Yes, you have to waterproof before tiling a bathroom, and in Australia it is not optional. Waterproofing a wet area to Australian Standard AS 3740 is a mandatory step under the National Construction Code, and in South Australia it must be done by a licensed applicator before a single tile goes on.
This guide explains what AS 3740 actually requires, which parts of a bathroom have to be waterproofed, why it is a licensed-only job, and what it costs in Adelaide. It sits within our complete guide to bathroom tiling in Adelaide.
Why tiles are not waterproof
The most common misunderstanding is that tiles and grout keep water out. They do not. Grout is porous, tile joints move and hairline crack over time, and water finds its way through. Behind a properly built wet area sits a continuous waterproof membrane, and that membrane is the thing actually protecting your home.
Without it, water tracks straight through the grout, soaks into the substrate, and reaches the timber framing and any room below. That is how you end up with rot, black mould, lifting tiles and a repair bill that dwarfs the original job.
What AS 3740 requires
AS 3740 is the Australian Standard for waterproofing domestic wet areas, and it is called up by the National Construction Code, so it carries the force of law. It sets out the minimum areas that must be waterproofed and to what height. The exact extent depends on the layout, but the core requirements are consistent.
At a minimum, a compliant bathroom needs:
- The shower floor waterproofed in full, and turned up the walls
- Shower walls to a set height above the floor (higher again inside an enclosed shower)
- The room floor waterproofed where there is no hob, or where the shower is unenclosed
- Wall and floor junctions sealed, because corners are where most leaks start
- Penetrations around taps, the outlet, the drain and any pipework detailed and sealed
- Hobs, steps and the base of the wall treated to stop water wicking upward
A wet room or hobless shower raises the bar further, because water is no longer contained behind a screen, so more of the floor and walls have to be treated and the falls to the drain have to be spot on.
Where waterproofing fits in the sequence
Waterproofing is not a step you can bolt on later. It has to go down after the substrate is prepared and before any tiling begins, and the membrane needs proper curing time before tiles are laid over it. Rushing that curing is one of the quiet causes of early failure.
If you are mapping out the job, the order you tile a bathroom in shows exactly where the membrane sits: prepare, waterproof, cure, then tile. Skipping the cure or tiling into a damp membrane undermines the whole system.
Why it has to be a licensed job
In South Australia, waterproofing a wet area is restricted building work. It must be carried out by a licensed waterproofer, or a builder licensed to do that work, not a general handyman and not the homeowner. There are good reasons this is regulated:
- A membrane that fails is hidden behind finished tiling, so mistakes are invisible until the damage is done
- Getting the membrane heights, junction detailing and falls right takes training and the correct products
- Building insurance and warranties generally will not cover water damage traced back to non-compliant, unlicensed waterproofing
- If the work is ever inspected or you come to sell, non-compliant waterproofing is a problem you inherit
This is why waterproofing is almost always itemised separately on a tiling quote. A licensed operator wants you to see it has been costed and done properly. Be wary of any quote that folds it into a vague lump sum or leaves it out altogether, which is a classic sign of a corner about to be cut.
What bathroom waterproofing costs in Adelaide
Waterproofing is a modest line item next to the tiling itself, but it is the one you can least afford to skimp on.
| Job | Indicative Adelaide cost | | --- | --- | | Waterproofing a standard wet area | $500 to $1,500 | | Shower recess only | $400 to $800 | | Larger bathroom or wet room (more walls, more junctions) | $1,000 to $1,500+ | | Redoing failed or DIY waterproofing (includes tile removal) | Cost of the above, plus $20 to $40/m2 to strip existing tiles |
The bottom row is the important one. A DIY or unlicensed membrane that has to be torn out and redone costs far more than getting it right the first time, because the finished tiling comes off with it. You can size up the membrane portion with our waterproofing cost estimator, and see how it fits the whole job in our guide to bathroom tiling costs in Adelaide.
The bottom line
Waterproofing before tiling is not a nice-to-have or a step you can trim to save a few hundred dollars. It is a legal requirement under AS 3740, it must be done by a licensed applicator in South Australia, and it is the single thing standing between your tiles and a rotted-out bathroom. Done right, you never think about it again. Done wrong, it is the most expensive mistake in the room.
Make sure your bathroom is waterproofed properly
The safest move is to have a licensed tiler and waterproofing specialist handle the membrane and the tiling as one compliant job. Tell us about your bathroom and we will connect you with vetted, licensed Adelaide bathroom tilers who waterproof to AS 3740 and itemise it clearly, so you can compare free quotes with no obligation.