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How to waterproof a bathroom

How to waterproof a bathroom!

There are a few tricks when it comes to waterproofing a bathroom yourself during the big renovation. If you're a confident DIY-er you can probably have a good go yourself but if you're not that confident you may want to get your builder or a specialist waterproofer to come in and get the job done- especially if it's a complex or large bathroom area.

The thing is with waterproofing your bathroom- you need to get it right the first time. No ifs buts or maybes- it needs to be done properly. Doing a half-arsed job will end in tears when your kids create a bath-time tsunami and water slops over the edge of the bath, making a grand entrance through your downlights below.

Even if the leak is slow, it can actually end up being worse, because over time the damage is being done out of sight and you'll end up with damp, sodden and collapsing ceilings underneath.


I can't stress enough how really important it is to get rid of every spec of dust from the process of ripping off old tiles and old flooring. Dust, grease and debris is bad news for waterproofing so make sure you've swept, mopped and wiped down all of the floor and wall area.

Waterproofing a bathroom - make sure you clean all of the dirt away first

There's a list of things you need to do before you start waterproofing- making sure the flooring is level and up to scratch and that you're ticking boxes when it comes to working within code for your shower, plumbing and so on- but you've already done all that right?


You'll still have small gaps between the floor and wall no doubt, but that's fine just for the minute. Using a primer (typical would be primer and additive mix from a hardware store), roller the primer across ALL of the floor and up to about 20-30cm on the wall, plus all of the areas where you'll have the shower and bath splashing.

Once that's dry, you need to get a good silicone sealer and run it over all of the gaps in the floor, all of the corner joints and anywhere where there are joints between wall and floor. If your house moves a little over the years, the silicone will bend and flex enough to maintain a seal.

Apply primer around the adges and up to 20-30cm on the wall


Just like when you paint, you want to contain the waterproofing agent, so use your masking tape to confine where you're going to waterproof, remembering we primed to about 20-30cm from the floor up the wall. If you're waterproofing a shower area then the standard height is 1.8m. It's a good idea too to cover with tape any pipes to avoid getting the agent everywhere. (allow a few cm of pipe to be water-proofed too!)

When it comes to waterproofing agents, there are a few variations you can use such as under tile or wet area waterproofing. We'll use the general one to start the process. Roller the agent on the wall within your masking tape boundaries and once you get to the floor, just do a roller-width onto the floor- I guess it's like cutting in when you paint. Below you'll see we did our first level of primer and water proofing in the shower recess BEFORE the screed went down. You'll apply waterproofing again on top of the screen, then the tiles on top of that.


You'll need a membrane roll which is used to cover the gaps between the floor and walls. Something like a Crommelin reinforcing fabric which is a roll of material used to to provide support for the areas with gaps. Cut the rolls into strips the length of your walls and push up against the wall and floor so that half covers the floor and half covers the wall. Then cover any other gaps in the floor and walls with the membrane strips- just paint the waterproofing onto it with a roller to stick it down.

Mebrane goes down around all of the gaps

Now you're ready to go nuts with the waterproofing agent, simply roller or paint the rest of the floor and areas, giving it a good thick coat. After about 12 hours, it should be ready for a second coat, so roller the next coat on and let that dry for about another 48 hours depending on the heat and humidity.

start with the agent around the wall and floor area then roller the whole of the floor and up to 1.8m high in shower area

And that's pretty much it! As with everything, do your research into the right type of products to use and what tools you'll need- but most staff at a local hardware store will be happy to show you what you need.

Thanks to my mate Zac Tranter, a professional waterproofer for some extra professional know-how.

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