Sealing Around a Shower Tray for a Watertight Finish

Why the Tray-to-Tile Joint Is the Weak Point

A shower tray takes a surprising amount of punishment. Every time somebody steps in, the tray flexes slightly underfoot, and every time the water runs, that joint between the tray rim and the bottom row of tiles is asked to move with it. If the sealant is too rigid, applied too thinly, or simply bridging a gap it was never meant to fill, it will crack within a season. Water then trickles behind the tiles, soaks into the substrate and eventually shows up as a stained ceiling downstairs or a soft, crumbling patch of plaster.

The good news is that sealing a shower tray properly is a genuinely straightforward DIY job. It needs the right silicone, a properly prepared gap, and about an hour of patience. Get those three things right and the seal will stay watertight for years rather than months.

Choosing the Right Silicone

Not all silicone is equal, and the cheap tube from the bargain bin is usually the one that goes black and peels within six months. Look for a sanitary silicone or a dedicated shower and bathroom sealant. These contain a fungicide to hold mould at bay, and they are formulated to stay flexible as the tray moves.

• Acetoxy cure silicones smell faintly of vinegar as they set. They bond well to ceramic tiles and most trays, and they are the traditional choice.
• Neutral cure silicones have almost no smell and are kinder to sensitive surfaces. Choose neutral cure if you have an acrylic tray, a natural stone surround or any plastic trim, as acetoxy can attack some of these over time.
• Avoid general-purpose builders' silicone, decorator's caulk (which is not waterproof) and rigid grout, which cannot accommodate movement.

Buy a decent brand and buy fresh. Silicone has a shelf life, and an old tube that has been in a cold garage will cure badly and skin over unevenly. One 310ml cartridge is normally plenty for a standard 1200mm tray.

Preparing the Joint Properly

This is where most seals fail, not at the point of application. Silicone will not stick to dust, soap residue, old sealant or damp surfaces, and no amount of technique will compensate.

• Strip out every trace of the old silicone using a silicone remover and a plastic scraper. Metal blades can scratch trays and tiles, so keep them away from the job.
• Wipe the joint down with methylated spirits or a dedicated silicone cleaner, then leave it to dry completely. Silicone needs a bone-dry surface.
• Check the gap. Ideally you want a joint of 3mm to 6mm between tray and tile. Anything wider than about 8mm should be filled first with a closed-cell backing rod, which gives the silicone something to grip and stops it sinking into the void.
• If the tray has any movement in it, sort that out before sealing. Bed it down, check it with a spirit level, and tighten the waste and any fixing brackets. Sealing a wobbly tray is a waste of a good tube of silicone.

One trick that pays off: fill the tray with water and leave it for an hour before you seal. This settles the tray into its loaded position, so the bead you apply is the bead that will actually be needed once somebody stands in it.

Applying the Bead

Run a strip of low-tack masking tape along the tile face and along the tray rim, leaving the joint exposed. It feels fussy, but it gives you a crisp, professional line and saves a lot of clean-up.

Cut the nozzle at roughly 45 degrees to a width that matches the joint, then run the bead in one continuous movement. Push the cartridge rather than pull it, keeping a steady angle and a constant speed. Squeeze gently and let the bead sit slightly proud of the joint rather than trying to spread it thin. Stopping and starting mid-run creates weak points, so work in a single pass from one end to the other, then repeat for the remaining sides.

Smoothing and Finishing

Smoothing is not just cosmetic. Pressing the silicone into the joint with a tool improves contact with both surfaces and forces out air pockets.

Use a silicone profiling tool, a plastic spatula or a clean finger dipped in a little washing-up liquid solution. Work along the joint in one steady stroke, keeping the tool at a consistent angle, and wipe it clean after every pass so you are not dragging old silicone back along the bead. Some installers prefer a dry finger or tool and a light mist of soapy water over the bead instead; either approach works, but be consistent along the whole length.

Peel off the masking tape while the silicone is still wet, pulling it away from the joint at a shallow angle. If you leave it until the silicone has skinned over, you will drag ragged edges with it.

Curing, Testing and Ongoing Care

Leave the seal alone for at least 24 hours, and ideally keep the shower out of use for 48 hours. Silicone cures by absorbing moisture from the air, and a cool, damp bathroom will slow that process. Running the shower early is the quickest way to ruin an otherwise perfect job.

Once cured, test it by running the shower for a few minutes and checking underneath the tray and along the ceiling below if you have access. A small weep now is easy to deal with. A hidden leak is not.

After that, treat the bead kindly. Squeegee the walls after use, leave the door or curtain open to ventilate, and clean with a mild bathroom cleaner rather than abrasive creams or neat bleach, both of which break down the silicone surface and encourage the mould you are trying to prevent. If a small area does lift or go black, cut it out cleanly, dry the joint and patch it with the same product. A well-applied seal, looked after, should give you five years or more of trouble-free showering.