Chemical Wood Treatment
Chemical wood treatment is popular in both home and industrial uses, although environmental and safety concerns have reduced the types of wood preservative available. Copper-chromium-arsenic (CCA) was a popular timber treatment in the past, but the arsenic caused concerns. Today, alkaline copper quaternary (ACQ) and light organic solvent preservatives are more common in industrial settings.
Copper Chromium Arsenic
Copper-chromium-arsenic (CCA) preservative was used in the past, although it is much less common today. CCA was a type of water borne salt preservative, first used in the 1930s although usage was not popular until the 1950s.
Creosote was the first and most common wood preserver at the time CCA was used, but CCA was often preferred for indoor use. This was because unlike creosote it did not have a persistent odour. It was used for roof trusses and joists.
Today, environmental and safety concerns has led to decreased use of CCA as a timber treatment in the USA and Europe. The chemicals from the wood preserver are known to leach into the soil, and arsenic is a dangerous chemical for timber treatment plant workers to use.
The timber industry in the USA created a voluntary agreement with the Environmental Protection Agency to restrict the use of CCA. It is no longer used in residential construction, although it can be used in permanent foundations, shingles and a few other commercial applications.
In Europe, the use of CCA is also restricted and it cannot be used in domestic construction. It can still be used as a chemical wood treatment in applications such as bridges and electric power transmission poles.
Alkaline Copper Quarternary
Following restrictions on CCA usage, alkaline copper quaternary (ACQ) became widely used in the wood preservative industry. It does not contain the arsenic and chromium in CCA which were dangerous for safety and the environment.
The high levels of copper in ACQ wood preserver means it is not recommended to be used as a wood preserver if steel components will be attached to the timber. This is because the copper will corrode the steel. Stainless steel or double galvanised steel should be used instead.
Organic Solvent Preservative
In the 1960s light organic solvent preservative methods were developed. Active ingredients such as lindone and pyrethroid are dissolved into an organic solvent. These organic solvents are often white spirit or kerosene. This chemical wood treatment can also contain a binding agent, antibloom agents and water repellents.
Light organic solvents are often used as a wood preserver for building work. Unlike CCA, it does not cause physical changes in the dimensions wood, making it useful for components which need to be of a specific shape.
The use of light organic solvents has some environmental concerns, as they release volatile organic compounds. Timber treatment plants must minimise the escape of these chemicals.
Home and DIY Preservative
Chemical wood treatment can also be applied by home users, with brands such as Cuprinol and Ronseal being popular. There are many products available, which protect against weathering, rot and insect attack. Not all products are effective against every risk, and the user must carefully select the appropriate chemical wood treatment.
Home treatments can be applied via a spray or paintbrush. They are commonly used outdoors on fences and decking. These wood preservers can also be applied indoors to items such as stairs and furniture. At least two coats of the wood preservative are required.