Protecting timber

The ecologically balanced first step approach to timber preservative is that if it doesn’t need it, don’t use it. Nevertheless, treatment of timber allows the use of more perishable timber species and those parts of a tree (sapwood) which are more prone to decay. This allows the forestry industry to minimise waste and maximise its resources and reduce pressure on the more durable and higher value species. Modern chemical treatments are much more environmentally friendly than in the past, when aggressive toxic chemical mixtures such as copper, chromium and arsenic salts make sure that the particular type used was suitable for your wood. Other safe alternatives to CCA now include ammoniacal copper quartenary (ACQ), copper azole and copper citrate. or Chromate Copper Arsenate (CCA), pentachlorophenol (PCP) or creosote were in common use. Nowadays, boron based compounds such as borate oxide (SBX) are well known, non toxic preservatives, but you need to

Any wood used in a timber frame dwelling which is likely to come into contact with moisture, wood damaging insects, the weather or external climate conditions, must be treated to combat the likelihood of rot, mould or decay.

Therefore, all timber members in the external walls and in the ventilated and drained cavities of timber frame houses should be treated with suitable preservatives and processes. This should include sole or floor plate timbers of internal walls and any timber in contact with the damp proof courses (DPCs) or damp proof membranes (DPMs). Any timbers which have been cut or trimmed on site must have their ends carefully treated with preservative. The treatment process is as important as the preservatives used and the best type of process nowadays uses a system of impregnating the timber under a combination of vacuum and pressure, in a large treatment vessel.

Correctly referred to as Vacuum Pressure Impregnation (VPI) although it can be known by various names, the process involves placing a stack of timber in the tank, pumping all the air out, introducing the preservative under vacuum conditions and then applying hydraulic pressure to force the preservative into the timber cells which had been evacuated of air under the vacuum process.

There can be much confusion around the names of the treatment processes, where different names often mean different things to different people, so look at exactly what type of process the timber producer is using and whether it meets the specifications of the timber that you need.

On site, know your products. I once found a joiner treating the cut ends of solid timber with a liquid from a container of a well-known brand of timber