Tag Archives: Decking

Reducing rot in wooden sun decks

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preventing rot in wooden decks

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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.

preventing rot in wooden decks

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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.

For a free, no obligation quote or for some advice please feel free to contact us on 082 496 5444 or complete the form below and I will contact you. Please also feel free to leave comments below.

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Wooden Sundeck Constructed in Toti Durban

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This wooden sundeck we constructed in Durban was a low-level deck which was barely off ground level. We were taking it flush off the level of the floor in the lounge and extending it outwards into the garden. The grass was not growing properly in this area due to large trees that were creating a large shadow so the client wanted to deck it to eliminate this problem.

The biggest challenge when building a wooden deck near or on ground level is to get a support beam underneath the joists where needed. There are two methods one can use. The first is what I call the cleat and beam system whereby a beam is placed underneath the joists to give them their support. We normally use a 38 x 114 joist and a 50 x 228 beam. One needs to span the 38 x 114 to a maximum of 2m but 1.8 is preferable. So every 1.8m to 2m one needs to slot an under beam below so as to support those joists. Posts should be used every 3m on the 50 x 228 beam. With this spec one can save on timber while still providing adequate support so that the deck is structurally sound.

The problem with this system arises because if you have a 228 beam, plus a 114 joist and then a 19mm deckboard on top of that your total height needed above ground level is 361mm. If the deck is too close to ground it will mean excavating soil to be able to drop that beam down enough to still arrive at the original height of your deck. Although this is quite possible and not that too time consuming, it sometimes results in the main beam sitting in soil or it may come into contact with wet soil over time. One must therefore use at least H4 CCA Treated SA Pine as the beam and in fact that whole substructure should be H4, even though the joists aren’t in contact with soil, to ensure that no rot will occur.

The other method is to create a frame, all in the same plane using 38 x 114 and use no under beam. This will result in the deck only being 133mm in height so that no excavation will be needed in order to bring the deck up to the required height. However now that you don’t have a beam to attach posts to, you will need to attach the posts to the joists and fascia beams. Again this is not a problem, but it will require a few more posts than in the first method as you can only span your 38 x 114 to a max of 2m. Hence more posts, more concrete and more labour in digging holes.

We used the joist and beam system here as we had enough space below to set the beam without having to dig too far into wet soil. So our work was made lighter by not having to dig too many holes.

Once the substructure is up, the deckboards can go down. On this wooden deck we used 19 x 68 balau deckboards. We used two deckboards as a fascia to cover our joists and beams, filled our holes with epoxy, sanded and sealed.

For a free no obligation quote or advice on your deck or other outdoor timber construction please call us on 082 496 5444 or use the form below to contact me.

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