01What a membrane does
02Which areas need it
03Where it sits in the order
04Curing and inspection
05Warning signs of failure
Waterproofing is stage 08 of 12 in a full bathroom renovation.
BATHROOM WATERPROOFING GUIDE FOR HOMEOWNERS
Waterproofing is the trade you never see once a bathroom is finished. It sits under the tiles, behind the screen and around the floor waste, and it decides whether the room is still sound years from now. This guide explains in plain language what the membrane does, where it goes, where it fits in a renovation and how to spot one that has stopped working.
Planning a wet area in Murrumbeena, Carnegie or Hughesdale? The Waterproofing service page covers how we handle this stage.
WHAT A WATERPROOFING MEMBRANE DOES
Reference photo: a finished shower recess with a floor drain. In a room like this, the membrane sits under the tiles and the floor falls to the waste. Stock image, not one of our projects.
Tiles and grout are not waterproof. Grout is porous, and water on a shower floor finds its way through hairline gaps, around the waste and along the line where wall meets floor.
The membrane is a continuous layer, either a liquid applied in coats or a sheet system, laid over the prepared substrate and beneath the tile bed. Its job is to catch that water and send it to the floor waste, instead of letting it reach timber framing, plasterboard, the slab or the room next door.
A membrane is only as good as its details. Corners and junctions are reinforced, the openings for mixers and shower arms are sealed, and the layer carries past the edge of the wet zone rather than stopping short.
WHICH AREAS NEED WATERPROOFING
The exact heights and extents come from Australian standards and building requirements, and these are updated from time to time. A renovation should follow the version that applies when the work is done, not whatever was done in the original bathroom.
Shower recess
The whole shower floor and its walls, with the junctions and floor waste fully detailed. This zone takes the most water.
Bathroom floor
The floor outside the shower is a wet area too. The membrane turns up the walls around the edge, so water on the floor can’t soak into the wall.
Bath and basin walls
Walls beside a bath and behind basins are protected where splashing is expected. How far the protection extends depends on the fixture and the layout.
Laundry
Laundry floors and the walls behind tubs are wet areas as well, which is why laundry renovations follow the same sequence.
Plumbing / Electrical
Pipes, mixer bodies and the floor waste go in first, so every opening already exists when the membrane is applied.
Waterproofing
The substrate is cleaned and primed, junctions and openings are detailed, and the membrane goes on in coats to the required thickness.
Tiling
Tiles only go down once the membrane has cured and been checked. Tiling too early hides any problems under the finished surface.
CURING AND INSPECTION BEFORE TILING
A liquid membrane needs time to cure before it is covered. The wait depends on the product, the number of coats, the temperature and the humidity, so the manufacturer’s instructions set it, not the tiler’s schedule. If it’s rushed, the film under the tile bed can end up soft, thin or damaged.
Before tiling, the membrane is checked for coverage, reinforced corners, sealed openings, the upturn at the walls and the fall to the waste. Some jobs also need the work documented before it is covered.
Ask to see the membrane before the tiles go on. After that, it’s hidden for good.
Reference photo: applying adhesive with a notched trowel, the tiling step that follows a cured membrane.
SIGNS A MEMBRANE HAS FAILED
Failed waterproofing often shows up outside the shower before it shows up inside it.
01Grout that stays dark long after a shower, or keeps cracking and crumbling.
02Hollow-sounding or loose tiles on the shower floor or hob.
03Mould or a musty smell that keeps coming back after cleaning.
04Swollen skirtings, architraves or door frames in the next room.
05Peeling paint, bubbling plaster or stains on the wall behind the shower.
06Silicone at the wall-floor joint that keeps splitting or lifting.
New grout can hide these signs for a while, but it rarely fixes the cause. If water is getting past the tiles, the layer underneath needs assessing. Our Leaking Shower Repairs page explains how a leak is traced. If the whole wet area needs rebuilding, see Shower Renovations.
SEEING THE SIGNS, OR PLANNING A NEW BATHROOM?
Whether you have a shower that’s leaking now or a bathroom you want waterproofed properly from the start, begin with an assessment of the room. Request a quote for homes in Murrumbeena, Oakleigh, Chadstone, Malvern East, Bentleigh East, Ormond and nearby suburbs, or contact us with a question first.