What is caulk?
Updated August 2026
Caulk is a flexible sealant gunned from a tube to close the joints where two materials meet, keeping water and air on the correct side of the wall. It is neither glue nor filler. A good bead stays elastic for years and stretches as the joint opens and closes with temperature, which is why the right product in a 1/4-inch gap outlives the wrong product every time. Four families cover nearly every job around a house: siliconized acrylic latex, 100 percent silicone, polyurethane, and butyl rubber.
Where it is
Anywhere two different materials meet and neither one sheds water on its own. Outside, that means the perimeter of every window and door where trim meets siding, the vertical seams at corner boards, and every penetration through the wall: hose bibs, dryer vents, electrical and cable entries, exterior light fixtures. Inside, it is the tub-to-tile joint, the shower corners, the countertop backsplash, and the line where trim meets drywall. An average house carries 200 to 400 linear feet of exterior caulk joints, which is why the yearly walk-around always finds something.
What it does
Two jobs: keep bulk water out of the wall, and stop air from moving through it. Both fail visibly. Exterior beads shrink, harden under UV, and either split down the middle or peel cleanly off one face, typically after 5 to 10 years for acrylic latex and 15 to 20 for quality silicone or polyurethane. Bathroom beads run a shorter clock, mildewing and lifting in 2 to 5 years because they live wet. Geometry decides more than brand does: a joint should be about twice as wide as it is deep, gaps over 1/4 inch need foam backer rod behind the bead, and anything wider than 1/2 inch calls for trim or expanding sealant rather than more caulk. A failed window bead is a quiet water path into sheathing and framing, and once paint bubbles on the inside, the bill is measured in thousands: what failing caulk around windows costs.
Maintenance
Walk the outside of the house once a year in spring and press every reachable bead with a thumbnail. Anything hard, cracked, or separated from one face gets cut out and replaced. You are re-sealing sections, not the whole house, which makes it a Saturday and about $30 in tubes. One 10-ounce tube lays 25 to 30 feet of a 1/4-inch bead. Work above 40 degrees and leave 24 dry hours for it to skin over. Intervals are in how often to recaulk the exterior, and technique in recaulking exterior windows and doors and recaulking a bathtub.
What it costs to replace
A replacement caulk bead runs about $5–12 a tube in materials, $200–600 for a handyman to re-seal the windows and doors on an average house, or $150–300 for a tub and shower re-caulk.
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Frequently asked questions
What kind of caulk should I use where?
Match the product to the surface. Siliconized acrylic latex, $4–8 a tube, is paintable and belongs on interior trim and painted exterior wood. Pure silicone, $8–12, grips glass, tile, and metal and shrugs off standing water, but nothing will paint over it. Polyurethane, $8–14, handles masonry, driveway edges, and joints that move. Butyl rubber goes in gutters and flashing seams. The repeated mistake is a paintable product in a tub, or silicone on wood you intended to paint.
Can you caulk over old caulk?
Not with any expectation that it holds. Fresh sealant bonds to the old bead, and the old bead is already losing its grip on the substrate, so the whole sandwich peels within a year or two. Cut it out with a utility knife or a removal tool, scrape the joint clean, wipe with denatured alcohol, and let it dry. Removal takes longer than laying the new bead, which is precisely why so many houses wear three layers of it.
Where should you never caulk?
Anywhere water needs a route back out. Leave the weep holes at the bottom of brick veneer and vinyl window frames open, leave the bottom edge of horizontal siding laps alone, and leave the underside of a window sill and its bottom trim uncaulked so anything that gets in can drain. Never substitute caulk for flashing on a roof. Sealing those spots converts a wall that drains into a wall that stores water.
How long does exterior caulk actually last?
Plan on 5 to 10 years for acrylic latex and 15 to 20 for quality silicone or polyurethane, less on any south or west elevation taking full sun. Movement shortens it too: joints around a door that gets slammed, or on siding that grows an eighth of an inch on a hot afternoon, work the bead harder than a static seam. Inspect yearly, touch up a few spots each spring, and expect a full pass every decade.