Ask us anything about caulk

On the shelf, less than the labels suggest. Traditionally, caulk means a paintable, less stretchy product (think acrylic latex) for filling interior gaps, and sealant means a higher-flex, higher-performance product (silicone, polyurethane, hybrids) for joints that move, get wet, or live outdoors. Manufacturers use both words loosely, so read what the tube says it's for instead of what it's called.

The long version: Caulk vs. sealant vs. grout vs. putty.

100% silicone labeled for kitchen and bath, with a mildew-resistant formula. It's waterproof, stays flexible as the tub moves, and doesn't break down under daily soaking. Our pick is GE Silicone 2 Kitchen & Bath. More in the bathroom guide.

A paintable acrylic latex or siliconized acrylic latex. It tools easily, cleans up with water, and disappears under paint. DAP Alex Plus is the painter's default. If the gap opens and closes with the seasons, step up to a stretchier product like Sashco Big Stretch.

Not if you want it to last. Exterior joints face UV, rain, and big temperature swings, and interior-only caulks tend to crack, shrink, or wash out. Many tubes are labeled interior/exterior, which is fine; a tube labeled interior only belongs indoors.

It's acrylic latex with some silicone added for better adhesion, flexibility, and water resistance. It's still paintable and still cleans up with water, but it isn't the same as 100% silicone, and it won't hold up like silicone in joints that sit in water. See siliconized acrylic on the types page.

Eventually. Many clear caulks go on white or cloudy and turn clear as they cure, which can take days for thick beads or solvent-based products like Sashco Lexel. Clear also shows everything: voids, dirt trapped in the joint, and the shadow of old caulk you didn't remove. Prep matters more with clear, not less.

Match whichever the eye reads as the joint. In tile work that's usually the grout, which is why color-matched sanded caulks like Polyblend Sanded Tile Caulk exist. Against trim you'll paint, use white paintable caulk and paint over it. Where a tub meets tile, white or clear silicone is the classic choice; when in doubt, go slightly lighter rather than darker.

They describe how far a cured sealant can stretch and compress, as a percentage of the joint width, without failing. The rating system comes from ASTM C920: Class 25 handles about 25% movement either way, Class 50 about 50%, and so on. Higher is better for exterior joints, siding, and anything that moves with the seasons. See joint movement in the glossary.

Most unopened tubes are good for roughly a year, sometimes longer; the tube or packaging usually carries a date or batch code, and the manufacturer lists the shelf life. Store it somewhere cool, dry, and above freezing. Once opened, seal the nozzle (a nail, a cap, or tape) and plan to use it within weeks. If it comes out lumpy, stringy, or won't cure, it's done.

Grout fills the spaces between tiles and cures hard. Caulk goes where two planes meet or where things move: inside corners, the tub line, the joint between countertop and backsplash. Grout in a moving joint cracks; caulk in a field of tile looks wrong. Use each where it belongs. More in Caulk vs. sealant vs. grout.

Clean and dry the joint, run painter's tape along both sides, cut the nozzle smaller than you think, keep steady pressure and a steady speed, tool it once, and pull the tape right away while the caulk is wet. The full walkthrough: How to lay a perfect bead.

About 45 degrees, with an opening a little smaller than the gap. The angle lets you hold the gun at a comfortable slant and press the bead into the joint. You can always cut more off; you can't glue it back. Then puncture the inner foil seal with the gun's poker or a long nail.

Both work. Pushing the bead ahead of the nozzle tends to drive caulk deeper into the joint; pulling is easier to control and often neater for beginners. What matters most is a consistent angle, speed, and trigger rhythm. Pick one and practice on a scrap board.

Most tubes list a maximum joint width, often around half an inch, and many want joints no deeper than about half an inch. For anything deeper than roughly a quarter inch, press in backer rod first so the caulk has the right depth. Much wider gaps usually need a different fix, like trim, filler strips, or a high-movement sealant over backer rod. Check the tube.

A foam rope you press into deep joints before caulking. It sets the depth of the bead, saves caulk, and keeps the caulk from sticking to the back of the joint, which lets the bead stretch properly (see three-sided adhesion). Use it when a joint is deeper than about a quarter inch. Full story: Backer rod and joint design.

Almost never. New caulk bonds poorly to old caulk and not at all to silicone residue, so you get a thicker bead that fails sooner. Remove the old bead, clean the joint, and start fresh. How-to: Removing old caulk.

Run a gloved fingertip, a caulk tooling tool, or the back of a plastic spoon along the bead in one steady pass, pressing it into both sides of the joint. Latex tools nicely with a slightly damp finger. For silicone, some pros mist a little soapy water on the tool so it glides; keep it off the edges where the caulk needs to bond. Tool once, then leave it alone. See tooling.

Many latex caulks want at least about 40°F (4°C) and rising, with no rain or frost in the forecast. Silicones and some solvent and hybrid sealants can go on colder. Hot sun can make caulk skin too fast and bond poorly. The tube lists the application range, and the surface temperature matters more than the air. More: Temperature, humidity and cure time.

A standard 10.1-ounce cartridge runs roughly 25 to 30 feet of a quarter-inch bead, and much less for bigger beads, since volume grows with the square of the bead size. Buy one more tube than you think; running dry halfway down a joint leaves a visible splice. Our tube calculator does the math.

Work from the top down so gravity helps instead of fighting you, keep the nozzle tight to the corner, and tool the whole run in one pass. For inside corners, a slightly concave bead that meets both surfaces cleanly looks best and sheds water.

Usually uneven trigger pressure, moving too fast, or a nozzle opening that's too small for the gap. Squeeze steadily and let the bead lead you. An air pocket in the cartridge (or an inner seal you didn't fully puncture) causes sputtering, too. A dripless gun, or popping the pressure release when you stop, keeps it from oozing.

Check the tube. Many silicones advertise water-ready times from about 30 minutes to a few hours, while siliconized acrylics can need a day or more. Full cure takes longer than water-ready, especially for thick beads. Waiting a full 24 hours before a long hot shower is the safe default.

Dry to the touch (or skinned) means the surface won't smear. Paint-ready means the surface can take paint without cracking it. Fully cured means the caulk has hardened all the way through, which can take days or weeks for deep beads, because most caulks cure from the outside in. The tube lists each time. See cure time.

Not pure silicone. Paint beads up, peels, or never really sticks. Some "paintable silicone" and hybrid products exist, and results vary by paint, so test first. If a joint will be painted, choose a paintable caulk from the start. See 100% silicone.

For painted trim, the usual order is prime, caulk, then paint the final coats over the caulk so the joint and the trim match. With silicone (which you can't paint), paint first and caulk last.

The bead may be thick, the weather cold or humid, or the tube old. Some products stay slightly soft by design: acoustic sealants never fully harden, and very stretchy caulks like Big Stretch take their time. If it's still gooey after a week, it probably won't cure; cut it out and start over with a fresh tube.

Common causes: the joint moves more than the caulk is rated for, the bead is too thin, the caulk shrank in a deep gap, or it's bonded to the back of the joint and can't stretch (three-sided adhesion). A rigid paint film over caulk can also crack as the joint moves. Match the product's movement rating to the joint, and use backer rod in deep gaps.

Sun, smoke, cooking grease, harsh cleaners, and tannins bleeding from wood can all discolor caulk over time, and some older or cheaper formulas yellow more than others. Painting over paintable caulk hides it. For silicone that has yellowed or stained, replacement is usually the only real fix.

Slice along both edges with a utility knife or razor, pull out as much as you can, then scrape the rest with a plastic scraper or a caulk-removal tool. A caulk softener helps with stubborn beads. Finish by cleaning the joint and wiping it with isopropyl alcohol. Details: Removing old caulk.

Scrape with a razor blade on glass and glazed tile, and a plastic scraper on acrylic or fiberglass tubs. Then use a silicone residue remover or mineral spirits (test on the finish first), and wipe with isopropyl alcohol until the rag comes away clean. New silicone won't stick to old silicone film.

If the mildew is only on the surface, a mildew cleaner or diluted bleach may lift it. If the black is under or inside the bead, it won't clean out; the caulk needs to come out, the joint needs to dry thoroughly, and a mildew-resistant silicone should go back in. Why it happens: Why shower caulk turns black.

You can cut back to sound caulk, clean the joint, and fill the gap with the same product, but the patch will usually show, and fresh silicone may not bond to the old bead. For wet areas, redoing the whole run is almost always worth it.

Replace it when it fails, not on a calendar. Look once a year for cracks, gaps, peeling edges, and discoloration that won't clean. Bathroom caulk usually needs attention sooner than interior trim caulk, and exterior sealants vary widely with sun exposure and product quality.

Latex caulk washes off with water while it's wet. For silicone and solvent-based products, wipe off as much as you can with a dry rag first, then use a hand cleaner made for sealants. On clothes, wash out latex before it dries; let silicone cure and peel or pick it off, because smearing wet silicone spreads it. Gloves prevent all of this.

Most household caulks are considered inert once fully cured. While curing, they give off vapors that range from mild to strong, so ventilate, wear gloves, and keep kids and pets away from wet caulk. Some polyurethanes contain isocyanates, which can cause respiratory sensitization. The product's safety data sheet (SDS) has the specifics.

In older buildings, yes. Some older caulks, glazing compounds, and putties contained asbestos, and the EPA has warned that caulk in some buildings built or renovated roughly between 1950 and 1979 may contain PCBs. If you're removing old caulk from an older building, especially lots of it, have it tested first and don't sand or grind it. More in Removing old caulk.

It's an acetoxy-cure silicone, which releases acetic acid (the same acid as vinegar) as it cures. The smell fades as the silicone cures. Acetoxy silicone can corrode some metals and etch or stain some natural stone and mirror backings, so choose a neutral-cure silicone for those. See RTV in the glossary.

Use a sturdy ladder on firm, level ground, keep three points of contact, don't overreach (move the ladder), and have someone spot you. On a roof, use fall protection, work in dry weather, and wear soft-soled shoes. Carry the gun on a hook or in a bag, not in your hand. Troy's full take is in the roof & gutters guide.

Only products specifically labeled for it. Many kitchen and bath silicones contain mildewcides that are harmful to fish, and ordinary caulks aren't rated for food contact. Look for "aquarium safe" or food-contact certifications on the label.

Only products rated for high temperatures, such as high-temperature silicone or refractory sealants. Ordinary caulk isn't made for that heat. Sealing pipe and cable penetrations in fire-rated walls is a different job that needs listed firestop products like 3M Fire Barrier CP 25WB+, installed to a tested system and your local code.

100% silicone rated for kitchen and bath. It handles standing water, cleaning chemicals, and the small movements of a sink rim. For undermount sinks, follow the sink maker's instructions; many specify silicone. More in the kitchen guide.

Yes. That change of plane moves slightly and catches water, so grout there tends to crack. Use silicone or a color-matched caulk made for kitchens, and keep the bead small and neat.

Many plumbers do, and some local codes require it, because it keeps mop water and worse from seeping under the base. A common practice is to caulk the front and sides and leave a small gap at the back so a leak shows up on the floor instead of rotting it unseen. Check your local code and follow your plumber's lead. See the bathroom guide.

Both, with different products. Outside, seal the joint between the window trim and the siding with an exterior sealant, but never block weep holes or drainage gaps at the bottom of the frame. Inside, a paintable caulk at the trim stops drafts. Zoe's full guide: windows & doors.

Weep holes in brick veneer and window frames, the bottom edges of lap siding, the overlap between siding boards, and drainage gaps at flashing. Those openings let water out. Sealing them traps moisture inside the wall, which is far worse than a draft.

If water is actively coming through, plug it with hydraulic cement first. For a dry, hairline-to-narrow crack, a polyurethane crack filler or injection kit works well. Cracks that are wide, keep growing, or have one side sticking out past the other are structural warnings; call a pro. More in the basement guide.

For horizontal joints and cracks wider than a hairline, press in backer rod and fill with a self-leveling polyurethane like Sikaflex Self-Leveling. It flows flat and handles traffic. Vertical joints get a non-sag product instead. More in the garage guide.

Clean the seam down to bare metal, let it dry, and apply a gutter sealant: butyl rubber or a tripolymer like Geocel 2300 Tripolymer both grip metal well. Work from inside the gutter so water flows over the seam, not into it. More in the roof & gutters guide.

It helps when it seals air gaps, because sound travels through any opening. In a soundproofed wall, acoustic sealant like OSI SC-175 Acoustical goes around the drywall perimeter, the plates, and electrical boxes. Caulking one outlet in an ordinary wall won't make a noticeable difference by itself. See the bedroom guide.

The top of the baseboard to the wall, yes: paintable caulk makes that line crisp. The bottom edge is a judgment call. On hardwood or floating floors, it's usually left uncaulked so the floor can move and the joint stays clean. In bathrooms or where mop water is a concern, a small bead of the right caulk can keep water out.

No. No brand pays us, sends us product for coverage, or approves what we write. The site is supported by Google ads, which we don't choose, and by Amazon affiliate links: if you buy a tube through one of our Amazon links, we may earn a small commission at no extra cost to you. Commissions never decide our picks. How we put reviews together is explained at the top of the reviews page.

The Crew: our house characters, each with a beat. Rosie runs kitchens, exteriors, and the Caulk Finder; Flavio handles wet zones; Karen does interiors and paint-ready finishes; Troy takes the roofs and heavy-duty jobs; Zoe covers windows, doors, and drafts. Meet them on the about page.

Because a good bead of caulk quietly keeps water out of walls, drafts out of bedrooms, and mold out of showers, and almost nobody explains how to choose or apply it. We are very serious about caulk. Someone has to be.

A short set of questions (where the joint is, whether it gets wet, whether you'll paint it, how much it moves) that points you to the right formulation and a tube to buy. Try the Caulk Finder.