How to Apply Bathroom Sealant

Black mouldy sealant around your bath or shower is unsightly and unhygienic. Replacing it is a 30-minute job that makes a bathroom look instantly fresher. The secret to a professional finish is all in the preparation and technique.

Tools and Materials

Silicone sealant (anti-mould, sanitary grade — Dow Corning 785 or UniBond is excellent), caulking gun, Stanley knife or sealant remover tool, masking tape, methylated spirits or white vinegar, kitchen roll, and a cup of soapy water with a spatula or your finger.

Step 1: Remove the Old Sealant

This is the most important step. Cut along both edges of the old sealant with a sharp Stanley knife. Pull it away in strips. Use a sealant remover tool to scrape any residue. For stubborn bits, apply sealant remover gel (leave 2 hours, then scrape). The surfaces must be completely clean and dry before applying new sealant.

Step 2: Clean and Dry

Wipe both surfaces with methylated spirits to remove grease and soap residue. Let it dry completely — 30 minutes minimum. Silicone will not adhere properly to damp or dirty surfaces. This step is what separates a lasting seal from one that peels off in 6 months.

Step 3: Mask the Edges

Apply masking tape along both sides of where the sealant will go, leaving a consistent gap (about 5-8mm). This gives you perfectly straight edges. Press the tape down firmly so sealant cannot bleed underneath.

Step 4: Apply Sealant

Cut the nozzle at 45 degrees to give a bead the right width for your gap. Apply steady pressure on the caulking gun and draw a continuous bead along the joint in one smooth motion. Do not stop and start — this creates bumps. Better to go slightly too much than too little.

Step 5: Smooth and Remove Tape

Dip your finger in soapy water and run it along the sealant in one smooth motion to create a concave profile. Only do one pass — going back and forth creates a mess. Immediately peel off the masking tape at a 45 degree angle while the sealant is still wet. Leave for 24 hours before using the bath or shower.

Preventing Mould

Use anti-mould sealant (contains fungicide). Keep the bathroom ventilated — run the extractor fan for 20 minutes after showering. Wipe down sealant weekly with bathroom spray. If mould appears on the surface, spray with bleach solution before it penetrates into the sealant.