Terms of the Trade: What Is Mastic Sealant? Terms of the Trade: What Is Mastic Sealant?
Mastic sealant is a liquid substance used to join two materials together or to protect the area where it's applied. Notable is its ability to bond to almost any material, including glass, metal, aluminum, concrete, and marble. It maintains a flexible bond after it dries, but isn't meant for use in joints that have a lot of movement.