Caulking refers to the process of sealing a gap between two surfaces for the purpose of making it air or watertight. The word can be used as both a noun (when referring to the sealing substance) or as a verb (when referring to the act of sealing). There are hundreds of different types, but those most used in home repair include those made of acrylic latex, butyl rubber, and silicon.
Acrylic latex caulk (sometimes called painter's caulk): This type is used primarily as a sealant around windows and doors. It is available in a range of colors, and it can be painted over to match the adjoining surfaces. This type is easier to apply than silicon, and clean is easy with soap and water.
Butyl rubber caulk: This kind is the strongest and most durable. Its main use is to fill cracks in concrete and brick, but it can also be used to seal metal surfaces. Although Butyl rubber does not come in assorted colors, it can be painted to match surrounding surfaces. Clean up requires the use of a solvent.
Silicon caulk: When you want to keep an all-purpose caulk on hand, this is the type you will want. Silicon can be used on a wide variety of non-porous surfaces, from metal to plastic. Its best feature is that is remains somewhat flexible even after drying, so it is not prone to cracking due to temperature fluctuation. Silicon cannot be painted; however, it is available in a range of colors.
Besides the three basic types, there are many specialized varieties designed for specific tasks. Some of these include kitchen and bath caulk with a built-in mildew fighter; mortar caulk that holds up to high heat; roof sealant to repair minor leaks; gutter and flashing sealant; and asphalt sealant.
Caulk has traditionally been applied with a special caulking gun designed for that purpose. However, manufacturers these products have recently begun offering their products in squeeze tubes or pressurized can with an extended narrow tip so the do-it-yourselfer doesn't have to invest in a gun for just one simple repair job. Applying this material is a fairly simple task, although it may take a bit of practice to perfect drawing a uniform bead. Before applying any type, be sure that all surfaces are clean and dry.