Adhesion between paints and wooden substrates: Effect of pre-treatments and weathering of wood

The effects on adhesion between paints and wooden substrates due to pre-weathering (delay in painting), treatments of wood during pre-weathering and the moisture content of substrates were monitored. The adhesion was studied by means of a torque test.
Wooden panels were untreated, or treated with unpigmented, penetrating wood preservatives or treated with pigmented strain, and pre-weathered for various periods. The panels were then painted and subjected to further exposure. The adhesion of the paints was determined at two relative humidities.
Pre-weathering of 12 weeks impaired the adhesion significantly when emulsion paints were used, and when the wood substrates were untreated or treated with the unpigmented treatments during the pre-weathering.
When the substrates were protected with a pigmented stain prior to painting, a longer delay before painting could be accepted. Also, wood substrates with higher moisture contents reduced the adhesion of the emulsion paints.