One of the more important factors to consider when choosing a wood deck tile is the lumber species to use, as characteristics such as durability and wearability can vary quite significantly between different wood species. With durability however it’s unfortunately not a precise science as durability can vary quite significantly within the same species. In particular, certain species may be natural harvested or others may be plantation grown and harvested at a much younger age.
It’s also important to ensure that any wood chosen does not contain any sapwood, or no more than about 10%. The reason is that sapwood of most hard wood species is non-durable and therefore can decay particularly rapidly even though the heartwood may be classified as highly durable. Fortunately, sapwood can be fairly easily distinguished in most cases because it tends to be a much lighter color than the heartwood
Wood species are typically graded into one of four durability categories:
Highly durable – Class 1
Generally speaking, the denser, harder lumber species will possess the highest durability. Such species are referred to as Class 1 or “Highly durable”. Examples of such species includes Ipe, Cumaru, Tallowwood and Ironbark. Under normal conditions, and not in permanent contact with water, wood of such species can be expected to resist decay and insect attack for at least 25 years and up to 50 years in many cases. Archarak’s structural wood tile range includes Ipe wood.
Durable – Class 2
Lumber species in the “Durable” group also exhibit outstanding durability characteristics with the wood typically having a life of 15 to 25 years or more. Some species in this group closely approach the performance of the Class 1 timbers even under severe conditions of service. In fact all species in this group may be regarded as approximating the service of Class 1 species where conditions are less severe, as in typical decking.
This group includes a large range of species including Teak, Jarrah, Jatoba, Bongossi, Purpleheart, Selangan batu, Western Red Cedar, Merbau, Blackbutt, Spotted Gum, River Red Gum.
Moderately durable – Class 3
Species in the “Moderately Durable” group can be expected to provide good service life without preservative treatment if the wood is kept clear of the ground with only intermittent wetting followed by reasonably rapid drying. Such species could still be used for exterior decking purposes but it would not normally be advisable to use such species wet weather conditions are more severe unless a strict maintenance schedule of coating the deck with a good quality decking oil is followed.
Some species in this group include Cambara, Kempas, Karri, Eucalyptus saligna.
Non Durable – Class 4
Lumber species in the “Non Durable” group should not be used on decking fully exposed to the weather because of their low natural durability.
Apart from decay due to weather conditions, in many locations the other factor to consider this insect resistance and in particular termites. Unfortunately there is no direct correlation between durability and resistance to insect attack so both decay resistance and insect resistance needs to be taken into account in termite prone areas. Some species with high resistance to termite attack include Ipe, Cumaru, Jatoba, Teak, Jarrah, Selangan batu etc.
Twisting, cupping and bowing
Although not directly related to durability, another important factor to consider when choosing the wood species is that it should not twist, cup or deform in service. Provided the planks are nailed or screwed securely to the bearers, none of these factors should be a concern, but in the case of interlocking decking tiles it is a much more important issue as there is nothing to prevent the wood from moving in service, and some wood species are more prone to twisting than others. Although not a definitive measurement, looking at the ratio between the tangential and radial shrinkage can give some indication of stability.
Even when properly kiln dried, all timber will expand and contract to some extent particularly in humid or very dry conditions. In such conditions, a timber species with a low shrinkage rate would be preferable. Such species would include Ipe, Selangan batu, Merbau and Teak amongst others.