Treatability of different wood types

The treatability of the various wood types has an important role to play, particularly for the impregnation of timbers in the vacuum pressure process or the double vacuum process. Depending on the treatability of the particular wood type, the treatment parameters are selected to ensure the wood receives optimum protection from the process.

In the EN 350-2 standard "Natural Durability of Solid Wood", the treatability of the various wood types is also listed. There are altogether 4 treatability classes:

Treatability classDefinitionDescription
1permeableeasy to treat
2moderately resistantmoderately easy to treat
3resistantdifficult to treat
4extremely resistantvery difficult to treat

In the vacuum pressure process, mainly coniferous wood types are treated, some of which have very different treatability levels:

Wood typeSapwoodHeartwood
Spruce33 – 4
Fir22 – 3
Douglas fir2 – 33 – 4