Few things make a clean bathroom look grubby faster than old caulk. Over time, the flexible seal around a bathtub or shower can crack, peel, shrink or turn black with mildew. Worse, gaps can let water seep behind tiles or under the tub, where it can cause damage you won’t see until it’s expensive.
The fix is one of the most satisfying beginner DIY jobs around. It costs little, needs only basic tools and can be done over a weekend, mostly because the new caulk needs time to cure. Here’s how to do it.
What you’ll need
- A tube of 100% silicone or siliconised acrylic caulk labelled for kitchens and bathrooms, ideally with mould resistance.
- A caulking gun (unless your caulk comes in a squeeze tube).
- A plastic caulk-removal tool or a plastic scraper, plus a utility knife.
- Rubbing alcohol and clean cloths or paper towels.
- Painter’s tape.
- A caulk-smoothing tool, or simply a gloved fingertip.
- Disposable gloves and good ventilation.
Check the caulk tube for its recommended cure time before you start. Many bathroom caulks need around 24 hours before they can get wet, but this varies by product.
Step 1: Remove the old caulk completely
New caulk won’t stick well to old caulk, so it all has to go. Carefully slice along both edges of the old bead with a utility knife, keeping the blade low so you don’t scratch the tub or tiles. Then pull and scrape the old caulk out with a plastic tool.
Take your time. Stubborn bits may need a caulk-softening product, available at most hardware stores. Avoid metal scrapers on acrylic or fibreglass tubs, which scratch easily.
Step 2: Clean and dry the joint
This is the step most people rush, and it’s the one that matters most. Vacuum or wipe out loose debris, then clean the joint with rubbing alcohol to remove soap scum and residue.
If you see mildew, clean it according to the instructions on a bathroom mould cleaner, rinse and let everything dry thoroughly. Ideally, don’t use the shower for several hours beforehand. Caulk applied over damp surfaces may not bond properly.
Step 3: Tape both sides of the gap
For crisp, professional-looking lines, run painter’s tape along both sides of the joint, leaving a gap a little wider than the bead you want. This is optional, but it makes a big difference for beginners.
Tip: if you’re caulking around a bathtub, fill the tub with water first. The extra weight makes the tub settle slightly, so the caulk cures at the joint’s widest point and is less likely to crack later. Drain it after the caulk has cured.
Step 4: Apply a steady bead
Cut the tip of the caulk tube at a 45-degree angle, starting small. You can always cut more. Load the gun, then squeeze gently while moving along the joint at a steady pace, pushing the caulk into the gap.
Work in sections of about 60 to 90 centimetres (two to three feet) so the caulk doesn’t start to skin before you smooth it.
Step 5: Smooth and remove the tape
Run a smoothing tool or a gloved, slightly damp fingertip along the bead in one continuous motion. This presses the caulk into the joint and gives it a neat, concave finish. Wipe excess off your tool often.
Peel off the painter’s tape right away, pulling it away from the joint at an angle while the caulk is still wet.
Step 6: Let it cure
Leave the bathroom ventilated and keep water away from the new seal for the full cure time listed on the tube. Resist the urge to test it early.
Common mistakes to avoid
- Caulking over old caulk. It might look fine at first, but it will peel quickly.
- Skipping the cleaning step. Soap residue and moisture are the main reasons caulk fails.
- Too much caulk. A huge bead is harder to smooth and looks messy. A modest bead pushed into the gap works better.
- Using the wrong product. Make sure the label says it’s suitable for wet areas like baths and showers.
If you discover soft, crumbling grout, loose tiles or signs of water damage once the old caulk is out, that’s a bigger repair. It’s worth getting advice from a professional before sealing over it.
The wrap-up
Re-caulking a bathtub or shower is a small job with a big payoff: a cleaner look, a better seal and peace of mind. Remove every bit of the old stuff, clean thoroughly, apply a steady bead and give it time to cure. Your bathroom will look years younger by Monday.
Image: Old bathroom with subway tiles by Alf van Beem via Wikimedia Commons, CC0 1.0
