How do you redo mouldy silicone?

Silicone sealant replacement, step by step

These steps are general practical guidance rather than an official procedure. Plan the job for a time when nobody needs the shower until the new sealant has cured.

1. Let the area dry. Stop using the shower for a while so the joint and nearby tiles are dry when you start.
2. Cut away the old sealant. Run a sealant remover tool or a sharp blade along both edges of the old bead, then pull it out in strips.
3. Remove the residue. Scrape off the film and pieces left behind without scratching the tiles, glass or tray.
4. Clean and dry the joint. Wash out dirt and mould, rinse, then let the joint dry fully so the new sealant can grip.
5. Mask both edges. Run tape along each side of the joint, leaving a neat, even gap where the new bead will sit.
6. Apply one even bead. Squeeze the sealant into the gap in one steady, continuous line.
7. Smooth, peel and leave to cure. Smooth the bead, peel the tape off straight away while the sealant is still wet, then leave it to cure as its label says.

Why sealant turns black or leaks

HDB's guide to toilet fittings says shower screen sealant joints that turn yellowish or black, with water leaking through them, come from a build-up of dirt, fungi growth or the sealant losing its adhesion. HDB's solution is to clear dirt regularly and replace the old sealant with a suitable one. Its maintenance tips also say to replace the sealant or gasket when it is detached or torn.

In practice, if a mouldy silicone shower joint turns dark again soon after a thorough clean, the sealant needs replacing. For mould on the surrounding tiles and grout, see how to remove bathroom mould.

Choosing a sealant for a bathroom

This part is practical guidance. Choose a sealant whose label says it is made for bathrooms, kitchens or sanitary use, and that it resists mould. If you plan to reseal bathroom joints yourself, follow the label's own instructions for surface preparation, temperature and curing.

Resisting mould is not the same as stopping it for good, so the new joint still needs regular cleaning.

Curing time and leaks

Keep water off the new bead for as long as its label says before you use the shower. Until then, avoid touching or testing the joint.

A sealant bead only seals the joint between the tiles and the tray, bath or screen. HDB says ceiling leaks happen when water from the flat above seeps through the floor slab, usually from wear and tear of the waterproof membrane and screed. HDB adds that this is common in older buildings and typically occurs in toilets and bathrooms. A new bead does not repair the membrane or screed, so it does not fix a leak below.

If water is already marking the ceiling below, read our guide to a ceiling leak from upstairs first.

Keeping new sealant clean

HDB advises cleaning the glass and sealant to prevent fungi growth.

If you use a disinfectant, NEA says to prepare and apply it according to the manufacturer's guidelines, leave it on for the stated contact time and use the protective equipment its Safety Data Sheet prescribes. NEA names household bleach (sodium hypochlorite) as the most widely used disinfectant and lists hypochlorites as fungicidal. It recommends ventilating the home during and after cleaning, and cleaning bathrooms from high to low and from the shower towards the toilet bowl.

For more upkeep habits, see our post on bathroom maintenance to prevent leaks.

When to stop and call a professional

HDB says to engage a contractor to dismantle, alter or modify a tempered glass shower screen, and to replace worn-out parts. It also advises tightening brackets and hinges when they become loose. If you would rather not reseal the joint yourself, compare handymen.

Call a contractor if the joint keeps leaking after you reseal it, or if water reaches the flat below. Sealant work is not among the water service or sanitary plumbing works PUB describes, but if a contractor finds the water is coming from a pipe, repairing or replacing a concealed water pipe is PUB Licensed Plumber work.

For a leak that may involve pipes, compare plumbers and read about leak repair.

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