| Perhaps the most important consideration in | | | | including Teak, Jarrah, Jatoba, Bongossi, |
| choosing the lumber species to use for | | | | Purpleheart, Selangan batu, Western Red |
| exterior decking is the durability | | | | Cedar, Merbau, Blackbutt, Spotted Gum, River |
| characteristics of the lumber to be used. | | | | Red Gum etc. |
| Unfortunately this is not a precise science | | | | |
| as wood is a natural species, with | | | | The third group, Class 3 is termed |
| significant variations even within the same | | | | "Moderately Durable". Such species will give |
| species. For example a species grown in one | | | | good service without preservative treatment |
| country may have significantly different | | | | if clear of the ground and used in conditions |
| durability characteristics to the same | | | | of low termite hazard and involving only |
| species grown in another country. This may be | | | | intermittent wetting followed by reasonably |
| due to more rapid growth, harvesting at an | | | | rapid drying. Such timbers can still be used |
| earlier age or to a lesser extent, | | | | for exterior decks but it would probably not |
| differences in processing. Furthermore, | | | | be advisable to use such species in severe |
| similar species may have sub-species which | | | | weather conditions unless a maintenance |
| could exhibit totally different durability | | | | regime involving the application of good |
| characteristics. | | | | quality decking oil is carried out at regular |
| | | | intervals. Species in this group include |
| Due care should be taken that any wood does | | | | Cambara, Kempas, Karri, Eucalyptus saligna. |
| not contain the outside sapwood. Sapwood of | | | | |
| most hardwood species is non durable and will | | | | The final group Class 4 is termed "Non |
| decay quite rapidly even if the heartwood | | | | Durable". Timber species in this group are |
| itself is rated as highly durable. With some | | | | considered unsuitable for exposed decking |
| cypress species in particular, the sapwood is | | | | because of their low natural durability. |
| prone to decay extremely quickly. Fortunately | | | | |
| sapwood is generally a lighter color, so can | | | | But apart from resistance to the ravages of |
| be reasonably easily distinguished. | | | | sunlight, rainfall and humidity, in many |
| | | | locations there is another factor to consider |
| To a large extent, the denser, harder lumber | | | | - termites. There is no direct correlation |
| species generally possess higher durability | | | | between durability and resistance to termite |
| properties. These are often referred to as | | | | attack so care needs to be taken in termite |
| Class 1 or "Highly durable". Examples of such | | | | prone areas. Suitable species with high |
| species includes Ipe, Cumaru, Tallowwood and | | | | resistance to termite attack would include |
| Ironbark. Under normal conditions, not in | | | | Ipe, Cumaru, Jatoba, Teak, Jarrah, Selangan |
| permanent contact with water, such species | | | | batu etc. |
| can be expected to resist decay and insect | | | | |
| attack for at least 25 years and up to 50 | | | | Finally and perhaps of lesser importance is |
| years. | | | | that the lumber chosen should not twist, cup |
| | | | or deform in service. This requires some |
| The next group is Class 2 where the lumber | | | | skill and experience on the part of the |
| species are termed "Durable". Lumber species | | | | lumber mill as the majority of hardwoods |
| included in this group also exhibit | | | | require carefully controlled kiln drying to |
| exceptional durability characteristics and | | | | bring the moisture content of the wood down |
| the wood can typically be expected to have | | | | from more than 25% with freshly cut timber to |
| life of 15 to 25 years or more. Some species | | | | approximately 16%. If the timber is dried to |
| in this group closely approach the | | | | fast it can crack and twist when in service. |
| performance of the Class 1 timbers even under | | | | Even when properly kiln dried, all timber |
| severe conditions of service and in fact all | | | | will expand and contract to some extent in |
| species in this group may be regarded as | | | | service particularly in damp conditions. In |
| approximating the service of Class 1 timbers | | | | such conditions, a timber species with a low |
| where conditions are less severe, as in | | | | shrinkage rate may be preferable. Such |
| typical decking. | | | | species would include Ipe, Selangan batu, |
| | | | Merbau and Teak amongst others. |
| This group includes a large range of species | | | | |