Timber preservatives are conventionally used in two main ways.
Pretreatment, usually by vacuum or pressure methods
Remedial or in situ, usually by spraying or brush application.
Why treat?
During the second half of the last century, there was a virtual explosion of both sectors of the timber treatment industry. Timber became routinely pretreated, often as a purely precautionary measure. Remedial treatment of the smallest outbreak of woodworm or rot has become routine, with many Building Societies insisting on this before they will advance a mortgage.
Yet, all the evidence is that with good building design, timber treatment is rarely required.
Industry guidelines state that the 'need to treat' should always be established, and yet in practice routine treatment continues.
Toxic treatments
Over the last 50 years some incredibly toxic chemicals have been introduced into our homes and buildings in the cause of timber treatment. DDT, Dieldrin, Pentachloraphenol, Lindane, Tributyl tin oxide and Arsenic are some of the higly toxic and carcinogenic chemicals used to eradicate or prevent fungal and insect attack. Some are still being used.
Recently a new generation of timber treatments has been introduced with much lower acute toxicity. Permethrin, organic zinc compounds, IPBC, Dichlofluanid, Propiconazole are all much less toxic than the earlier treatments, but health and environmental concerns remain.
German studies suggest that Permethrin, one of the most common insecticides, is a carcinogen; it is also thought to be an endocrine disruptor, and has been implicated in reproductive system disruption in animals.
The big problem with many of these chemicals is that they slowly 'off-gas' out of the timber, yet no research has been undertaken on chronic very low level exposure in the home, or of the possible synergistic effect in combination with other chemicals present in the home.
All of these treatments require light organic solvents as carriers; these are implicated in health problems, and contribute to global warming.
Fences, sheds and outdoor timbers
The most common treatment for fences and other outdoor timbers is CCA treatment (one trade name for this is Tanalith treatment, producing tanalised timber). CCA describes the active ingredients of this treatment, Copper, Chrome and Arsenic. Although the manufacturers of course claim that this treatment is safe, and it is fully licensed for use in the UK, in some countries, notably Germany, it's use is severely restricted for safety reasons. Not only this, but there are major environmental implications in producing large quantities of Arsenic, impregnating timber with it, and then disposing of the timber afterwards.
Creosote is well known as an outdoor preservative and surface treatment, yet its hazards are greatly underestimated. It is highly toxic, a cause of skin cancer and probably other cancers and is only licensed for professional use in the US.
