Mechanism of infection of fir wood joinery; Part 1: Exposure conditions, moisture content and permeability

In Croatia the primary raw material for joinery production is fir wood (Abies alba Mill). The L-joints made of home-grown fir sapwood and prepared according to EN 330 were used to establish the colonisation and infection of micro-organisms in comparison with the performance of untreated and 1% TnBTO treated L-joints by ten-minute immersion. The L-joints surfaces were treated with two types of coat, and exposed on three different climate sites in Croatia: Zagreb, Zalesina and Rovinj. The first type of coat was alkyd paint and the second was a stain in three different colours: white, brown and black. The untreated L-joints were examined after 1, 2, 3, 4, 6, and 12 months and treated after 12 months of exposure. The influence of the climate, and the type of coat of paint was decisive on the moisture contents, permeability and colonisation. In Zalesina, a mountain site with the highest average air humidity and a great amount of precipitation colonisation was fastest and strongest due to the largest average moisture contents and permeability. The least moisture content and the least permeability occurred in the L-joints exposed in Rovinj, a site on the Adriatic coast, particularly on those coated with the darker stain. It was due to the well known vaporous diffusivity of the stains and the fact that Rovinj had the highest number of sunny days during the first two months of exposure when the dark stain surfaces absorbed many more of the sun's heat rays which caused accelerated seasoning, lower moisture contents and a lower increase in permeabilitv. The influence of the coated colours later was not significant. Between the average moisture content and an average permeability of the untreated and treated L-joints coated with stain there were no signifficant differences. In comparison of untreated and treated L-joits coated with alkyd paint greater moisture contents and greater increase in permeability occurred on the untreated L-joints.