How to Replace Old Bath Sealant for a Clean, Watertight Finish

The thin line of sealant where your bath meets the tiles does more work than it looks. It keeps water from seeping behind the bath, where it can damage walls and floors without anyone noticing. Over time the bead cracks, shrinks away from the edge or grows dark with mould, and cleaning no longer helps. The fix is straightforward and inexpensive, and with a little patience you can get a result as neat as a professional's.

Check why it failed first

Before reaching for the sealant gun, have a quick look at the cause. Sealant often fails because a bath moves slightly when it is filled and emptied, because the joint was not clean when it was first applied or because it has simply reached the end of its life. If the gap is wider than a few millimetres, or tiles are loose or the wall behind feels soft, it is worth asking a qualified tradesperson to take a look before you seal over a bigger problem.

What you will need

• A sealant remover tool or a sharp craft knife
• Sanitary silicone sealant in a cartridge, in a colour that matches your fittings
• A sealant gun, unless you are using a squeezable tube
• A sealant smoothing tool, or a pair of disposable gloves
• Masking tape
• Washing-up liquid and water in a small bowl
• A suitable bathroom cleaner and a cloth
• Old rags or kitchen roll

Step 1: Remove the old sealant

Cut along both edges of the old bead with the remover tool, taking care not to scratch the bath or the tiles. Peel it away in strips, then use the tool or a plastic scraper to take off what remains. Be patient, because any left-over residue stops new sealant from sticking. A bottle of sealant remover gel can help soften stubborn silicone, and you should follow the instructions on the label.

Step 2: Clean and dry

Scrub the joint with a suitable cleaner to remove soap scum and mould, and wipe it clean. Then comes the most important part: let the joint dry completely. Leave the room well ventilated, and if you can, wait a day. Sealant will not hold properly on a damp surface, and trapped moisture can encourage mould to return.

Step 3: Mask the joint and fill the bath

Press masking tape in a straight line along the tile and along the bath, leaving a gap of around three to five millimetres for the sealant. Many people fill the bath with water before sealing, because the weight of the water makes the bath settle into its lowest position. If you seal with the bath empty, the bead may be stretched or split when the bath is used.

Step 4: Apply and smooth the bead

Cut the nozzle at an angle to give a small opening, narrower than the gap. Squeeze the trigger gently and move steadily along the joint in a single continuous line, pushing the sealant into the gap. Try to avoid stopping halfway along a side.

Smooth the bead straight away. Dip your smoothing tool or gloved finger into soapy water and draw it along the joint with light, even pressure, wiping the tool clean as you go. Peel off the masking tape before the surface skins over, pulling it away at a shallow angle.

Step 5: Let it cure

The cartridge will tell you how long the sealant needs before it can get wet, and this is often 24 hours or more. Keep the room ventilated, and do not be tempted to use the bath early. A rushed job usually fails sooner.

Keeping it looking good

Wipe the bath edge dry after use where you can, and keep the room ventilated to cut down on condensation. A gentle wash with mild cleaner stops mould taking hold. If you also notice small holes or cracks in the wall around the bathroom, our guide to filling and repairing small holes in a plastered wall will help with the neighbouring repair.

Frequently asked questions

Can I put new sealant over the old? It is not recommended. New sealant does not bond well to old silicone, so removing the old bead is worth the effort.

Which sealant should I choose? Look for a product labelled as sanitary or bathroom sealant, since these are designed for damp areas.

Why has my new sealant gone mouldy so soon? Usually because the joint was damp when sealed, or because the room stays humid. Better ventilation and thorough drying beforehand make a real difference.