You’ve seen the ominous signs of aging caulk. First it was the brown tinge along the edges. Now its smooth and supple skin has turned brittle and cracked, opening the way for stubborn colonies of mildew to take hold, or for water to seep through and turn wallboard and framing mushy.
How to Caulk a Bathtub in 4 Steps
Whether it’s around your sink or between a bathtub and its tiles — moldy caulk has to go. Learn to re-caulk your tub and give it a fresh new seal in 4 easy steps.
1. Remove old caulk
Start by closing the pop-up drain in the tub and covering the entire tub with a drop cloth to protect it from scratches, residue, etc.
Take the razor blade and carefully pry the old caulking off the tub. Keep the angle of the blade as low as possible and watch the caulking to see if it’s being cut. If any of the caulking is left over on the tub, the new caulking won’t stick.
For this job, Tom sliced away the old acrylic latex caulk with quick, sharp strokes of a 5-in-1 painter's tool and a razor scraper. You can also use a utility knife to remove old caulking.
(Note: Metal blades can scratch plastic sinks, tubs, and surrounds; use a plastic razor blade instead. Caulk removers also harm plastic.)
2. Scrub caulk residue with soft rag
A dry, nonabrasive pad scours away every trace of caulk residue. (Clean up after silicone with a pad soaked in mineral spirits. But to avoid scratching plastic fixtures, use a soft rag dampened with mineral spirits, not a scouring pad.)
Wipe a damp cotton rag over the joint to remove the caulk dust and prepare the surface for the new caulk. Thoroughly dry the area with paper towels, a dry rag, or a hair dryer.
3. Tape off the wall
Lay parallel strips of blue painter's tape, about 3⁄8 inch apart, to keep the bead straight, uniform, and off surfaces where it shouldn't be.
Point the nozzle hole toward the joint; hold the gun equidistant from the surfaces on either side of the joint and about 45 degrees out from it.
Then apply steady pressure to the trigger as you move the gun smoothly along the entire length of the seam. Whether you push or pull the gun is a matter of personal preference.
Either way, keep the caulk gun moving at a steady speed matched to the rate that caulk is flowing out of the nozzle. Too fast, and the bead will be too thin, with bubbles or breaks in the seal; too slow, and you'll waste material and spend more time cleaning up.
4. Smooth out the caulk with a lint-free rag or paper towel
As soon as the seams are filled, dampen a lint-free rag or paper towel and press it into the joint with your finger. Pull it along the joint in one continuous motion to shape the fresh caulk into a concave bead.
Immediately remove the tape, one strip at a time, taking care not to let it touch any of the fresh caulk.
Then go back and smooth the bead again to eliminate the tiny ridges left by the tape. Let the caulking dry for 30 minutes before using the shower again. After that, the caulking will need 24 hours to cure, so don’t touch the caulking until then.
Bathroom Caulking: FAQs
Can I caulk over old caulk?
This Old House general contractor Tom Silva says no. “The key is to completely remove the old caulk, including the residue you can’t see,” he says. “You’ve got to start fresh with a clean, smooth, dry surface.”
By following Tom’s steps, “You should get five to ten years out of that seal, easy,” he says.
What kind of caulk do you use in the bathroom?
The best caulks for tubs, sinks, or shower stalls come in tubes labeled “Tub and Tile” or “Kitchen and Bath.” These are either acrylic latex or silicone compounds that have been chemically tweaked to resist mildew and to stick to smooth, nonporous surfaces. But they have distinctly different personalities.
Tenacious, waterproof, and very flexible, this type of caulk is also finicky about surface conditions, difficult to smooth, requires mineral spirits for cleanup, and emits a nose-wrinkling odor until cured.
It leaves a residue that’s hard for anything—including new silicone—to stick to. That’s why formerly siliconed surfaces should be scrubbed with an abrasive pad soaked in mineral spirits. Silicone caulk has a color palette limited to clear, white, and almond.
Compared with silicone, this kind of caulk is much more forgiving about the type and cleanliness of a surface it’s applied to. Smoothing it is easy, it cleans up with water, and it doesn’t have much if any smell.
While it does shrink more and dry harder than silicone—and will probably need to be replaced a little sooner—the replacement job should go faster. Acrylic latex caulk comes in a rainbow assortment of colors to match sink and tub glazes.
To remove any existing caulking, Tom advises using whichever tool is the most comfortable that has a flat enough blade to get behind the caulking without scratching it. These types of scrapers and blades can be found at home centers.
For caulking around a bathtub, Tom recommends using anything that is 100% silicone. In the segment, he used 100% Silicone Sealant in White, which is manufactured by Gorilla Glue.