Drying of wood before treatment is necessary to prevent
decay and stain and to obtain preservative penetration.
However, for treatment with waterborne preservatives by
certain diffusion methods, high moisture content levels may
be permitted. For treatment by other methods, however, drying before treatment is essential. Drying before treatment
opens up the checks before the preservative is applied, thus
increasing penetration, and reduces the risk of checks
opening after treatment and exposing unpenetrated wood.
Good penetration of heated organic-based preservatives may
be possible in wood with a moisture content as high as 40%
to 60%, but severe checking while drying after treatment
can expose untreated wood.