Caulk is used for sealing joints, filling gaps, providing environmental protection, and firestopping. Caulk typically has an acrylic, silicone, or polyurethane base and is available as a single or multi-part compound. Common forms include gel, liquid, and paste.
Acrylic, or latex, caulk is water based and paintable. Higher-quality acrylic caulk contains a small amount of silicone for better adhesion. Silicone and polyurethane caulk are more appropriate for heavy-duty applications. Silicone caulk dries quickly, while polyurethane caulk can remain tacky for up to 24 hours; however, polyurethane resists abrasion better. Silicone caulk is suitable for use on glass, metal, and tile and remains flexible after drying. Polyurethane caulk performs better on wood. Both silicone and polyurethane caulk are waterproof.