Why does my shower tray creak and flex when I stand on it?

Acrylic and stone-resin trays are designed to be supported continuously across their base. Fitted on adjustable legs alone, or on five dabs of mortar, they behave like a drum — and a joint sealed to a moving surface has a very short life.

Safety

What you'll need

• A torch
• A spirit level
• Access to the tray's underside if there is a plinth

Step by step

1. Establish how much it actually moves.Stand in the middle and watch the silicone joint at the wall. Any visible opening or a creak means real movement, and that is enough to break a seal.
2. Look underneath if you can.Many trays have a removable plinth or an access panel. A torch underneath will show whether there is a full mortar bed, a few dabs, or only legs and fresh air.
3. Check the legs are all bearing.On a legged tray, every leg should be in firm contact with the floor. One that spins freely by hand is doing nothing, and the tray is spanning across it.
4. Check the floor itself.Press on the floor beside the tray. A springy timber floor under a heavy stone-resin tray will flex however well the tray is bedded, and needs noggins or a ply overlay first.
5. Look for the consequences already present.Cracked grout in the bottom row of tiles, a silicone bead that has parted at one end, or a dark line at the tray edge all say water has been getting in.
6. Adjust the legs only as a stopgap.Winding the legs down to take up the gap reduces the movement but does not create continuous support. It buys time; it is not the repair.
7. Understand the real repair.The tray comes out, the waste is disconnected, and it is relaid on a full bed of sand-and-cement mortar so it is supported over its whole base. That is what stops the movement permanently.
8. Check what is under the tray before resealing.If it has been moving for a while, expect damp chipboard or a wet joist. Resealing over a wet substrate seals the water in.
9. Reseal only once it is solid.Cut out the old bead, clean back to bare surfaces, and apply new sanitary silicone with the tray loaded — someone standing in it — so the joint is sealed at its widest.

Tips

• Seal a tray with weight in it. Sealing it empty means the joint is stretched every time someone steps in.
• Stone-resin and cast trays are heavy and stiff, but they still need full support — their weight makes an unsupported floor worse, not better.
• If the tray creaks and the ceiling below has any stain at all, treat it as an active leak, not a cosmetic issue.

Common mistakes

• Resealing a moving tray and expecting it to hold — Silicone stretches, but not through several millimetres of movement several times a day. The bead will part again within months and water goes underneath in the meantime.
• Packing under the tray with timber offcuts — Point supports concentrate load on an acrylic tray and crack it. Support has to be continuous, which means mortar, not packers.

If it doesn't work

Questions people ask