Double vacuum process
A process used particularly for the impregnation of dry timbers that must retain dimensional accuracy for use in class 3 as windows and door frames, etc. However, other ranges such as constructional timber, cladding boards, wooden balconies, etc., are also treated in the double vacuum process.
In this so-called low-pressure process, the wood is first subjected to a short and relatively weak initial vacuum, after which the treatment vessel is flooded with preservative solution and reduced to normal pressure. Preservative intake is therefore greatly reduced compared to the vacuum pressure process. In the final vacuum, excess solution is removed to give the wood a relatively “dry” final surface.
Though exclusively solvent-based wood preservatives used to be used in this process, there has recently been an increase in the use of water-borne preservatives to reduce pollution caused by solvents.