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
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