By Mike Collins · 6 September 2026
Mike Collins · Instructor, The Plumbing School · 6 September 2026
Ask anyone on our 5-Day Bathroom Fitting Course which skill surprised them most and they usually say the same thing: silicone. It looks easy. It is, but only once you stop making the five mistakes below — the same five I end up fixing on jobs week after week.
If the old sealant is black with mould, laying new beads over the top is painting over rust. The mould keeps living underneath and the fresh bead peels within months. Cut ALL the old sealant out, clean the joint with a suitable cleaner, let it dry fully, then re-seal. Slow is fast here.
Not all “bathroom silicone” is equal. Around showers, baths and wet zones you want a quality, mould-resistant sanitary sealant — and critically, an appropriate type for the surface. On acrylic baths and shower trays, use a neutral-cure product designed for them; aggressive solvent-based ones can attack the surface. Read the tube. It matters.
A classic. Acrylic baths and trays flex when you stand in them. If you seal them empty, the first proper bath stretches the joint and splits the bead. Fill the bath (or tray) with water before you seal, seal it full, and let it cure before you drain it. The joint is then formed in its working position.
The crisp finish comes from a lightly dampened finger (or a proper tooling tool) drawn along the bead in one confident pass — not from mauling the joint for five minutes. Use masking tape on both sides for dead-straight lines on long runs, tool the bead, then pull the tape off immediately before the skin forms.
The most expensive one. If water is coming through the ceiling below, no amount of fresh silicone fixes it — it just hides the evidence for a month. Find the source (waste connections, tray edges, tile joints), make the repair, then seal. On the course we deliberately show you the failure points so you recognise them in your own bathroom.
Keep a roll of kitchen towel and a pot of soapy water with you. Wipe your tooling finger between every pass. The difference between a DIY-looking seal and a professional one is about 30 seconds of wiping per metre.
Sealing is a proper module on the 5-Day Bathroom Fitting Course — you’ll do it on a real installation in our training bays, not a demo video. If your bathroom’s on the list for next year, come and learn it properly: courses and prices here, or just message me.
