Can I repair a cracked shower tray?

A shower tray does not crack because the material was bad. It cracks because it moved, and it moved because it was supported on legs or a partial bed instead of being carried evenly. That is why a repair applied without addressing the support fails within months, in the same place, and why the honest sequence is always: find out what is under it, fix that, then repair the crack.

Safety

What you'll need

• A two-part acrylic or gelcoat repair kit matched to the tray colour
• Wet-and-dry abrasive paper, 400 through 2000 grit
• Fibreglass matting and resin, for any crack that goes through
• Acetone or isopropyl alcohol for degreasing
• A rotary tool or a sharp knife for opening out the crack
• Polishing compound

Step by step

1. Find out whether the tray moves.Stand in it and shift your weight around, then kneel and press hard at the crack and at the centre. Any perceptible give, creak or movement means the tray is inadequately supported and no repair will hold. That is the job, not the crack.
2. Establish what kind of crack it is.Dry the tray completely and look at it under a torch held low. A fine surface crack in the gelcoat or acrylic skin, not passing through, is repairable. A crack that opens and closes as you press is structural. A crack radiating from the waste is nearly always the tray being tightened down onto an unsupported waste, and it will keep growing.
3. Deal with the support before the crack.If the tray moves, the only real repairs are to lift it and bed it properly, or to inject the void underneath with an expanding structural filler, or to replace it. Adjusting the legs is a stopgap that redistributes the flex rather than removing it.
4. Open the crack out.A filler laid over the surface of a crack has almost no bond area. Open the crack into a shallow V along its length with a rotary tool or the tip of a sharp knife, so the repair material has depth and flanks to grip. Extend slightly past each end of the visible crack — cracks run further than they show.
5. Reinforce from below if you can reach.Where a crack goes through and you have access underneath, that is where the strength comes from. Abrade the underside, degrease it, and lay two or three layers of fibreglass matting and resin over the crack, extending well past it. The visible repair on top is then cosmetic rather than structural.
6. Degrease properly.Soap, body oil and cleaning residue are all in that crack. Clean with detergent, rinse, dry, then wipe with acetone or isopropyl alcohol and let it flash off. This is the step that decides whether the repair sticks.
7. Fill in thin layers, slightly proud.Mix only what you can use in the pot life. Work the first layer well into the V, then build in layers rather than one thick one. Finish slightly proud of the surface — you are sanding it back, not trying to get it flush from the tube.
8. Cure fully, then sand back through the grades.Give it the full stated cure time, longer if the room is cold. Wet-sand at 400 to knock the proud material back level, then 800, 1200 and 2000, each at right angles to the last, then polish. Rushing the cure gives a repair that sinks and shows a line.
9. Reseal the tray junction and test properly.Cut out and replace the silicone at the tray-to-wall joint while you are there, since it will have been working against a moving tray. Then stand water in the tray for an hour with the waste plugged, and check underneath.
10. Know when to stop.A stone resin tray that has cracked through has cracked because it was bedded on a high spot or unsupported at that point, and repairs to it are cosmetic. A tray that has been repaired once and cracked again is telling you the same thing a second time. Replace it.

If it doesn't work