Five waterproofing mistakes that wreck Brisbane bathrooms

Waterproofing is the part of a bathroom you never see again once the tiles go down, which is exactly why it's the part that gets rushed. Here are the five mistakes I photograph on strip-outs, roughly in order of how much they'll cost you later.

1. Membrane over a wet or dirty substrate

Membrane doesn't stick to dust, and it doesn't cure over moisture. I see bathrooms where it was rolled straight over yesterday's screed or a floor someone swept with a broom. It peels like a sticker. Proper prep is a vacuum, a primer, and a dry slab, boring, unphotogenic, non-negotiable.

2. One thin coat where the standard wants two

AS 3740 calls for a membrane system, which in practice means two coats at the right thickness, not one generous pass. The difference is invisible until water finds the pinholes, usually into the unit below around year three.

3. Skipping the flood test

A 24-hour flood test before tiling is the only way to know the membrane actually works. It costs a day. Skipping it means the first real test is your shower, every day, forever. We do it on every job and send the photos to you and the building, our bathroom process has it as step five, not an optional extra.

4. Treating the shower screen as waterproofing

Glass and silicone are the last line, not the system. I've opened bathrooms where the 'waterproofing' was the screen installer running a fat bead and hoping. Water goes behind tiles, sits in the screed, and rots everything it can reach.

5. Puncturing the membrane for the vanity or rails

Every screw through a membrane is a leak path: grab rails, vanity fixings, shower screen channels. It needs planning: fixings marked before tiling, membrane-friendly anchors, or surface-mount where it works. Drilling blind through tiles and hoping the silicone catches it is how ceilings below get stained.

Waterproofing is 40% of a bathroom budget because it's 100% of what keeps the bathroom from being a demolition in five years.

How to not get caught

Ask your builder for membrane photos and the flood test record before tiles go down. Any builder who does it properly will hand them over happily, I keep a folder per job. And if you're buying a unit with a recently renovated bathroom and there's no waterproofing certificate in the paperwork, negotiate like the risk is real. Because it is.

Think yours might be failing? Bubbling paint on the other side of a bathroom wall is the classic tell. Send us a photo and we'll tell you what we're looking at.