How do I seal a bathroom joint so it lasts?

The joint has to be completely free of the old silicone, and completely dry, before the new bead goes on. Nothing bonds to silicone residue — including new silicone — and that is the single reason most reseals fail within a year.

Removing the old bead

Cut it out with a sharp blade, then remove the film that is left. Dedicated silicone removers exist for this; a solvent wipe afterwards takes the oil that a blade cannot. This is the slow half of the job and it decides the result.

Choosing the cartridge

Sanitary grade, which carries a fungicide intended for permanently damp joints. Ordinary construction silicone in a shower goes black at the edges within a season, and the growth is inside the bead where no cleaner reaches.

Then the chemistry: acetoxy (smells of vinegar, cures fast, can stain natural stone and corrode some metals) or neutral cure (costs more, and is what marble, mirror backs and some coatings need).

Applying it

One continuous bead, tooled once within the skin time the maker states. Going back over a bead that has started to skin is what leaves the ridged finish people associate with a bad job.

Curing

Leave it for the full cure the manufacturer states before the shower is used, which is usually considerably longer than the skin time.

This does not replace the manufacturer's own instructions. Every dimension, thread size, flow rate, operating pressure, water seal depth and load figure on this page is reported from the manufacturer's own documentation, with its unit written as published, and named as such — none of it is measured here. A flow rate is reported with the pressure the manufacturer measured it at, and is never converted to another pressure, because no conversion exists.