
Cleaning & Washing
Hardwood decks should be cleaned with a stiff brush at least once a year to clear gaps and
remove surface mould which can be a slip hazard in wet weather. It is also important for the life
of the deck to keep it clear of leaf litter, moving pot plants or other large objects that may hold
moisture to the top of the deck.
Hardwood decking can be waterblasted BUT it is important to do so at a low pressure so as not
to damage the fibres of the board by going too hard and/or too close. Care must be taken not to
stop at the end of the stroke but to lift the nozzle away when changing direction.
Washing/brushing the deck down with a mild solution of janola and water (1:16), or suitable
equivalent, will remove any build up of resin or extractives that may leach out of the timber as the
pieces “season” in situ. There are also various chemical cleaning agents available, from
detergents through to acids. Follow manufacturer’s instructions and be conscious of the run off.
Kwila has quite considerable reserves of extractive and readily stains all adjacent materials. It can
only be removed with chemical stain removal products, such as Timber Wash
www.homesafeproducts.co.nz. The amount of run off will depend on the specie, how dry it is
before the decking is laid and how long exposed the deck is to the weather.
Woodmart’s Hardwood Decking is manufactured with care and inspected to ensure quality, but it is a
natural wood product and subject to variations in weight, density, colour, grain and performance.
Care must be taken at installation and maintenance to allow for movement.
Some swelling, shrinkage, movement and checking are normal occurrences in timber decking.
NB: At this time, Woodmart does not endorse the use of hidden fixing systems with this
1.1 Intended Use
These Hardwood Decking Instructions are designed as a guide for the correct installation of Woodmart Ltd. hardwood decking species.
The Woodmart hardwood decking shall be installed over a substrate constructed in accordance with NZ Standard 3604(2011).
2. Health and Safety
2.1 Cutting of Timber
Cutting of timber is to be done in a well ventilated area and a suitable dust mask, eye and ear protection must be worn.
Woodmart recommends that all deck timber species should be envelope coated before installation, including all cut ends and areas of exposed fresh timber.
Avoid coating the top surface only, once installed, as this will likely cause movement (cupping) in the timber surface.
Coating or priming is to be done in a well ventilated area, refer to the coating/primer manufacturers requirements for all matters relating to health and safety. Ensure all of the coating manufacturer’s requirements are be adhered to.
3. Site Preparation
3.1 Structure and Framing
3.1.1 New Zealand Standard 3604
Generally, the timber substrate and framing must comply with NZS 3604 (2011) (Timber-framed buildings), however where specific engineering design is required the framing shall be at least of equivalent stiffness as the framing provisions of NZS 3604.
Joists or bearers must be at a spaced at a maximum of 450mm centres, (for ex 25mm thick profiles) and maximum 600mm centres (for ex 50mm thick profiles).
6. Fixing Details for decking
6.1.1 Fixing Method
Align profiles perpendicular to joists. Pre-drill all fixing holes, using a drill bit that is slightly smaller than the screw or nail shank, to reduce the risk of splitting and ensure a snug fit.
Fixing placement for a 90mm wide board to be 12.5mm in from each edge of profile, and for a 135mm, or wider, board, 15mm in from each edge of profile.
Woodmart Ltd recommends using stainless steel, countersunk twin thread decking screws for all decking profiles. Fixings must be long enough to achieve a minimum 40mm framing penetration.
6.1.2 Board Spacing
Allow a gap between boards to ensure free draining during wet periods.
As a general guide a gap of 3 – 8mm should be allowed for between boards, but the size of gap will need to be determined by species, board width, site, location and coating.