Fresh caulk keeps water out of the gap between your tub and the wall. Most of the job is prep: removing the old bead and letting everything dry.
The essentials
- Replace caulk that is cracked, peeling, stained or pulling away; gaps can let water into the wall and floor.
- Remove all of the old caulk, then clean and dry the joint completely before you apply anything new.
- Use a sealant labeled for kitchens and baths, and give it the full cure time on the label before the shower gets wet.
- Don’t caulk over mold. EPA advises scrubbing it off hard surfaces with detergent and water and fixing the moisture that feeds it.
The caulk around a bathtub has a hard life: hot water, cleaning products and constant movement as the tub fills and drains. When it cracks or turns black, it stops doing its real job, which is keeping water out of the gap where the tub meets the wall. Re-caulking is one of the most useful small jobs you can do in a bathroom.
Signs it’s time
- Cracks, gaps or sections that have pulled away from the tub or tile
- Dark spots that come back no matter how often you clean them
- Caulk that is crumbling, peeling or has gone hard
- Loose or soft grout or tile next to the tub, which can mean water is already getting behind it
If the wall behind the tub feels soft or the floor nearby is stained, call a professional before you re-caulk. Fresh sealant won’t fix water damage that is already in the wall.
Tools and materials
- A plastic caulk removal tool or utility knife, used carefully
- Caulk remover (optional, for stubborn silicone)
- Detergent, a scrub brush and clean rags
- Rubbing alcohol for a final wipe
- Painter’s tape
- A caulk gun and a tube of kitchen-and-bath sealant, ideally mildew-resistant
- A caulk smoothing tool, or a gloved fingertip
Step 1: Remove the old caulk
Cut along both edges of the old bead, then peel or scrape it away. A plastic tool is less likely to scratch acrylic or fiberglass tubs than a metal blade. For silicone that won’t budge, apply caulk remover and give it the time the label suggests.
Get every last bit out. New caulk sticks poorly to old caulk and soap scum, and leftovers make a lumpy line.
Step 2: Deal with mold and clean the joint
EPA’s advice for mold on hard surfaces is simple: scrub it off with detergent and water, then dry the area completely. EPA is also clear that you shouldn’t paint or caulk over moldy surfaces.
Finish by wiping the joint with rubbing alcohol on a clean rag to remove any remaining soap film.
Safety first
EPA suggests that a homeowner can usually handle a moldy area of less than about 10 square feet. If mold covers more than that, keeps coming back or is growing inside the wall, the problem is bigger than the caulk. Fix the source of the moisture and consider professional help.
Step 3: Let it dry
The joint has to be bone dry before you caulk. Run the bathroom fan, open a window if you can, and give it several hours or overnight. Caulk applied over a damp joint may not bond, and trapped moisture invites mold.
Step 4: Tape and apply the new bead
- Run painter’s tape along the tub and the wall, leaving a gap the width of the bead you want.
- Cut the tip of the tube small, at a 45-degree angle. You can always cut more off.
- Hold the gun at a steady angle and push a continuous bead into the joint, moving at an even pace. Work one side of the tub at a time.
Pro tip
Don’t stop in the middle of a long run if you can help it. Pausing leaves a blob, and restarting rarely matches. Release the trigger pressure just before the corner, then start the next side there.
Step 5: Smooth it and let it cure
Run a smoothing tool or a gloved fingertip along the bead to press it into the joint and leave a neat, slightly concave surface. Pull off the tape right away, while the caulk is still wet, pulling it away from the bead at a low angle.
Then leave it alone. Check the label for the cure time before anyone showers, and keep the room ventilated while it sets.
Help it stay clean longer
According to EPA, the key to mold control is moisture control. A few habits keep new caulk looking fresh:
- Run the bathroom fan during showers and for a while afterward.
- Squeegee or wipe down the tub and walls after use.
- Fix dripping faucets and leaks promptly.
- Keep indoor humidity below 60 percent, and ideally between 30 and 50 percent, as EPA recommends.
Make a quick check of the caulk part of your seasonal routine, along with the other jobs on our fall home maintenance checklist. If you’re repainting the bathroom while you’re at it, our paint sheen guide explains which finishes stand up to moisture.
Common questions
Should I use silicone or acrylic caulk?
100% silicone stays flexible and handles water well, but it can’t be painted and is trickier to smooth neatly. Siliconized acrylic is easier to tool and cleans up with water. Either can work if the label says it’s suitable for tubs and showers.
Can I put new caulk over the old caulk?
It’s better not to. New caulk doesn’t bond well to old caulk, and any mold or moisture underneath gets sealed in. Take the old bead out first.
How long before I can use the shower?
Check the label. Many kitchen-and-bath sealants need about a day before they get wet, and cool or humid conditions can stretch that.
Why do some people fill the tub with water before caulking?
A full tub settles slightly under the weight. Caulking it in that position means the bead isn’t stretched every time the tub is filled. If you try it, follow your tub and sealant manufacturers’ instructions.
This guide is general information, not professional advice. Follow the manufacturer’s instructions and your local building codes, and hire a licensed professional for electrical, gas, structural or roofing work.