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When sealants are exposed to water in the service environment a number of distinct phenomena may occur which can influence their performance, and may contribute to the failure of the sealant to perform the intended functions. The primary effects with which we are concerned are first, the absorption of water by the sealant, which may cause either softening or enhanced cure, depending upon the chemical nature of the sealant, its cure mechanism and state of cure at the time it is first exposed to moisture. Secondly, the diffusion of liquid water to the sealant/primer/substrate interfaces may impair the adhesive bond of the sealant to the joint surfaces. The laboratory evaluation of these effects is based on tensile testing in which the modulus and the extensibility of sealant test joints after varying durations of immersion in water are used as indices of performance. A system of performance evaluation based upon changes in these indices with water immersion is proposed, and discussed in relation to the results of BRE research results, and those of other workers in the UK.
test methods, wet environments, water absorption, adhesive bond, performance rating.