When it's done skillfully, caulking — or joint sealing — is almost invisible on a masonry exterior. But when it's botched, it can create a real eyesore. Worse, a poor caulking job can allow water into a building — with resultant damage, callbacks, lost time and money, and poor customer relations. Masonry joint sealants are called for in three situations: in an expansion or control joint, in a joint between dissimilar materials, and at the perimeter of an opening in the masonry surface. For the small general contractor, a single- family home or remodeling job that involves exterior masonry probably won't require enough caulking and sealing to make it worth hiring a specialty sub. But any joints, such