How do I get a neat silicone bead?

The common experience is a bead that looked acceptable coming out of the gun and turned into a smeared mess during smoothing. That is almost always because it was tooled more than once, or tooled too late. Silicone begins to skin within minutes, and every pass after the first drags the skin rather than shaping the bead.

Step by step

1. Remove the old sealant completely and degrease the joint.New silicone will not stick to old silicone residue, and the invisible film is what causes failure. GuideHQ has a guide on removing it properly. The joint must be dry as well as clean.
2. Cut the nozzle at an angle, slightly smaller than you think.Cut at roughly forty-five degrees, starting narrow — you can always cut more off. An over-large opening delivers more sealant than the joint can hold and the excess has to go somewhere, usually onto the tiles.
3. Mask both sides if you want a guaranteed clean line.Tape either side of the joint, leaving the gap you want the bead to be. It costs a few minutes and removes almost all the difficulty. The tape comes off immediately after tooling, never after skinning.
4. Push the bead rather than pulling it.Holding the gun so the nozzle pushes into the joint ahead of the sealant forces material into the gap. Pulling tends to lay it on the surface, where it looks fine and is bonded to very little.
5. Move steadily and do not stop mid-run.A consistent speed with consistent trigger pressure gives a consistent bead. Stopping leaves a lump; hesitating leaves a thin spot. Plan the run so you can do it in one movement.
6. Tool it once, in one direction, immediately.A wetted finger, a shaped tool or a rounded plastic edge — whichever you choose, do the whole run in a single pass and do not go back over it. This is the rule that decides whether the job looks professional.
7. Remove the masking tape straight away, pulling away from the bead.While the sealant is still wet. Leaving tape until the surface skins tears the edge of the bead and undoes the tooling.
8. Leave it alone to cure for as long as the tube says.Particularly in a bathroom. Using a shower before the sealant has cured is a very common reason a new bead fails early.

Tips

• Use a little soapy water rather than plain water for tooling. It stops the silicone dragging on the finger or tool.
• Cut the nozzle so the opening matches the joint. Most poor beads are simply too much material for the gap.
• For a bath, fill it with water before sealing and leave it full until the sealant cures, so the joint is at its widest when it sets.

Common mistakes

• Going back over the bead to improve it. — The surface has begun to skin. Each additional pass drags that skin and makes the finish worse, which is why beads deteriorate the more they are fussed over.
• Cutting the nozzle far too wide. — It delivers more sealant than the joint can take, and the excess ends up smeared across the surrounding surface.
• Sealing a joint that is still damp. — Silicone will not bond to a wet surface. It looks fine and peels away weeks later.

Questions people ask