Shower and wet area waterproofing
Waterproofing for showers, bathrooms and laundries in Toowoomba 4350: leak signs, what the NCC and AS 3740 require, QBCC licences and price ranges.
Waterproofing is the membrane under the tiles that keeps water in the shower and off the floor frame. Once it fails, regrouting rarely stops the leak, and the usual fix is to strip the shower back, apply a new membrane and retile. Published Brisbane ranges for wet area waterproofing are $35 to $80 per sqm, and each quote you receive comes from an independent provider who carries out the work.
Signs a shower is leaking
- Paint bubbling or skirting swelling on the other side of the shower wall.
- Damp carpet or timber floor near the bathroom door.
- Stains or mould on the ceiling under an upstairs bathroom.
- Tiles on the shower floor that move, crack or sound hollow.
- A musty smell that comes back after cleaning.
- Grout that stays dark long after the shower was last used.
Not every damp patch is the membrane. A leaking tap body, shower mixer or waste pipe can look the same, which is why a plumber sometimes checks first.
Repair options compared
| Option | When it works | Limits |
|---|---|---|
| Regrout and reseal | Water is getting in through cracked grout only, membrane still sound | Short term if the membrane has failed |
| Penetrating sealer over tiles | Minor surface absorption | Not a substitute for a membrane |
| Remove shower floor tiles and remake the base | Leak is at the floor or waste, walls sound | Wall to floor join must be redone carefully |
| Full strip of the shower | Membrane failed on walls and floor | Most cost, new tiles may not match the rest |
What the rules require
The NCC 2022 Housing Provisions, Part 10.2, set the minimum for domestic wet areas. Among the points on the ABCB wet area waterproofing page:
- The shower floor must be waterproof, including any hob or step down.
- Shower walls must be waterproof to at least 1800 mm above the floor substrate.
- Wall and floor junctions and penetrations such as taps must be waterproof.
- Outside the shower, concrete and fibre cement floors must be water resistant, while timber based floors must be waterproof.
- Where a floor waste is fitted, the fall to it must be between 1:80 and 1:50.
AS 3740 is the Australian Standard for waterproofing domestic wet areas, and the NCC refers to it. Membranes also have their own manufacturer instructions for coats, thickness and cure times.
Which licence covers waterproofing?
Two QBCC licence classes are relevant. The wall and floor tiling class includes applying waterproofing for wall and floor tiling. The waterproofing licence class covers applying, installing and repairing waterproofing, including surface preparation. Either way, check that the person signing your contract holds a licence that matches the work. Moving drains or the shower waste is plumbing and drainage work, which the QBCC says needs a licence at any value.
How a shower is rewaterproofed
- Tiles, screed and any damaged sheeting removed, with an asbestos test first in a house built before 1990.
- Framing and floor checked and dried, rotten timber replaced.
- Floor waste and puddle flange set at the right height by the plumber where needed.
- Floor screeded to fall towards the waste.
- Primer, then bond breakers or flexible sealant at corners so the membrane can move.
- Membrane applied in the coats the product requires, lapped up walls and over the hob or waterstop.
- Full cure, inspection, and in some cases a flood test, before tiling.
How long does it take?
A shower strip, rewaterproof and retile usually runs over several days, because each layer needs time. The screed needs to set before the membrane goes on, the membrane needs its full cure before tiles, and the adhesive needs to set before grouting. Cold Toowoomba winters stretch those gaps. Plan to be without the shower for the whole job, and ask for the expected timeline in writing.
What does waterproofing cost?
From the published Brisbane ranges in this cost guide:
- Waterproofing: $35 to $80 per sqm
- Removing old tiles: $20 to $55 per sqm
- Wall tiling labour after the membrane: $40 to $100 per sqm
- Floor tiling labour: $40 to $90 per sqm
A leaking shower almost always involves retiling as well, so the real cost is closer to a bathroom tiling job than to the membrane alone. The cost guide explains what else goes into a quote.
What a careful waterproofer will not do
- Promise that a sealer brushed over the tiles will fix a failed membrane.
- Tile over a membrane before it has cured.
- Skip the corners and junctions where most leaks start.
- Waterproof over wet or rotten timber.
- Guess at the cause of a leak without ruling out the plumbing.
Toowoomba showers
Many older Toowoomba houses are timber framed with timber floors, and in a high set house the room under the bathroom may have been built in later. A slow leak there can run for years before anyone sees a stain. The NCC rule that timber floors outside the shower must be waterproof matters in these houses. Cold weather also stretches cure times, so a tiler working in winter on the range may need an extra day between membrane and tiles. Read more about local housing on the Rangeville and Toowoomba pages.
Next step
Take photos of the shower floor, the wall on the other side and any stains, and send the leak details through the quote form.
Frequently asked questions
- How do I know if my shower is leaking?
Look for paint bubbling, swollen skirting or damp carpet on the other side of the shower wall, stains on the ceiling below, and loose or hollow sounding tiles on the shower floor. A musty smell that returns after cleaning is another sign. A plumber can rule out leaking pipes first.
- Can a leaking shower be fixed without removing the tiles?
Only if the water is getting in through failed grout or sealant and the membrane underneath is still intact. Regrouting and resealing can then help. If the membrane itself has failed, products brushed over the tiles will not fix it, and the tiles need to come off.
- What is a flood test?
Some providers block the shower waste and fill the base with water once the membrane has cured, then check for leaks before any tiles go down. Not every job includes it. Ask how the provider checks the membrane, because once tiles are laid it is too late to see a problem.
- Does my home warranty cover a leaking shower?
It depends on when and how the work was done. Where tiling or waterproofing over 3,300 dollars was done by a licensed contractor, the Queensland Home Warranty Scheme may apply to defects within its time limits. The QBCC can explain whether your situation qualifies and what to lodge.
- Is waterproofing needed outside the shower?
Yes, to a lesser degree. Bathroom floors outside the shower need to be water resistant if they are concrete or fibre cement, and waterproof if they are timber based, with sealed junctions where floor meets wall. The NCC wet area rules also cover laundries, toilets and walls beside baths and basins.