The manufacture and application of wood preservatives are governed by the Canadian Standards Association O80 standards: a collection of more than 32 different standards based on the commodity being treated (lumber, poles, piles, plywood, etc.). These standards dictate the wood species that may be treated, the allowable preservatives and the retention and penetration of preservative in the wood that must be achieved for the commodity or application. Similar American Wood-Preservers’ Association (AWPA) standards are also sometimes referenced.

Assay retentions: Retention, measured in pounds per cubic foot or kilograms per cubic metre, is the amount of preservative that must be impregnated into the wood to ensure that the product resists attack. It varies with preservative and intended end use.

Allowable wood species: Most of the softwoods used in Canada for general construction are also commonly treated. Species are often grouped, like S-P-F, on the basis of strength characteristics and harvesting; this does not mean that they are equally treatable. Most Canadian species are impermeable, or refractory, and must be mechanically incised to meet penetration standards.

Allowable preservatives: Effective preservatives are long lasting and highly resistant to leaching, volatilization, chemical breakdown and biological degradation. They are approved for commercial use on the basis of long-term field performance, accelerated testing and stake tests. Creosote has been used effectively against a wide range of organisms that attack wood for more than a hundred years. Penta has been proven in commercial use since 1930. CCA has similarly stood the test of over 60 years of use worldwide. The preservatives applied by commercial pressure treating plants are restricted-use pesticides; however, the finished treated wood is not considered a hazardous product.

Penetration: Penetration is the depth to which the preservative enters the wood. Using even the best pressure treating technology, it is difficult for the preservative to penetrate some species more than a few millimetres unless the wood is mechanically incised.

CSA O80 Wood Preservation Standards by Commodity

A reference table of the various CSA O80 standards by commodity is available on this website.

Assurance of Product Quality

The CSA O80 standards for wood treating are “results based”; the quality of the treated wood is easily measured by sampling after processing. The standards specify full instructions for sampling, penetration and retention tests and their analysis. Most treating plants have on-site labs in which they analyze core borings taken from the treated wood to determine how much preservative is present. Borings are also checked to see that the preservative has penetrated the depth of sapwood required in the standard. In the case of CCA, the degree of preservative fixation (also in the CSA O80 standards) can be detected and measured.