Source: MASONRY CONSTRUCTION MAGAZINE
Publication date: December 1, 1996
By Christine Beall
The sealants used to provide weather protection in masonry expansion and control joints form the final link in the cladding envelope. Successful movement joints that are watertight and durable require proper joint design and construction; adequate joint sizing; appropriate product selection; and careful sealant installation.
The choice of sealant material should be based on performance, aesthetics, and durability. Only high-performance elastomeric sealants, such as polysulfides, urethanes, and silicones, should be used in masonry control and expansion joints. These sealants are covered by ASTM C 920 Standard Specification for Elastomeric Joint Sealants.
The movement capability of sealants is closely related to modulus of elasticity, defined as the ratio of the force (stress) needed to elongate (strain) a sealant to a certain point. Many sealants are available in single-component and multi-component formulations. Single-component sealants are supplied ready for application and require no mixing. Multi-component sealants are mixed at the jobsite just before application.
To maintain movement capability over an extended service life, sealants must have good elasticity in cyclic movements. Elasticity is a measure of the sealant's ability to recover its original shape after elongation or compression.
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