Influence of coating and colour on bacterial colonisation of fir-wood L-joints

Silver-Fir (Abies alba, Mill.) sapwood L-joints coated with high build alkyd paint (HAP) and medium build alkyd stain (MAS) in white, brown and black colour were exposed in Zagreb and examined after 1, 2, 3, 4, 6, 12 and 36 months of exposure. The highest bacterial colonisation was recorded in HAP L-joints. Significantly lower bacterial colonisation always occurred in MAS L-joints. This is particularly evident during the first three months of exposure. Water vapour permeability of stains and the fact that black stain surfaces absorbed much more heat from the sun provided accelerated seasoning, lower moisture contents and lower bacterial colonisation. The possible influence of coating colour only occurred during the first three months of exposure, and later on it was more or less insignificant. In general, L-joints coated with dark colour were less infected and colonised by bacteria. The intensity of bacterial activity (BA) varied significantly within the same group of L-joints due to well-known non-homogenous structure of Silver-Fir wood.