Part of the guide: The Construction Defect Field Guide: 40 Defects by Trade, With Photos
Ask any inspector which wet-room defect they find most often and they will say sealant. Ask which one causes the most expensive damage and they will say the same thing. The two answers are connected by a misunderstanding: sealant at a shower tray is almost never the defect. It is the first component to give up when something underneath it moves, and if the report only says "re-seal", the next inspector finds the same crack in the same place, with a stained ceiling underneath it.
What does shower sealant failure look like?
Four presentations, in increasing order of concern:
- A hairline along the top or bottom edge of the bead where it meets the tile or the tray. The bead has pulled away from one surface. Common in the first months as the building dries.
- A crack across the bead, usually at a corner or where the tray meets a wall return. The junction has moved more than the sealant could stretch.
- The bead peeling off in a strip, often with black mould on the back of it. Water has been behind the sealant long enough to break its adhesion completely.
- Staining or a soft patch on the ceiling below the shower, sometimes with no visible sealant defect at all, because the water is going in at the back of the tray where you cannot see it.
The fourth is the one that matters, and it is the reason every shower tray inspection includes a look at the room underneath.
Why does sealant fail at the shower tray?
Three causes account for nearly all of it, and they are all installation, not product.
The tray moves. A shower tray should be bedded on a solid mortar or adhesive bed, or on a manufacturer's adjustable frame that has been packed to the floor. Trays sat on a few blobs of adhesive, on legs that were never levelled, or straight onto a timber floor that deflects, move when a person stands in them. A few millimetres is enough. The sealant is stretched with every shower and cracks in weeks. No sealant on the market survives a tray that flexes; the fix is under the tray, not on top of it.
The bead was sealed empty. Sealant applied while the tray was unloaded sets at the unloaded position; the first time someone stands in it, the junction closes and the bead is compressed, then opens again when they step out. Trays should be sealed with weight in them (a full bucket of water is the usual trick), so the bead sets at the working position. It takes a minute, and it is skipped constantly.
The upstand is missing. Most trays have, or can take, an upstand: a lip that sits behind the tiles so that water running down the wall lands inside the tray even if the sealant fails. Where the tiling was finished to the tray edge without one, the sealant is the only defence, and it will not be enough. This is the version that stains the ceiling with no visible defect above, because the water goes down the back of the tray.
Less often: the wrong product (an acrylic or decorator's caulk where a sanitary silicone was needed), sealant applied to a dusty or damp junction so it never bonded, or a wall-to-tray gap so wide that the sealant was bridging rather than sealing. All three show up as early peeling rather than cracking.
Is it a snag or a serious defect?
It depends entirely on the cause, which is why the report has to name it. A bad first bead on a rigid, upstand-fitted tray is a low-severity snag: rake out and re-seal, done in an hour. A cracked bead on a tray that moves is a high-severity defect, because it is an active water path into the floor structure and the room below, and the re-seal that the contractor will offer does not fix it. A stained ceiling under a shower is high regardless of what the sealant looks like, and the item needs to say that the source has to be found before the ceiling is patched.
The defect field guide lists this as item 24, and the neighbouring item: no fall to the drain in a wet room, as the other tray-level defect that sealant gets blamed for.
How do you report it?
The item needs four things the contractor cannot argue with: where it is, what was observed, whether the tray moves, and what is below it. The example in the box at the end of this article is the full line; the shape is:
- Location: room, and which junction (tray to wall, tray to floor, corner, door threshold).
- Observation: the presentation from the list above, with a length ("cracked along approx. 400 mm of the back wall junction") and whether there is mould behind the bead.
- Movement test: "tray deflects visibly when stood on" or "tray solid underfoot". This one sentence is what decides the fix, and it is the one most reports leave out.
- The room below: "ceiling below shower inspected: no staining" is a finding worth recording, because it dates the damage if a stain appears later.
- Action: for a rigid tray, re-seal with the tray loaded. For a moving tray, lift, re-bed and re-seal. For a missing upstand where water is already getting behind, the honest recommendation is to remove the bottom course of tiles and fit one; anything else is a re-seal every six months.
Two photographs: the whole junction from the shower door, so the room is recognisable, and a close-up with a card or probe in the gap so its size is visible. If the ceiling below is stained, a third of the ceiling with a door or light fitting in frame for location.
How to check a tray in two minutes
- Stand in the tray, near the drain, and shift your weight. Watch the junction with the wall. Any visible movement is a fail.
- Run a fingernail or a plastic card along the bead where it meets the tile and where it meets the tray. It should not lift or slide in anywhere.
- Look at the corners: they crack first.
- Run the shower for a minute onto the back wall and watch where the water goes at the junction. On a pre-completion inspection this is the only time you will see the tray under real conditions.
- Go downstairs and look at the ceiling directly below, in raking light from the window. Photograph it even if it is clean.
This sits in the wet-room section of the site inspection checklist; if you inspect for a living, the home inspectors' page shows how the photographs and the movement note go straight into the report from the bathroom floor.
What the fix should be, and what it should not be
Should be: the cause, then the sealant. A tray that moves is lifted and bedded solid. A missing upstand is fitted, or a proprietary seal strip installed behind the bottom course of tiles as the lesser remedy. Then the junction is cleaned back to bare, dry surfaces and sealed with a sanitary-grade silicone, tooled once, with the tray loaded, and left to cure before the shower is used.
Should not be: a second bead over the first. Sealant over sealant does not bond and traps the water that is already there. Nor should it be "monitor": a cracked tray junction does not improve, and a stained ceiling is what monitoring produces.
The re-inspection is where this item earns its place on the list. Stand in the tray again, watch the junction again, and photograph the ceiling below again. If all three are unchanged after a month of use, close it. If the new bead has cracked in the same place, the report was right the first time and the contractor did the wrong fix; that is now a paper trail rather than an argument.
Questions people ask
Can I just re-seal a shower tray?
You can, and if the tray is solidly bedded and the gap was simply a bad first bead, it will hold. If the tray moves when it is stood on, the new bead will crack in the same place within weeks, because the sealant is being asked to stretch every time someone showers. Check the movement first; it is a thirty-second test.
How long should shower sealant last?
A properly applied sanitary silicone on a rigid junction should last five to ten years before it discolours enough to replace. Sealant that fails within the first year of a new home has failed for a reason other than age, and the report should say so.
Why does new sealant go mouldy so fast?
Either it is not a sanitary-grade silicone with a fungicide, or it was applied over a surface that was already damp, or there is water sitting behind it. Black spotting inside the first few months is a symptom to record, not the defect itself: the defect is the moisture that is feeding it.
Who is responsible for a leaking shower in a new build?
The builder, for the length of the defects period (two years on most UK new homes, and the equivalent warranty period elsewhere), provided it is reported in writing with photographs and a date. A snagging report is that report. When to book one and what it costs covers the timing.