The water absorption and water vapor permeability of clear organic coatings

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Journal titleOfficial Digest
Pages232243; # of pages: 12
Subjectwaterproof coatings; paintwork; water absorption; permeability; water vapor; phenolic varnish; alklyd paints; epoxy coatings; urethane (elastomere); Buildings
AbstractThe three factors which degrade a clear coating or the wood substrate are light, water, and oxygen. The paper covers the transmission and absorption by clear organic coatings of one of the agents--water. The range of materials tested include pure phenolic varnishes, air-drying alkyds, cold- cured epoxies, and two types of urethanes. Absorption was found not to vary with composition and was extremely low for all the unpigmented materials. Both wet and dry cup permeabilities were measured. At equal film thickness permeability was not affected by the number of coats. Permeability correlated very well with composition and increased with increasing oil content of phenolic varnishes and alkyd resins. It decreased with increasing molecular weight of a series of varnishes. There was, however no correlation between permeability and durability. An amide- cured epoxy which had the lowest permeability also had a low durability rating. Tung oil-p. phenyl phenolic varnishes which gave the best exterior exposures were intermediate in permeability. The ratio of wet cup to dry cup permeability was close to one indicating the materials are not water sorbing. The results show that permeability and water absorption are not related.
Publication date
AffiliationNational Research Council Canada; NRC Institute for Research in Construction
Peer reviewedNo
NRC number7948
NPARC number20375847
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Record identifierfd52e780-ff1c-454e-bd15-889796699bc1
Record created2012-07-23
Record modified2016-05-09
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