This article will focus solely on reducing rot in wooden sun decks rather than a specific article on a job we have completed.
One of the first questions that are asked when planning to build a wooden deck is that of maintenance. Being wood, the deck will always be susceptible to rot and insect infestation, but with the proper care this can be reduced to the absolute minimum and can compare favourably, if not better, to using other materials such as composites, concrete and tiles. Let’s face it when it comes to aesthetics and warmth wood is best, but often people opt for other materials simply because there is a belief that they are easier to maintain and will cost less in the long run.
Rot is caused by a break down in the fibres of the wood. A breakdown in the fibres of the wood is caused by algae being allowed to grow on the timber which in turn is caused by water. Water therefore does not directly cause rot. A piece of wood can live in water all its life and not rot, but if it is not cared for properly then it will cause algae to grow and ultimately rot. CCA Treated timber of course eliminates this because it contains copper which prevents algae from growing. However it is only possible to CCA treat certain timbers such as pine and to a degree Saligna because of the differing densities of the woods. Pine is soft and balau is hard. CCA treatment is done through pressure treating (vacuum) and it is therefore impossible to CCA treat balau as it is too hard for the solution to penetrate the timber.
So how does one reduce the chances of balau rotting? Well first of all balau is naturally resistant to rot because it is twice as dense and twice as hard as pine for instance so the water doesn’t penetrate it as easily. Also it contains natural oils and resins which repel water. So it will rot, but it will take longer than other timbers.
A piece of wood, any wood, takes in water largely through the end grain. Very little water is absorbed through the face or side grain. Think of it as a bunch of straws. When the straws get wet on the ends they can take up water, but they can’t take up water through the sides.
So the important areas of your deckboard is of course the ends, or end grain. Where a deck board is cut, there is not much that can be done to stop water ingression except to seal it with a suitable water-repellent sealer after or during installation. When a deckboard comes from the timber yard it is often closed off on the ends with wax. However that board needs to be cut in order to fit into the deck so one end will always be wax free. Also it is not advisable to leave that wax on. In the hot sun the wax starts to melt and leaves unsightly marks on the joins. So it is best to cut the wax off before installation. That leaves two ends exposed which now need to be sealed off as best as possible using sealer. Apply it liberally to the ends and make sure they are re-sealed during maintenance intervals.
The other area that is vulnerable is where the screw hole is drilled through the deckboard to attach to the joist. This leaves a hole where water can penetrate the end grain on two sides. What compounds this problem is that the screw is normally counter sunk which allows water to collect in the hole and be absorbed up and down the end grain. Some deck builders use a stop bit to insert the screw whereby the screw head stops at the surface of the deck. I don’t however use this method for two reasons. Firstly the screw is now not tight up against the bottom of the counter sunk hole so the board may work itself loose over the years. Secondly, there is still a small gap around the screw head for water to get into and move along the end grain. And trust me water will find that hole. You will often see deckboards that have started rotting at the screw holes. Now you know why.
Instead I counter sink the screw hole about 5mm, insert the screw and tighten it until it is tight right up against the bottom of the hole leaving the screw head counter sunk a few millimetres. I then take a clear epoxy, mixed with the sawdust of the same timber to match the colour, and force it into the hole leaving it slightly proud. Try and use a very fine saw dust. It makes mixing the epoxy much easier and it goes in the hole better. Once it is dry, I use a grinder with sanding pad to flat it and then I use a rotex sander to remove the scratch marks left by the grinder. Now it is ready to be sealed and good luck to any water that thinks it can get in there. The epoxy is the only filler that will last. Wood filler will pop out in a few months’ time. Use a clear epoxy as the saw dust will match the colour of the deck. White or grey epoxy will leave a white or grey mark on the surface.
It takes more effort and takes longer to do it this way, but my crew has it done to a T now. And the net effect is a better built deck that will last longer and will cost less to maintain. So there you have it, the warmth of wood without the hassle and without having to settle for alternative materials.
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