Timber iQ October - November 2019 // Issue:46 | Page 43

FEATURES Wood used in exterior applications such as decking or walkways needs to be both strong and durable. One option for improving timber durability is to alter its physical properties through impregnation, heat treatment, or a combination of these processes. This works for certain applications but in most cases the overall costs end up as high as for tropical hardwood alternatives, and producers require large capital investments. “With this in mind, Merensky has turned its focus to surface treatments, and understanding what best suits our timber in various applications, so that we can give practical advice to our customers,” says Dowse. “Our exposure testing covers the majority of South Africa’s commercially-available surface treatment options, including oil-, solvent- and water-based alternatives. Our testing also covers combinations of these as well as the use of additives such as waxes and UV-protective colour pigments.” Dowse says the Merensky Research team has drawn up various conclusions through this testing, which form the basis of its recommendations to customers. LOCATION AND CLIMATE Samples tested and exposed in Cape Town (Western Cape) degraded much faster than those tested and exposed in the more tropical Tzaneen area (Limpopo province). Treatment selection therefore needs to take into account environmental factors such as humidity, wind, UV index, rainfall and wet seasons. TIMBER SURFACE-TREATMENT TESTING Merensky walkway exposure testing of various surface treatments under high foot traffic conditions. APPLICATION Certain samples that weathered very well on exposure racks did not fare as well during walkway tests, when subjected to everyday use and wear and tear. Factors that play a role here are physical abrasion (such as foot traffic on a walkway or deck), orientation (whether the surface is flat or vertical, in the sun or shade) and construction (such as exposed areas at joints, or moist areas under decks). WOOD QUALITY During testing, our higher-quality or select-grade lumber was identified as least likely to exhibit surface checking, splitting or cupping – all features that increase the risk of water ingress, which has a damaging effect on timber. Exposure to the elements, as well as drying and treating the wood, can further develop these defects, especially in lower-quality timber. TYPE AND DENSITY OF WOOD Not all treatments can be universally applied on all species and variations of wood. The Merensky exposure tests revealed that some treatments formed a good-looking surface layer after treatment but did not penetrate the wood surface layer – especially on higher-density hardwoods. These may therefore start to flake quickly when treatments dry out or are exposed to high-wear conditions. MAINTENANCE REQUIREMENTS Film-forming surface treatments such as varnishes were shown to start flaking or peeling when not maintained for prolonged periods and, in most cases, a complete removal of the treatment was required in order to remedy this. Most manufacturers recommend that a fresh coat be applied, www.timberiq.co.za Test samples from the exposure racks after 18 months’ exposure showing clear signs of flaking due to a lack of bonding to the hardwood surface. // OCTOBER / NOVEMBER 2019 41