Calk

Calk, more commonly spelled caulk, is a term used in carpentry, shipbuilding, and construction to describe the material and act of sealing gaps. As a verb, calk means to seal a seam or joint with a caulk or caulking compound to prevent water, air, or dust from passing through. When used in shipbuilding, calking specifically refers to packing the seams between wooden planks with a sealing material so the hull remains watertight.

The noun calk (or caulk) refers to the sealant itself. Traditional caulking in wooden vessels used oakum (tarred fiber) driven into the seams with caulking tools and then treated with pitch or tar. Modern caulks are synthetic or latex-based sealants, including silicone, polyurethane, polysulfide, and acrylic formulations, selected for adhesion, elasticity, and resistance to weathering. The term "calk" appears as an older or less common variant; "caulk" is the prevailing spelling in contemporary usage.

Common applications include sealing around bathtubs, sinks, windows, doors, and exterior joints to improve energy efficiency and prevent leaks. The process is typically performed with a caulking gun or by hand, using a compatible sealant and, if necessary, a primer or prep work to ensure adhesion. Proper caulking involves cleaning the joint, moistening porous substrates when appropriate, and allowing sufficient curing time.

See also: caulking gun, sealant, weatherproofing, joint sealant.