How do I use a caulking gun neatly?

A neat bead of sealant looks like a skill and is mostly three decisions made before you start. Most bad results come from a nozzle cut too large and from stopping the gun before releasing the pressure.

Safety

Step by step

1. Prepare the joint first.Remove every trace of old sealant, clean the surfaces and let them dry completely. New sealant over old bonds to the old, and the whole lot lifts away later as a strip.
2. Mask both sides if you want a crisp line.Tape either side of the joint leaving the gap you want. It is an extra five minutes and it is how a first attempt looks like a tenth.
3. Cut the nozzle small.Start smaller than the gap and enlarge if needed — you cannot uncut it. Cut at about 45 degrees, which lets the nozzle lie along the joint and shapes the bead as it comes out.
4. Pierce the inner seal.Most tubes have a foil seal under the thread. Puncture it with the spike on the gun or a long screwdriver, or nothing will come out however hard you squeeze.
5. Hold the gun at the same angle as the cut.About 45 degrees to the joint, with the cut face flat against it. That is what makes the nozzle shape the bead rather than just deposit it.
6. Push, do not pull.Pushing the gun forces sealant into the joint ahead of the nozzle. Pulling drags it along the surface. Pushing is the single biggest difference between a bead that adheres and one that sits on top.
7. Move at a steady rate.Constant trigger pressure and constant speed, in one continuous movement where possible. Stopping and starting leaves lumps, and the joins are where beads fail.
8. Release the trigger before you stop.Sealant keeps extruding under residual pressure. Flip the release catch a moment before the end of the run, or the bead ends in a blob.
9. Tool the bead within two minutes.A wetted finger, a plastic shaping tool, or a wet sponge. Tooling presses the sealant into contact with both surfaces — an untooled bead often is not actually stuck.
10. Use soapy water rather than plain.A drop of washing-up liquid in water stops silicone dragging on your finger and gives a much smoother finish. Plain water works less well.
11. Pull the tape immediately.While the sealant is still wet, pulling away from the bead at a shallow angle. Left to skin over, the tape tears the edge off with it.
12. Fill deep gaps with backer rod first.A gap deeper than it is wide wastes sealant and cures badly. Foam backer rod sets the depth so the sealant bonds to two sides and can flex properly.

Tips

• Practise a run on a piece of card first. Two minutes of practice calibrates the trigger pressure and the speed.
• A dripless or smooth-rod gun costs a little more and reduces the after-run dramatically. Worth it if you do this more than once a year.
• Wipe the nozzle regularly during a long run. Accumulated sealant on the tip is what puts ridges in an otherwise clean bead.

Common mistakes

• Cutting the nozzle too big — It cannot be undone, and an oversized bead has to be tooled away rather than shaped. Start small and enlarge only if needed.
• Pulling the gun along the joint — It drags sealant across the surface instead of pressing it into the gap, so it looks acceptable and adheres poorly.

If it doesn't work

Questions people ask