The natural durability of our commercially grown species like Pinus and Eucalyptus, is low, rendering it susceptible to insect and fungal attack. It is imperative to preserve the timber.
There are two types of wood preservation; primary (industrial) and secondary (DIY). In primary preservation, wood is pressurized with an industrial chemical wood preservative e.g. CCA, TBTN-P or creosote. This process increases the long term durability and resistance to fungi and insect attack. Primary preservation is prescribed in SANS Standards, Compulsory Specifications and Building Regulations.
Secondary preservation is used for supplemental (preventative) and/or remedial (corrective) purposes and applied by hand, e.g. treating previously untreated timber or exposed ends of machined pressure treated timber. Protective wood sealers or varnishes are not regarded as secondary preservatives unless they contain active ingredients (biocide). Without active ingredients such finishes merely protect against weathering i.e. moisture and UV rays, and not fungal and/or insect attack.
Primary preservation of timber is categorised into ‘H’ classes for different end-use applications.
| H CLASSES | PRESERVATIVE TYPES | TYPICAL END-USE APPLICATIONS | PROTECTION AGAINST |
| H2 – Dry interior above ground | CCA, CuAz, ACQ and BoronTBTN-P and ZP | Roof trusses frame wall construction interior doors and joinery | Insect attack |
| H3 – Exterior above ground | CCA, CuAz& ACQCreosote | Decking, cladding, exposed structural | Fungal attack and insects |
| H4 – Exterior in-ground | CCA, CuAz& ACQCreosote | Timber used in the ground Poles used structures, fencing, landscaping and garden features | Fungal decay and insect attack |
| H5 – Fresh water & heavy wet soil contact | CCA, CuAz& ACQCreosote | Jetties Walkways | |
| H6 – Marine | CCA plus Creosote | Jetties, quays, marine walkways, retaining walls and barriers |
Be sure to choose the correct H class of treated timber for your intended application and apply remedial preservative to all cross-cut and exposed areas (except for ground, fresh water or marine applications). Apply a suitable wood sealer when the natural non-weathered look of the exterior timber is desired.
When planting a pole or post do not plant them inside an encapsulated concrete base. Instead, use a ‘collar’ or compacted stone and soil with or without a solid (cured) concrete base.
How to plant a pole/post
As a safety precaution when machining CCA treated wood, wear a dust mask, gloves and safety glasses to protect your eyes. Do not make baby toys, furniture, food utensils or store food or water in containers made from CCA treated wood. CCA treated wood should also not be used in beehives or used for animal litter where it may become a component of animal feed.
Treated timber waste is not regarded as hazardous waste material and should be disposed of at a registered disposal site. Do not burn treated wood off-cuts and do not use it for firewood or for food preparation.
For more information on wood preservation in South Africa, please contact South African Wood Preservers Association (SAWPA) on:
Telephone: (011) 974-1061 or 078 144 6213
E:mail: admin@sawpa.co.za
Website: www.sawpa.co.za.
