Short answer
AS 3740 is the Australian Standard for waterproofing domestic wet areas such as showers, bathrooms and laundries. It sets out where a waterproof membrane is needed, how it must be detailed at corners, joints, drains and pipe penetrations, and how floors should fall to the waste. The tiles and grout are not the waterproofing; the membrane underneath them is.
Tiles and grout are not waterproof
Grout and most tiles let small amounts of water through over time. What keeps water out of the walls and floor is a waterproofing membrane applied under the tiles. If that membrane is missing, thin, or badly detailed at the joints, the leak often shows up months or years later, well away from the shower itself.
What a properly waterproofed shower includes
- A membrane system suited to the substrate, applied at the thickness and number of coats the manufacturer specifies.
- Bond breakers at wall-to-floor and wall-to-wall junctions, so normal building movement does not tear the membrane.
- Upturns where the membrane turns up the walls, and waterproofing continued up the shower walls.
- A waste flange or puddle flange at the floor drain, sealed into the membrane.
- Sealed penetrations around taps, shower roses and any pipes through the waterproofed area.
- Floor falls to the waste, created in the screed before waterproofing, so water drains instead of pooling.
- Full curing of the membrane before tiling starts.
Which areas need waterproofing
AS 3740 treats different parts of a wet area differently. The shower area needs the most protection, while the rest of the bathroom floor and the walls around baths, basins and laundry tubs need waterproofing or water resistance to a lesser extent. The exact requirements depend on the room layout, so they are best confirmed during the quote.
Signs your shower waterproofing has failed
- Damp, bubbling or peeling paint on the wall behind or beside the shower.
- Swollen or stained skirting boards, architraves or vanity kickboards.
- Loose or drummy tiles, and grout that keeps cracking.
- Mould that returns quickly after cleaning, or a persistent musty smell.
- Water marks on the ceiling below an upstairs bathroom.
Can a leaking shower be fixed without re-tiling?
Sometimes. If the membrane is sound and the leak is through failed silicone or cracked grout at the joints, removing and replacing the silicone and grout can stop it. If the membrane itself has failed, the tiles have to come up so the shower can be waterproofed again. An inspection will tell you which it is.
Need this done properly?
ASA Tiling is based in Dandenong and works across Melbourne within 100 km. Call for a site visit and written quote.