Mouldy Caulk? Here's How to Replace It Yourself
That dark, cracked line of caulk around your bathtub or shower isn't just ugly — it's letting water seep behind the tiles, which can cause mould, rot, and structural damage over time. Re-caulking is one of the most impactful quick wins in home maintenance, and it costs less than £10 and a couple of hours of your time.
What You'll Need
- Stanley knife or caulk remover tool
- White spirit or isopropyl alcohol
- Masking tape
- Silicone sealant (bathroom-grade, mould-resistant)
- Caulk gun (or use a squeezable tube)
- Wet finger or caulk smoother tool
- Old towel or cloth
Step 1: Remove All the Old Caulk
Use a Stanley knife to score along both edges of the old caulk line, then a caulk remover tool (or the flat edge of the knife) to lift it away. Take your time — any caulk left behind will prevent the new sealant from bonding properly. Use a stiff brush or an old toothbrush to clean out any residue from the joint.
Step 2: Clean and Dry the Surface
Wipe down the joint with white spirit or isopropyl alcohol. This removes soap scum, grease, and any remaining residue. Then leave it to dry completely — at least an hour, ideally overnight. This is the most important step. New caulk applied to damp or dirty surfaces will peel within weeks.
Step 3: Apply Masking Tape
Run two strips of masking tape on either side of the joint, leaving a gap the width of the bead you want to apply. This gives you clean, straight edges and makes the job look professional even if it's your first time.
Step 4: Apply the Caulk
Load the silicone into the caulk gun and cut the nozzle at a 45-degree angle to give a fine, controlled bead. Apply steady, even pressure and move smoothly along the joint in one continuous motion. Don't stop and start — you want one unbroken line.
Step 5: Smooth the Bead
Wet your finger with a little water (or use a caulk smoother) and run it along the bead in a single smooth stroke to press it into the joint and give a neat, slightly concave finish. Do this before the caulk starts to skin over — usually within 5–10 minutes of application.
Step 6: Remove the Masking Tape
Peel away the masking tape immediately — while the caulk is still wet. Pull it back at 45 degrees, away from the caulk line. Leave the sealant to cure fully before getting it wet — check the manufacturer's instructions, typically 24–48 hours.
Tips for a Professional Finish
Always choose a bathroom-grade silicone with an anti-mould additive — standard decorators' caulk will go black within months in a wet environment. And never rush the drying time. The patience you put in at Steps 2 and 6 is the difference between caulk that lasts five years and caulk that peels in five months.