Paintability and gluability of wood treated with arsenic-free and chromium free preservative treatments
L Podgorski, G Legrand
The objective of this project was to study, in comparison with traditional CCA treatment, the paintability and gluability of wood treated with arsenic-free and chromium-free preservative treatments.
Four formulations, all certified CTB P+, were selected in accordance with their representativeness of the preservative product market: one CCA reference formulation and three chromium and arsenic free formulations (S1, S2, and S3). The species of wood chosen was the Scots pine.
A wettability study has shown that the four preservative treatments lead to very different surface characteristics. CCA and S1 treatments make wood hydrophobic whereas S2 and S3 make wood hydrophilic.
The paintability phase was carried out on six types of coatings including waterborne and solventborne products, paints and stains. The performance of the coatings on the different treated woods was characterised by artificial and natural weathering tests.
For the paints tested, the overall appearance of the test specimens after weathering was the same irrespective of the wood preservative. As regards the transparent coatings tested, the general appearance of the test specimens after weathering is generally better on CCA treated wood.
However, the adhesion testing showed a tendency toward poorer adhesion for coatings on wood treated with new generation preservatives.
The objective of the gluability phase was to qualify:
Glue-laminated treated northern Scots pine with RPF, MUF and PU type structural adhesives, used for load bearing structures,
Glue-laminated treated regional Scots pine with an EPI type non-structural adhesives, used for joinery.
As such, the initial mechanical performance of the different glue bonds was evaluated through shear testing by compression. The durability of the assembly was evaluated by delamination testing.
The wood treated with new generation products therefore displays satisfactory gluability with RPF, MUF and PU type structural adhesives. Results are more variable with EPI type non-structural adhesives.