A shower tray that moves: sealant will not hold it still

What the joint is for

Sanitary silicone is an elastic seal. It follows small movement between tray and tile. It is not a structural adhesive, not packing for a hollow support, and not a way to lock a rocking tray in place.

A thicker bead does not change that. Elastic sealant has a limited amount of stretch. If the tray lifts and drops by millimetres every time someone stands in it, the joint is overloaded. It then tears through the middle (cohesion) or lets go of the tile or the tray edge (adhesion).

When to reseal — and when not to

Reseal when the tray itself is firm and only the old silicone is tired, stained or mouldy.

Do not reseal yet when the tray springs, creaks or sags as you step in. Repeating the joint while the support still moves is wasted work: the new bead fails the same way.

How to check

Stand in the empty tray, then with your weight where you normally stand under the shower. Watch the line between tray and wall. If that gap opens and closes, or you feel flex underfoot, the problem is the support — not a missing millimetre of silicone.

How that support is built (adjustable feet, a mortar bed, a board, packing, or something else) depends on that tray’s installation instructions. There is no single method that fits every acrylic, steel or ceramic tray. Follow the maker of the tray, not a universal “fill it with foam” recipe.

After the tray is stable

Only then treat it as a normal shower joint:

1. Cut out the old sealant fully and clean the flanks.
2. Degrease with a technical cleaner and let the faces dry.
3. Use primer only if that substrate needs it.
4. If the joint is deep, set closed-cell PE backer rod so the sealant bonds on two faces, not three.
5. Apply sanitary silicone and tool it so water can run off.

Exceptions

Old silicone on a tray that does not move is a joint replacement. A moving tray is a support job first. Do not mix the two.

If water is already behind the tiling, sealing the visible line will not dry that cavity. The leak path has to be understood before you close it again.