Never out of style in kitchens and bathrooms, tile has endured through the decades. Over time, however, small spaces can open up between tiles, and in moist environments that's an invitation for mold and mildew to gather behind the walls. There are several types of caulk that can be used in such situations. Ideal for wet environments, 100 percent silicone caulk and siliconized acrylic caulk form a durable, watertight seal. Mold- and mildew-resistant silicone caulk is made for nonporous surfaces like ceramic, glass, and metal, while waterproof siliconized acrylic caulk works well on tubs, tile, glass, and ceramic tile surfaces.