Characterization of fungal attack on existing wooden facades and other surfaces

The aim of the project has been to study the growth of microorganisms on selected wooden surfaces representing different aspects of construction and microclimate.

Studies of microbial occurrence and variation were carried out with respect to

1. a microclimate with relatively low moisture content and growth on wood components from an exterior wall of a demolished school in Gothenburg,
2. test object of cross-laminated timber (CL) found under roof during November-May at LTU Skellefteå. The object was designed as a chair manufactured at Martinsons and exposed outdoors at Kroksjön in June-September (IPOS/Bioinnovation).
3. Discarded cross-laminated timber (CL) board exposed for a long time in a more extreme and humid microclimate with moisture leakage but with limited air access and air exchange: different positions on two horizontally lying cross-laminated timber (CL) boards separated by straw and stored wrapped outdoors for 3 years at the Martinsson wooden bridge factory in Kroksjön outside Skellefteå.

Samples were taken with sterile cotton plugs by swabbing sample surfaces on the various test objects, cultivating them in petri dishes and studying the presence and variation of microorganisms morphologically with a light microscope and using staining reagents. During the project, the sample method was also developed regarding: a) dilution before cultivation, b) the number of replicates c) cultivation of specific colonies for improved characterization and for future use and characterization of the species of fungal colony.

Especially in cases of high contamination, dilution of the isolated sample before culturing was found to be important in order to more reliably characterize the presence and variation of microorganisms. An instructional film for sampling for microbiological characterization of wooden surfaces was prepared and used by Derome and Martinsons. It should, however, be supplemented with more information about the risk of contamination of samples when sampling is carried out by personnel without further knowledge of microbiological sampling.The variation in colony formation during cultivation, which in some cases was more significant between replicates, shows the importance of including sufficient numbers in studies, especially if small differences between sample areas can be assumed. It is therefore important to carefully plan the experimental design when manually characterizing each sample with a microscope. Techniques for genetic characterization of biological material are developing at a high rate and one way to make the characterization of microbiological attack more complete and at the same time easier would be to develop such techniques.

Area: Materials & processes
Budget: 480 000 SEK
January 2021 - March 2022
Project leader: Olov Karlsson, Luleå University of Technology
Funding: This subproject was funded by TCN