Construction World September 2016

WOOD CONSTRUCTION

Understanding WOOD PRESERVATION There are two types of wood preservation; primary

Safety precautions and warnings

(industrial) and secondary (DIY). Primary wood preservation is the impregnation of timber with a wood preservative chemical like CCA, Creosote, Borate, TBTN-P or Azole Permithrin, using prescribed industrial processes.

When sanding and sawing CCA treated wood wear a dust mask and safety glasses, and work in a well-ventilated area. Wash work clothes separately. Treated wood must not be used for: firewood, baby toys, furniture which may be chewed on by infants, food utensils or storage containers, beehives, nor should treated wood shavings or sawdust be used for animal litter or where it can become a component of animal feed. Disposal Treated timber waste is not regarded as hazardous waste material; however, treated wood off-cuts and waste should not be allowed to accumulate, but should be disposed of at a registered disposal or landfill site. It is important not to burn treated wood off-cuts and waste or use it firewood for food preparation, as this will allow the release of chemicals, which are tightly bound to the wood, into the smoke. The ashes may also contain residual chemicals.

tions). Do not plant poles inside an encapsu- lated concrete base. Instead, use a ‘collar’ or compacted stone and soil with or without a

This increases the durability and resistance to fungal attack, wood borers and termites. This pre-treatment prior to use is

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solid (cured) concrete base. How to plant a pole

prescribed in SANS standards and mandatory compliance is regulated through regulations and compulsory specifications, along with third party product certification. Supplemental or remedial preservatives on the other hand contain biocides which are included in mainly solvent or oil based solu- tions (in some cases wood finishes or sealers), and are applied in a DIY setting by brush, paint or spray to stop further attack. These require an on-going maintenance program to remain effective as it is merely a surface application with minimal penetration. It’s important to note that most exterior wood sealers or varnishes, contain no biocides and only protect against weath- ering, moisture and UV rays, but not against fungal and insect attack and should rather be referred to as protectants than preservatives. Why preserve timber? The natural durability of our commercially grown and used plantation species like Pinus and Eucalyptus (gum), is low, rendering it susceptible to insect and fungal attack; there- fore it is imperative to preserve the timber. Choosing the correct treated timber The following SANS standards apply to treated timber: • SANS 457 – droppers, guardrail posts, building, fencing and agricultural wooden poles • SANS 753 and 754 – wooden poles for transmission and telephone lines. • SANS 1288 – All other preservative treated timber, e.g. sawn structural, flooring, etc. These standards specify a Hazard Class system (H Classes), which categorises treated timber into different end-use applications based on different exposure conditions and risk of biological attack. Product use information Be sure to choose the correct H class timber for your intended application and apply remedial preservative to all cross-cut and exposed areas (except when in contact with the ground, fresh water or marine applica-

Choose the corect hazard (H) class

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H6 – High Hazard: Ptolonged immersion in sea water (marine piling, jetty cross-bracing, landing steps, reatining wall, etc.)

H5 – High Hazard: Outside in contact with heavy wet soil or in fresh water (piling, substructure for walkways and jetties, vineyards, etc.)

CONSTRUCTION WORLD SEPTEMBER 2016