Timber iQ April - May 2019 // Issue: 43 | Page 36

FEATURES Balau was the timber choice for a beach house in Bakoven, Cape Town. regularly discuss these options with architects, installers and their clients to ensure that any selection is appropriate. Treated South African pine is also a commonly used softwood option for outdoors, but its characteristic green stain means that it has limited aesthetic appeal for prestigious residential and commercial developments. HARDWOODS Many tropical hardwoods like Balau (Shorea spp.), garapa (Apuleia leiocarpa), purpleheart (Peltogyne spp.) and iroko (Milicia excelsa) are well suited to cladding applications and are regularly used. These hardwoods will typically be knot-free and are rated in Durability Class 1 or 2. Generally they are also harder and stronger than softwoods, but their additional weight is an important consideration. They are too dense to be treated with preservative and are also usually left uncoated. A surface treatment can be applied if desired, to slow the natural weathering process, but unfinished is usually preferable due to the low maintenance requirement. Temperate hardwoods like European oak (Quercus robur) and sweet chestnut (Castanea sativa) are commonly used in Europe, but have not historically been used in South Africa. MODIFIED TIMBERS Over the past decade or so, we have seen the rise of a number of modified timber options – either thermal treatment or chemical modification. These processes typically result in greater dimensional stability and significant improvements in durability of otherwise non- durable species. 34 APRIL / MAY 2019 // One of the key areas of focus when selecting or specifying timber cladding is its durability. Thermally modified species available in South Africa include oak, yellow poplar and pine. Pricing is dependent on species, but is not dissimilar to tropical hardwood. The thermal modification process involves the heating of timber which burns off many of the sugars which would otherwise support fungal infection or encourage insects. It also darkens the timber to a rich brown, which fades as the timber weathers. Special mention should also be made to the traditional timber treatment technique known as Shou Sugi Ban. This ancient Japanese method of charring the outer surface of cladding boards significantly improves the durability of the boards, as well as providing a striking aesthetic effect as the charring gives texture and relief to the boards. Depending on the timber used and the extent to which the charring is applied, a wide range of effects can be achieved. The traditional species used for this technique is Japanese cedar, but it can be used successfully on many softwoods. WEATHERING AND INSTALLATION CONSIDERATIONS Well installed cladding will provide many years of trouble- free enjoyment. However, we should always remember that timber is a natural product, and this should be reflected both in the installation techniques used and the expectations of the client. www.timberiq.co.za