In 1980 The Swedish Wood Preservation Institute initiated an investigation to study the degradation of TBTO and possible fungal attack in double-vacuum treated window joinery in service during 5 years. A hospital in Gothenburg was chosen that was built during 1969 to 1976. Both untreated and double-vacuum treated windows of Pinus sylvestris were used. A brown alkyl oil type paint (Nordsjö system Rubbol S) was used for the surface coating. The double-vacuum treatment was carried out with Vascol EWR 52A according to a specification that in 1977 became preservation class B, Swedish Standard SIS 05 61 10, viz. at least 10 mm penetration of the sapwood and a retention of approximately 50 kg/m³ sapwood (approx. 0.1% m/m TBTO). In April 1981 approximately 200 windows, treated and untreated, were inspected. From 12 treated windows, then about 6 years old and exposed to weathering for 4.5 to 5.5 years, samples were taken for chemical and biological analyses, the objective being to find out to what extent the TBTO had been degraded but also to get an idea what species of micro-organisms had invaded the wood and if the protection against decay was still sufficient.

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