What does caulking mean?
Caulking refers both to the waterproof material — typically a silicone, latex, or polyurethane compound — used to fill and seal the joints between surfaces such as bathtubs, sinks, window frames, and door casings, and to the act of applying that material. A continuous line of applied sealant is known as a bead, dispensed with a caulking gun, and its job is to keep water, air, and pests from penetrating gaps where two surfaces meet. The word has older roots in wooden shipbuilding, where caulkers drove fibers like oakum into hull seams to make them watertight. In modern usage, caulking carries practical, hands-on connotations of home maintenance and DIY repair rather than anything technical or formal. It is a common, unremarkable household term on both sides of the Atlantic, though British English often prefers alternatives such as sealant or mastic for the material itself. Knowing the word matters because failing or cracked caulking is one of the most frequent causes of moisture damage in buildings, making it a staple of any homeowner's vocabulary.
A waterproof sealant or filler compound used to close the joints and seams between surfaces so that they resist water, air, and dirt.
"Scrape out the old, crumbling caulking before running a fresh bead around the tub."
The act of sealing joints or seams, whether with modern sealant compounds or, traditionally, with fibers driven into a ship's planking.
"He spent Saturday afternoon caulking every window frame in the house."
Rarely pluralized; the mass-noun sense (the material) has no natural plural. A plural appears occasionally when referring to individual applications or beads of sealant, but writers usually avoid it.
"The inspector flagged several failed caulkings around the exterior trim."
Every tube of caulking in your bathroom traces back to a Latin word for heel — because early shipwrights drove oakum into hull seams by walking it in with their feet and tools called caulking irons.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of caulking
The word comes from the verb "caulk," which entered English in the late Middle Ages from Old North French "cauquer," ultimately deriving from Latin "calcare," meaning "to tread" or "to press," built on "calx," the heel. The connection is literal: shipwrights pressed and walked fibers into plank seams using tools called caulking irons. This Latin root also gives English words such as "calculus," "calcium," and "chalk," all originally tied to stone or pressing underfoot.
Related word forms
How caulking is actually used
In everyday American usage, "caulking" most often refers to the flexible silicone or latex sealant sold in tubes for home repair; British speakers more commonly say "sealant" or "mastic" for this material, reserving "caulk/caulking" largely for traditional shipbuilding contexts. As the -ing form of the verb "to caulk," it functions normally as a noun of activity.
Easily confused with caulking
"Calking" is simply an older or alternate spelling of "caulking" — same word, same meaning — not a different term.