Decking Installation Guidelines for Class 1 Hardwoods
CLASS 1 HARDWOODS
Class 1 durability timber is the highest level of natural durability a species of wood can have. In above-ground settings, it is expected to last more than 40 years, and in-ground it has an average life expectancy of more than 25 years.
Use traditional fixing and fastening methods only. The screw should have a big head and securely hold the deck board onto the substructure. The hole in the deck board needs to be slightly larger than the outer thread diameter of the fastening being used so that the head of the fastening can properly pull and hold the board onto the substructure.
The use of modern, “sales pitch – visually enhancing” fixing systems are not suitable for class one heavy hardwoods as the stresses in the timber are simply too strong. We do not recommend the use of small headed screws, secret fixing, side fixing, deck clips, nails and/or double thread screws – only use stainless steel or nonferrous fixings and fastenings.
There are a number of reasons for this:
- Initially, tannins present in hardwoods can react with any steel it is exposed to and cause black marks to form on the wood. The tannins will ultimately be washed out of the timber depending on how much rain the timber is exposed to. Tannins occur naturally in a few hardwoods with some pieces of timber having more tannins and other less.
- Over time the anti-corrosive layer on any ferrous fastening will fail/wear out and then rust streaks will start to form on the timber
- Finally ferrous fastenings (especially the screw) will fail because of corrosion. Considering the lifespan of the class one hardwood decking, it does not make sense to have the boards coming loose because of corroded screws.
- Screw length should be at least 2 times the thickness of the deck board being used. Two screws per board across the face on every joist up to 90mm wide deck boards and three screws across the face on every joist for 140mm wide deck boards. Counter sink the top of the screw head flush with the top of the board. If the screw head is countersunk too deep, a small pool of water will accumulate every time it rains, which swells the wood around the screw and ultimately leads to screws loosening over time with constant swell – shrink movement.
Recommended joist spacing for 19mm thick boards is 400mm to 450mm max and for 30mm thick deck boards the spacing should be between 500mm to 600mm max apart. Measurements are center of bearer to center of bearer.
To get the best value from the class one deck board, a hardwood sub structure is recommended. The structure will outlast the deck board. The lifespan of the deck board is highly dependent on the conditions the deck is exposed to, but either way a long time.
Finally, a class one hardwood deck should give you many years of trouble-free service if installed correctly.
It is recommended to give the timber a light oil (Powafix TEAKOIL or similar) coating, all around including end grain, pre installation. This should weather away over a few months. The oil coating is inexpensive and very easy to apply, the coating allows for the timber to gently settle into its new environment as the humidity in the timber equalizes with its surroundings.
We do not recommend linseed oil as it is simply too thick, causes staining and remains sticky after application, (even if thinned), which attracts dirt.
Should it be your intention to varnish the timber then only an oil-based varnish or sealer should be applied. An indication the product is oil based, is when instructions for brush cleaning specify turpentine to be used.
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