Timber Chemical Treatments

he chemical treatment of timber is a mystery to many hardware retail floor assistants. Are all treated timbers safe around humans? Are some chemicals unsuitable for use in food gardens? Are all timber treatments appropriate for use in marine applications? These are some of the “curly” questions that customers sometimes throw at retail staff, and it is important for all timber resellers to know the answers.One of the best information resources is the website of the Timber Preservers Association of Australia (TPAA) – visitwww.tpaa.com.auAHJtpalogoJune05

According to the website, there are three main categories of timber preservatives:

(1) Water-borne chemicals make up the lion’s share of preservatives for common domestic, commercial and industrial structures, both indoors and outside. Typical compounds in this category include Copper Chrome Arsenate (CCA), Ammoniacal Copper Quaternary (ACQ) and Copper Azole (CuAz). These kinds of preservatives offer protection from insects, including termites, decay and marine borers. Applications include fencing, decks, patios, landscaping works and posts. After decades of use in Australia, there is no evidence that CCA, for instance, has a negative impact on food crops through absorption via treated planter timbers or stakes – though the matter has been controversial in recent years. The TPAA holds the view that CCA-treated timber is safe when properly produced and used correctly.

(2) Oil-borne chemicals include the Creosote family of preservatives. These chemicals are for more heavy-duty protection against insect, decay and borer attack in utility poles, marine piles and railway sleepers. Typical products include Creosote and Pigment Emulsified Creosote (PEC).

(3) Light Organic Solvent Preservatives (LOSPs) are used for secondary treatments of timber products that have been sawn, cut or joined. These chemicals should only be used above ground. LOSPs include tributyl tin napthenate (TBTN) and numerous synthetic products like permethrin, deltamethrin, bifenthrin and cypermethrin for termite control.

AHJtarmaJune05Chemicals can be applied to timber in different ways. Methods include vacuum/pressure impregnation (for chemicals such as CCA and modified Creosote), double vacuum/immersion (LOSPs), as well as dip/diffusion methods (as seen in products like Polybor – a boron-based preservative used mainly for insect protection). Most dip processes, it should be noted, are designed for timbers with above-ground uses only.

The chosen method of treatment may alter the performance characteristics of a certain chemical, so check to make sure the treatment method suits the end-user’s building project.

Preserved timbers, when treated in the correct way using appropriate chemicals for end uses, should produce trouble-free and safe results.

As mentioned, the TPAA website is a good place to start to discern the basic chemical groups and functions.

By John Power