Reseal or re-waterproof? Fixing a leaking shower without a full reno

A shower has two lines of defence: the tiled surface on top and the waterproof membrane underneath. A reseal repairs the first; re-waterproofing replaces the second.

A reseal is the right fix when the membrane is still sound, and money wasted when it is not.

Firm tiles, damp that follows your showers and no failed reseals behind you point towards a reseal. Hollow tiles, damp along the whole wall and a reseal that did not last point towards the membrane.

A flood test with the surface sealed is what actually decides it.

Re-waterproofing usually means rebuilding the shower recess only, not renovating the whole bathroom.

Think of a tiled shower as a raincoat over a wetsuit. The tiles, grout and silicone are the raincoat: they shed nearly all the water, but not every drop. The membrane underneath is the wetsuit: a continuous waterproof layer across the floor and up the walls that catches whatever gets through and runs it to the drain. When a shower leaks, one of those layers has failed, or both have. A reseal renews the raincoat. Re-waterproofing replaces the wetsuit, and to reach it the raincoat has to come off first. Everything else in this guide follows from that.

Resealing deals with the surface. The old silicone is cut out of the corners and joints, tired grout is raked out and renewed, the joints are sealed, and fresh silicone goes where surfaces meet. That stops water getting in through the gaps that open up as grout ages and silicone lets go, and when the membrane below is still intact, it fixes the leak completely. What it cannot do is repair anything under the tiles. If the membrane has split at a corner or was never bonded to the waste, a reseal slows the water down for a while, and then the damp comes back.

Re-waterproofing means taking the shower back to its bones. The screen comes off, the wall and floor tiles in the shower are removed along with the bed under them, and the substrate is repaired where it has been damaged. The waste is reset, the corners and pipe openings are detailed, and a new membrane goes on in coats with time to cure. It is flood-tested, then screeded, tiled, grouted and sealed. It is a bigger job than a reseal, with the shower out of use for days rather than one, and it is the only fix for a membrane that has failed.

Some signs lean towards a reseal. The tiles are firm and sound solid when tapped. The damp next door gets worse on shower days and eases when the shower rests. The silicone is visibly split or lifting and the grout is cracked or missing. Nobody has resealed it before. Other signs lean towards the membrane. Several floor tiles sound hollow. The whole base of the wall behind is damp rather than one corner. White salts keep appearing on the grout. And the strongest sign of all: it was resealed recently, it helped for a season, and the damp is back. None of these is proof on its own, but together they tell you which way a test is likely to go.

Clues narrow it down; a test decides it. With the surface sealed, the floor waste is plugged, water is held in the shower base, and damp readings are taken on the far side of the wall and, where there is one, on the ceiling underneath. If the readings stay steady, the membrane is holding and the surface was the problem. If they climb with the surface sealed, the membrane is letting water through. Before any of that, it is worth ruling out the pipes with Sydney Water's meter test, because a leaking pipe in the wall looks like a leaking shower from the other side and is fixed in a completely different way.

You will see products and services that promise to waterproof a shower without lifting a tile. They are clear sealers applied to the grout and tiles, sometimes very good ones, and they do what a reseal does: make the surface better at shedding water. No sealer can rebuild a membrane that sits under tiles nobody has lifted. Over a sound membrane they can help. Over a failed one they buy a little time, and the leak continues underneath. Ask anyone selling one what happens if the membrane has already gone.

Not every leaking shower is a grout or membrane problem. The floor waste can leak where it meets the membrane or where it joins the pipe below, and that is fixed by lifting a small ring of tiles around the drain rather than the whole floor. A supply pipe, the mixer body or the shower arm can leak inside the wall, which is a plumbing repair reached from the front or the room behind. These are the reasons a proper test checks the pipes, the waste and the membrane separately rather than assuming.

A failed membrane does not mean a new bathroom. Usually only the shower recess is rebuilt, and the basin, the toilet and the floor outside the shower are left alone. A bathroom renovation that leaves every fixture in its original position is one of the cases where Building Commission NSW needs no Notice of Work. Two cautions apply. Asbestos is a possibility in any home from before the late 1980s, according to SafeWork NSW, so old wall linings get checked before stripping starts. And by Sydney Water's own guidance, a renovation is a job for a licensed plumber, not a weekend project.

Bubbling paint, swollen skirting, grout that never dries: how to read the signs of a leaking shower in the bathroom, next door, below and outside.