How to reseal silicone around a bath or shower

What you need

• Silicone remover gel and a plastic scraper or Stanley knife
• Gloves and eye protection — remover gels are caustic or strong-solvent, and methylated spirits is flammable, so keep the window open and the fan on
• Neutral-cure sanitary silicone (mould resistant) — not acetic cure on stone
• Caulking gun, masking tape, methylated spirits
• Paper towel and a small container of soapy water

Step by step

1. Cut the old bead out completely

   Score both edges with a sharp blade and peel the bead away in one piece if you can. Then use silicone remover gel on the residue and scrape it back. New silicone will not stick to old silicone, so anything left behind becomes a leak path.

2. Degrease and dry

   Wipe the joint with methylated spirits and let it dry fully. Any soap film, mould spray residue or moisture stops adhesion. If the joint has been wet, give it a few hours.

3. Mask both sides

   Run masking tape along both sides of the joint, leaving between the two tapes exactly the width you want the finished bead to be. This is what separates a professional-looking bead from an obvious DIY one.

4. Lay the bead in one pass

   Cut the nozzle at 45 degrees, opening slightly smaller than the joint. Push — do not pull — the gun along the joint at steady pressure, finishing the full run in one movement if possible.

5. Tool it, then pull the tape immediately

   Dip a finger in soapy water and draw it along the bead once, firmly. Pull the masking tape off straight away while the silicone is wet, at a shallow angle away from the joint. Waiting until it skins ruins the edge.

6. Leave it alone for 24 hours

   No showers, no water on the joint. Neutral-cure silicone needs a full day. Using the shower that night is the most common reason a fresh bead fails within a month.

If the mould keeps coming back, the silicone is not the problem

Silicone that has been correctly applied to a dry, clean, sound surface does not repeatedly go black in the same spot within a few months. When it does, one of three things is happening, and none of them are fixed by another tube.

The joint is being fed water from behind. The most common cause. Water getting past a failed membrane, or through an unsealed penetration, sits behind the joint and the mould grows on the inside face where you cannot clean it. Read the waterproofing signs before you buy more silicone.

The room does not dry. A bathroom with no fan, or a fan that vents into the roof cavity rather than outside, stays damp for hours after every shower. Mould does not need a leak when it has that.

It was applied over the old bead, or onto a damp surface. Silicone will not bond to silicone, and it will not bond to a wet joint. Either way it lifts at the edges and the gap behind becomes exactly the environment mould wants.

Get all of the old silicone out. All of it.

This is where the job is won or lost, and it is the part everyone rushes. New silicone bonds to tile, acrylic, stone and glass. It does not bond to old silicone. Any residue you leave is a strip of joint that is not actually sealed.

Slice both edges with a sharp blade held flat against the surface, then peel the bead out in one piece if you can. What is left behind is a thin film that you can feel with a fingernail even when you cannot see it — that is the bit that matters. A plastic scraper takes most of it; a silicone remover gel softens the rest if it is stubborn.

Do not use a steel blade on an acrylic bath or shower base. It scratches, the scratches hold dirt, and you will look at them every day for the next decade.

Clean, then dry properly — this is not optional

Wipe the joint out with methylated spirits to remove soap film and any remaining silicone oils, and let it dry completely. In a warm room that is under an hour.

In a Melbourne bathroom in winter, it is not. An unheated internal bathroom in July can hold damp in a joint for a long time, and silicone applied over it will fail early and grow mould from inside. If you can do this job on a dry day with the window open, do. If not, leave the fan running for a couple of hours first, and do not shower in there the night before.

Choose the right silicone, and check one word on the tube

You want a neutral-cure silicone rated for wet areas and containing a fungicide — sold as bathroom, sanitary or mould-resistant silicone.

The distinction that matters: acetic cure (the type that smells strongly of vinegar) is fine on glazed tile and glass but can etch natural stone and corrode some metal fittings. If you have marble, travertine or any honed stone anywhere near the joint, neutral cure is the only safe answer. It costs a couple of dollars more.

Colour: match the grout, not the tile. A white bead against off-white grout reads as a repair from across the room.

Applying it: masking tape is the whole trick

Run painter's tape along both sides of the joint, leaving the gap you want the finished bead to be. Cut the nozzle at 45 degrees and no bigger than the joint needs — you can always trim more off, and an oversized nozzle is why beads end up three times wider than intended.

Lay the bead in one continuous pull if you can manage it, pushing slightly ahead of the nozzle rather than dragging behind. Stopping and starting is where air pockets get in.

Tool it immediately with a wet finger or a silicone tool — a light single pass, not repeated smoothing. Then pull the tape off straight away, while the silicone is still wet, at a shallow angle away from the joint. Waiting until it skins gives you a torn edge and defeats the point of taping.

Curing, and the bit that ruins good work

Silicone skins in about half an hour and cures fully in around 24 hours, longer when it is cold or the bead is thick. Do not use the shower during that window. A joint that gets wet while curing goes cloudy, bonds poorly, and starts the mould cycle immediately — which is how people end up believing the silicone itself was faulty.

Cheap trick worth knowing: fill the bath with water before you silicone around it, and let it out after the silicone has cured. A bath under load sits lower than an empty one, and a bead applied to an empty bath can tear the first time someone gets in.

Common mistakes

• Siliconing over old silicone
• Using acetic-cure (vinegar smell) silicone on natural stone — it etches it
• Cutting the nozzle too big and trying to tool away the excess
• Leaving the masking tape on until the silicone skins
• Getting the joint wet before it has cured

Questions people ask

Can I just put new silicone over the old?

No — silicone does not bond to silicone. It will look fine for a fortnight and then lift along one edge, and the gap behind is a better mould habitat than the joint you started with.

Why did my new silicone go mouldy in two months?

Almost always one of: the surface was damp when it went on, old silicone residue was left behind, or water is reaching the joint from behind. The third is the serious one.

Bathroom silicone or roof-and-gutter silicone?

Bathroom. Wet-area silicone contains a fungicide, which is precisely what you are paying for. General-purpose silicone in a shower will go black much faster.

How often should it be redone?

Every few years is normal in a shower that gets daily use. If yours needs it annually, something else is wrong — start with the exhaust fan.

Is resealing legal to do myself in Victoria?

Yes, this is not plumbing work. Note that Victoria — unlike Western Australia, whose homeowner list circulates widely online — publishes no official DIY plumbing exemptions at all. Sealing a joint is not plumbing; disconnecting a tap to do it would be.

This guide is general information, not advice for your particular house. Rules change — check the current position with the Building and Plumbing Commission, Energy Safe Victoria and WorkSafe Victoria before you rely on it. Plumbing, gas and electrical work must be done by a licensed practitioner. If your home was built or last renovated before 1990, assume asbestos until it is ruled out — see what a strip-out finds.