How do I apply silicone so it looks neat?

Silicone is judged entirely on the finish, and the finish is decided by the nozzle cut and by doing the tooling in one pass.

Safety

What you'll need

• A decent skeleton gun with a smooth trigger
• Sanitary-grade silicone for bathrooms and kitchens
• Masking tape and a tooling spatula

Step by step

1. Remove all the old sealant first.New silicone will not bond to old. Cut it out with a plastic blade, then clean the residue with a silicone remover — any film left behind causes the new bead to lift.
2. Clean and dry the joint completely.Methylated spirit or isopropyl alcohol, then let it dry. Silicone will not stick to soap residue, damp or dust.
3. Choose the right sealant.Sanitary-grade with a fungicide for bathrooms and kitchens. Frame sealant for windows. Painter's acrylic caulk for gaps you intend to paint — silicone cannot be painted.
4. Cut the nozzle at 45 degrees.And slightly narrower than the gap you are filling. A nozzle cut too large is the reason most beads are too fat and hard to tool.
5. Fill a bath before sealing it.Water in the bath, or stand in the shower tray. It loads the unit down so the joint is at its widest, and the seal then does not tear when it is used.
6. Mask both sides for the sharpest line.Tape parallel to the joint, leaving the gap plus a couple of millimetres. Pull it away while the silicone is still wet.
7. Keep the gun moving steadily.Constant trigger pressure and constant speed, pushing the nozzle ahead of the bead. Stopping mid-run leaves a lump you cannot tool out.
8. Do it in one continuous run.Plan the length so you can complete a side without stopping. Joins in a bead always show.
9. Tool it once, in one pass.A wet finger, a spatula or a soapy solution. One firm pass. Going back over silicone that has started to skin drags it and ruins the finish.
10. Release the trigger before lifting.Most guns have a release catch. Without it the silicone keeps extruding after you stop.
11. Let it cure fully before use.24 hours minimum, longer in cold or humid conditions. Using a shower early is how a new seal fails within weeks.

Tips

• Cut the nozzle smaller than you think. A fat bead is impossible to tool neatly.
• Fill the bath before sealing it, so the joint is at its widest under load.
• Tool once, in one pass. Going back over it is what makes silicone look amateur.

Common mistakes

• Applying new silicone over old — Silicone does not bond to cured silicone or to its residue. The new bead lifts within weeks, usually taking mould with it underneath.
• Sealing an empty bath — When the bath fills it drops on its supports and the joint opens, tearing the seal. Fill it first so the joint is sealed at its widest.

If it doesn't work

Questions people ask