What Type of Caulking Should I Use to Seal Cracks in the Wood Siding on an Old Garage?

About Marine Caulk

• Marine caulk is designed for use on ships and is waterproof. There are three kinds of marine caulk, each with its own use. Silicone caulk is used as a sealant for plastic or temporary gasket material. Polyurethane forms a permanent bond. This makes it unsuitable for wood that may require replacement. The third variety, polysulfide caulk, can't be used on plastic, but can be used on wood, including wood that eventually requires replacement.

Characteristics of Polysulfide Caulk

• Don Casey, boating expert for BoatUS -- the Boat Owner's Association of the United States -- calls polysulfide caulk "the most versatile of marine sealants." Polysulfide caulk is synthetic rubber. Recommended for use on teak decks and between hull planks, it adheres strongly to the surfaces to which it is applied. It can be sanded and painted without compromising its ability to seal a seam.

Durability

• Polysulfide and polyurethane caulks lasted longer than silicone in a study conducted by "Seaworthy" magazine, the official publication of BoatUS. "Seaworthy" polled a group of 30 boat repair specialists about the staying power of the three kinds of caulk. According to the study, 59 percent of the respondents said that polysulfide caulk lasted between six and 10 years, when used correctly. Only 43 percent of those surveyed reported similar performance from polyurethane caulk and only 17 percent of the group surveyed said that silicone caulk lasted that long.

Availablity

• Polyurethane and silicone caulks are found in both the home improvement and sports equipment sections of discount department stores. Polysulfide caulks, however, are easier to find in boating supply houses. If you aren't located near the water -- or a boating store -- you can still enjoy the advantages offered by one variety of marine caulk or another.