What are the best sealants to use in masonry expansion joints?
When selecting a sealant, As consider the building design and the expected movement of the joints. Also, it's often a good idea to call the technical service department of a sealant manufacturer. In general, I recommend using two-part polyurethane sealants. The new high-performance silicone sealants can actually outperform the polyurethane sealants; however, silicone sealants tend to get dirty much faster. Polysulfide sealants also can be used but they tend to be vulnerable to surface cracking and checking. Butyl and acrylic sealants typically don't perform adequately in most masonry expansion joints. Two-part polyurethane and multicomponent sealants need to be thoroughly mixed to perform properly. The minimum amount is usually 5 gallons. If only a small quantity of sealant is needed, I'd use a one-part polyurethane sealant.