There is no separate price for bathroom waterproofing on our price list, and there will not be one, because waterproofing is priced within the renovation scope rather than as a stand-alone line. Anyone who gives you a per-square-metre or per-bathroom waterproofing figure over the phone is guessing at a number that depends on the layout, the substrate and the membrane system, and I would rather explain how it is actually priced. The more useful thing this page can do is tell you what waterproofing must cover in Queensland, why it can never be rushed, and what it costs you when it fails.
Where waterproofing sits in the renovation budget
| Renovation component | How it is priced | Notes |
|---|---|---|
| Plumbing scope, mid-tier renovation | $6,000 to $9,000 plumbing portion | Strip-out, rough-in, fit-off, pressure testing and the Form 4 |
| Waterproofing, licensed to AS 3740 | Priced within the reno scope | Done by a licensed waterproofer; you must receive a certificate |
| Contingency for hidden damage at strip-out | Allow $2,000 to $3,000 | Rotten subfloor and old failed membranes are the usual finds |
| Full renovation total | Quoted on inspection | Tiles, fixtures and joinery swing it more than any single trade does |
Why is there no per-square-metre price?
Because the number would be meaningless without the scope behind it. Two bathrooms of the same floor area can need very different waterproofing: one has a hobbed shower in a corner and a tiled floor on a concrete slab, the other has an open walk-in shower with no hob, a timber subfloor and a freestanding bath against a wall. The second one needs the membrane over the entire floor and up more wall, with more junctions and penetrations to detail, and it takes longer to prepare and cure. Then there is what turns up at strip-out. Older bathrooms on the Gold Coast often hide a failed membrane, a soft floor or water-damaged framing under the tiles, and none of that is visible until the old tiles come off, which is exactly why we tell every renovation customer to hold $2,000 to $3,000 in contingency. Waterproofing is quoted as part of the whole renovation, on inspection, with the substrate known, and that is the only way the number means anything.
What does AS 3740 actually require?
AS 3740 is the Australian Standard for waterproofing domestic wet areas, and in Queensland waterproofing is licensed work carried out to it. In plain terms, the standard sets out which surfaces must be waterproofed and how the membrane has to be detailed at every place water could get through. The details are the waterproofer's job, but as the homeowner it helps to know roughly what should be covered.
- The shower recess. The whole floor of the shower and the walls to a set height above the floor, with the membrane carried into the floor waste and around every tap and outlet penetration.
- The whole bathroom floor in some layouts. Where the shower has no hob or screen to contain water, and where the floor is timber or sheet flooring rather than concrete, which covers most upper-storey bathrooms, the membrane runs across the entire floor and up the walls.
- The bath. The floor around the bath and the walls it sits against, so splash and overflow cannot get behind it.
- Basin and other wet areas. The wall behind a basin and the floor around it, with the junction between wall and floor sealed continuously.
- Every junction and penetration. Wall-to-floor corners, the floor waste, tap bodies and any pipe coming through the membrane are the points where water gets in, and the standard is mostly about getting those right.
The point of listing this is not so you can inspect the membrane yourself. It is so you can ask the waterproofer what is being covered and why, and so you recognise a scope that skips the floor outside the shower or stops the membrane short of the height it should reach.
Why waterproofing sits between rough-in and tiling
The sequence in a bathroom renovation is fixed for a reason. The plumbing rough-in goes in first: the floor waste, the tap bodies, the mixer, the waste and vent pipes, all set to the exact positions of your chosen fixtures and pressure tested. Then the waterproofer comes in and seals the room, detailing the membrane around every one of those penetrations. Then the tiler covers it all. Once tiles are down, the membrane is buried, which is why it has to be right first time and why the plumbing has to be finished and tested before the waterproofer starts. Move a tap after the membrane is on and you have cut a hole in the one layer that was keeping the water in.
It also cannot be rushed. Membranes need their full cure time between coats and before tiling, and a waterproofer who is pushed to hand the room over a day early is being asked to hand over a membrane that is not ready. Skipping it altogether, or having someone unlicensed do it to save a few days, is the single worst corner you can cut in a bathroom. In Queensland, bathroom renovation plumbing is licensed, notifiable work lodged on a Form 4, and waterproofing is licensed work with its own certificate. Both pieces of paper exist because both jobs are invisible once the room is finished.
The certificate you must receive
When the waterproofing is done, the licensed waterproofer issues a certificate stating that the work was carried out to AS 3740. You must receive this. Keep it with the Form 4 for the plumbing, because between them they are the proof that the two hidden parts of your bathroom were done properly by licensed people. Your insurer will ask for them after a water damage claim, a buyer's solicitor will ask for them at sale time, and if the membrane ever fails, the certificate is what the warranty and complaint processes run on. If the person who waterproofed your bathroom cannot give you a certificate, that tells you something about whether they were licensed to do it in the first place.
What does failed waterproofing cost you later?
More than the whole renovation, sometimes. A failed membrane does not announce itself. Water goes through the grout, past the membrane and into the floor or wall behind it, and the first sign is months later: paint bubbling on the other side of the wall, a stain on the ceiling below in a two-storey home, a skirting board that has gone soft, tiles that sound hollow when you tap them, or a smell of damp that will not go away. By then the framing, the subfloor and sometimes the room next door are wet. The fix is not a bead of silicone. It is stripping the tiles, cutting out and replacing the damaged floor and framing, re-doing the plumbing penetrations, waterproofing again properly, tiling again, and repairing the room next door as well. You are paying for a second bathroom renovation plus the damage, and if the original work was unlicensed or uncertified, your insurer may not be there to help. That is the whole argument for paying for waterproofing properly inside the renovation scope the first time.
How to get a real number for your bathroom
Get the whole renovation quoted on inspection, with the plumbing scope, the waterproofing and the contingency identified, rather than collecting a per-square-metre figure for each trade and adding them up. We price the plumbing portion fixed, typically $6,000 to $9,000 for a mid-tier bathroom keeping its layout, coordinate a licensed waterproofer inside the scope, and make sure the certificate and the Form 4 land in your hands at the end. Our bathroom renovation plumber page explains how the trades sequence around each other.
Planning a bathroom and want the waterproofing done properly the first time? Call Hills Plumbing & Gas on 0472 657 042 or start with our Bathroom Renovations service page. Fixed plumbing price, licensed waterproofing inside the scope, certificate in your hand. QBCC licence 15243081.