Caulk or caulking is a material used to seal joints or seams against leakage in various structures and piping. The oldest form of caulk consisted of fibrous materials driven into the wedge-shaped seams between boards on wooden boats or ships. Cast iron sewerage pipe were formerly caulked in a similar way.

What is the purpose of caulking?

Caulk is a flexible material used to seal air leaks through cracks, gaps, or joints less than 1-quarter-inch wide between stationary building components and materials. For components that move -- doors and operable windows, for example -- weatherstripping is the appropriate material.

Why is it called caulking?

The word caulk comes from the Old Northern French cauquer, meaning "to press down." After you lay the caulk down over the seam you press it down by either running your finger over it or using a specific tool to force the caulk to settle into the hole you're trying to cover.