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Biological performance of gypsum products containing borates
2000 - IRG/WP 00-30237
At suitable retentions borates have biostatic properties enabling them to be used for biodeterioration control in wood. They provide protection against decay fungi, mould, and termites, which are known to also attack gypsum products. Currently, many gypsum products contain added borates, which are used to improve physical and processing characteristics. Work examining the effect of borates at controlling biological attack in gypsum products is presented in this paper. Gypsum or gypsum board with different borate loadings was tested for its performance against dry rot, mould, and subterranean termites in order to see if current commercial levels of borates used in gypsum products would also render them resistant to these common types of biodeterioration. It was confirmed that the presence of borates significantly decreases the amount of biological attack found in gypsum products. From the results obtained it can be concluded that the addition of borates to gypsum products provides more than simple mechanical and processing improvements. For complete biodeterioration control however, especially against mould, higher retentions should be considered. This knowledge could have great significance in the near future, with moves to require termite resistant construction materials (including gypsum board) in some areas and the rising concern of illnesses associated with 'sick building syndrome' caused by in-house mould growth.
J L Fogel, J D Lloyd


Gypsum effects on ‘dry rot’ wood degradation as a function of environment
2007 - IRG/WP 07-10624
‘Dry rot’ fungi are a unique group of brown rot fungi that can degrade wood away from ground contact where other fungi fail to colonize. Successfully occupying this niche is partially due to efficient water and nutrient transport, but mobilizing elements, notably calcium (Ca) and iron (Fe), from adjacent building materials has also been implicated in their success. Here we report a series of trials with Serpula himantioides (previously ATCC 36335 S. lacrymans) degrading blocks in the presence or absence of Ca-rich gypsum (aka. drywall, plasterboard), using weight-loss as a measure of decay success. In previous work, pure gypsum did not facilitate dry rot in optimal growth conditions, but it was unclear if moisture or Fe-impurities could alter this dynamic. Commercial drywall was tested in a standard ASTM soil-block trial with spruce blocks and this Serpula wild-type isolate. Gypsum was also made from >99% pure CaSO4 and added in a sand-block trial with variable moisture. Finally, FeSO4 was used to amend gypsum to various Fe contents and the hardened material added to microcosms where spruce was decayed with no external Fe source. Weight-loss in blocks decayed in each experiment was statistically equal between treatments with and without the building material. These results corroborate previous findings, although this dynamic should be tested with other Serpula isolates and in an in-service trial to determine the role of building materials in dry rot.
J Schilling, J Jellison