Regrouting
Silicone in a shower: what it does and why it fails
5 min read
Short answer
Silicone seals the junctions in a wet area that move: wall to floor, internal corners, around the waste and where tiles meet a bath or screen. It is a wearing part with a service life, not a permanent material, and it fails through movement, cleaning products, mould growing into it, or being applied over a surface that was not properly prepared.
Silicone is the least glamorous material in a bathroom and one of the most important. It is doing a job that grout cannot do, in the places where wet areas most often fail.
It is also the thing most commonly patched rather than replaced, which is why the same corner keeps going black.
Why junctions get silicone and not grout
Grout is cement-based and rigid. It is the right material for the joints between tiles across a flat field, where nothing much moves relative to anything else.
A junction is different. Where a wall meets a floor, or where two walls meet in a corner, two separate planes are moving independently: the building settles, materials expand and contract with temperature, and a shower base flexes slightly under the weight of somebody standing in it. A rigid material in a joint like that cracks, and a cracked joint at the bottom of a shower wall is a direct path for water.
Silicone is flexible, so it accommodates that movement instead of breaking. Grout in a wall-to-floor junction is one of the most common defects we find, and it is frequently what caused the leak.
What makes silicone fail
- Age and movement. Every cycle of expansion and contraction works the bead, and eventually it loses adhesion at one edge or splits down the middle.
- Mould growing into the material, which is what black staining that will not clean off usually is.
- Aggressive or repeated chemical cleaning, which degrades the surface over time.
- Poor preparation. Silicone applied over dust, soap residue, old sealant or a damp surface never bonds properly, and it can look fine for months before it lifts.
- The wrong product. Not every sealant is suited to a wet area, and a general-purpose one in a shower does not last.
- Too thin a bead, or one squeezed into a joint with no depth, which leaves nothing to flex.
Signs it needs replacing
- It has lifted away from the tile or the base along any part of its length.
- It has split, cracked or gone hard and brittle instead of staying rubbery.
- Black staining that returns within days of cleaning.
- It has pulled thin or gone see-through at a corner.
- You can slide a fingernail behind it anywhere.
Why new silicone cannot go over old
Silicone does not bond to cured silicone. A new bead run over an old one is held on by whatever it can grip at the edges, and it usually lets go within months. It also traps whatever was underneath, including any mould, and it hides the junction from view so nobody can see what is happening there.
The old bead has to be cut out completely, and the joint cleaned and dried before the new one goes in. That preparation is most of the work, and it is the part that decides whether the repair lasts.
What good work looks like
- The old sealant cut out in full, not skimmed or covered.
- The joint cleaned of dust, soap residue and old material, and dry before sealing.
- A sealant suited to wet areas, applied at a proper depth rather than a thin smear.
- Mould-affected areas treated during preparation instead of being sealed in.
- A stated curing time before the shower is used, because a bead loaded before it has cured through can lose adhesion at exactly the edge it was installed to protect.
In short
- Silicone seals the joints that move. Grout seals the ones that do not.
- Grout in a wall-to-floor junction is a defect, and a common cause of leaks.
- Silicone does not stick to cured silicone. The old bead has to come out.
- Black staining that returns within days is growth inside the material, not on it.
Common questions
- How often should shower silicone be replaced?
- There is no fixed interval. It depends on how heavily the shower is used, how well the room ventilates, what it is cleaned with and how well it was installed. Condition is the guide: silicone that has lifted, split, gone hard or stained through needs replacing whatever its age.
- Can I replace shower silicone myself?
- The application is straightforward. The preparation is where it goes wrong, because a bead that looks neat over a surface that was not fully cleaned and dried will lift within months, and cutting out old sealant without damaging the tile edge or the bath takes some care.
- Why does my silicone go black again so quickly after cleaning?
- Because the growth is inside the material rather than on it. Aged silicone develops micro-splits that hold moisture, and once growth is established in there a surface cleaner removes only the visible part. Replacing the bead is what resolves it.
Related service: Regrouting