I’ve often been asked to quote, on or at least comment on, composite decking. Firstly we need to have a look at what composite deck boards are.

Composite deck boards are generally made from plastic and saw dust which can be anything from saw dust, wood chips to wood fibre pieces or bamboo. They can be either be new or recycled materials. One method of manufacturing composite deck boards is by extrusion. That is the materials are mixed together and forced through an opening to create a relatively consistent size and shape. Compression moulding is the other method used and consists of taking the combined liquid materials and compressing them under high pressure and heat into a mould to create the deck board.

Composite boards cannot be used as structural material as they do not have the required structural properties of, for instance, S5 SABS approved structural or industrial grade treated pine, or balau for that matter. As such the substructure of a deck still needs to be built using H3 CCA Treated pine. If the argument is that composite decks will last longer than solid timber, then half that argument is invalid because the structure is not made from composite materials. It is only the deck boards that are from composite materials and cannot “rot” in the traditional sense. However composites can fail if the process they underwent was not sound. There are various failures that can occur. A search on Google for “composite fails” will return many ways these boards can fail from a sub standard manufacturing process to fading in extreme direct sunlight, to warping, cupping or twisting due to heat from the harsh African sun.

Sustainability and “eco friendly” is often used as an argument in favour of composites. The balau and pine we use in decks is from sustainable forestry and is certified as such when imported or harvested locally. Producing composites also requires a lot of heat which is obtained from which source? So although composites can be made from recycled materials, one also needs to factor in the carbon foot print of making them, even though it is probably less than the carbon foot print of harvesting solid timber. Composites therefore do not carry a zero carbon foot print.

From a cost point of view composites are generally more expensive than balau. As with anything, you can get cheap or expensive and the risks of buying cheap composites speaks for itself. Some composites can be up to 4 times the price per square metre of balau. A cheap composite will tend to fail quicker as opposed to a more expensive one. If the cost of these boards is up to 4 times the price of balau then it stands to reason that  ALL the balau can be replaced up to 4 times before the cost becomes the same. It is highly unlikely that you will need to replace your deck surface four times in the life of the deck. What will commonly occur in a balau deck surface is that some boards will fail before others. Any failure of balau deck boards is normally long-term in any event. Deck boards are relatively easy to replace and relatively inexpensive. It is the structure that is expensive to replace and normally results in the whole deck having to be replaced. If our structures are both CCA treated pine in both types of deck, then the greater risk lies in the structure, not the boards.

The fixing system generally used to fix these boards to the pine substructure is a hidden screw of sorts and again there are various products available each one with it’s own advantages and disadvantages. A plastic clip is often used which is slotted into a groove routed along the edge of the board and then fixed to the bearer. Two boards often share a single clip which is then concealed below the deck board. So no screw holes through the face of the board. With the screw head being so small they can fail in that the screw can be screwed too far through the plastic clip. The clip itself is plastic and at certain temperatures will fail. The clip can only be guaranteed against failure below certain temperatures. In my opinion nothing replaces a Kalgard coated decking screw counter sunk through the face of a solid timber board to limit failure. In a balau deck, screw holes are filled with a clear epoxy and saw dust mixture so are not as visible as one would think once filled and sanded flat.

Scratches and fading in composites should be taken into account. A lot of manufacturers of composites guarantee a maximum percentage fade rate. How does one measure 10% fade? If a composite deck fades or gets scratched it can’t be sanded to remove these.

Maintenance of the deck is often used as an argument for using composites over balau. Water is largely drawn into wood through the end grain and not the face or side grain. Being balau it is naturally resistant to water ingression. If you take a 20 year old piece of good quality yellow balau and cross-cut it, you will most often find that no water has been absorbed through the board. Balau deck boards can be left un-oiled which will result in a grey appearance. Oiling or not oiling a deck won’t increase or decrease the life span of the deck by any material length of time. If oiled, maintenance is simple. Oil can be sprayed, brushed, wiped, sponged or even dipped. And oil won’t peel and flake. Coatings will. So it is quick and easy to maintain. If left un-oiled a pressure clean every 6 to 12 months is sufficient to keep your deck looking good.

Based on the above I am more concerned about the structure of a deck than the surface one uses. Structures are costly to replace. Deck boards are not. The above arguments for composites do not, in my opinion, warrant using them as opposed to balau.

We will however install a composite deck for you if you so wish, but I am not convinced that you will achieve the desired result by switching from solid timber to composites.

For a quote on your deck and other timber related structure please contact us using the contact us form below or call us on 082 496 5444.