The all important bathroom waterproofing

Where I live bathroom waterproofing or indeed waterproofing any wet area is not a matter of choice, but it is the law. All new work has to be inspected and certified correct under the provisions of the BCA (Building Code of Australia).

setting bath in wall
Bathroom waterproofing- A detail of the bath / wall layout.

I believe that the most important thing I did in the whole renovatin was the bathroom waterproofing job, to do it well and to get it inspected and approved before I covered it up with ceramic tiles.

Partly of course I did it because I was going to sell the house when my small renovation project was complete, and so I needed that waterproofing certificate along with all the other paperwork to reassure prospective purchasers.

The main reason though is that I have seen some terrible disasters when the old style waterproofing measures break down. Water running under walls and rotting out carpets in adjacent rooms. Water persistently ruining ceilings below.

Bathroom Waterproofing, Wet Area Walls and floor.

The BCA requires that all new wet areas, that is kitchen splash back, laundry, WC and bathrooms be waterproofed with an approved flexible membrane system, prior to the fixing of ceramic tiles. On new houses inspections are required before proceeding with the ceramic tiling.

Otherwise excellent bathroom work has in the past failed the test of time, due to building movement. Different rates of movement between the bathroom floors and walls. Sometimes the internal walls are a different construction to the external bathroom walls.

There are many different kits for doing the job. I got my waterproofing and tiles from a shop that imports quality tiles from Italy and Europe, and I went with the Mapei (Italian manufacturer) system, for both the bathroom waterproofing and the tile adhesive. I prefer to get materials like this from a specialist shop, rather than a general hardware store. A few words of informed advice from someone who has "been there and done that", can make all the difference.

Here is a quote from Mapei tech sheet -

"Mapegum WPS is a ready-to-use, solvent-free, single component, grey-coloured paste with a base of synthetic resins in water dispersion. Mapegum WPS has a thixotropic consistency which makes it easy to apply on horizontal, sloping and vertical surfaces. After rapid evaporation of the water content, Mapegum WPS forms a flexible membrane which is not sticky and which is strong enough to withstand light pedestrian traffic. It also forms an excellent surface which bonds perfectly to adhesives used for laying ceramics"

The real break though with these type of products is indicated by the word "flexibility".

etail at the floor-wall joint
Bathroom waterproofing- Detail of the floor-wall joint.

On our first house (timber frame) I fixed the ceramic tiles in the bathroom and WC onto two layers of 6mm flat cement wall sheets.

After about 3 years a crack appeared in each tiled wall, straight on the joint line of the cement sheets, which happened to be right in the middle of a tile.

What a bummer! The tiles were set solid, but the expansion, contraction and other movements in the timber frame inevitably caused something to give. The movement was probably very small, but white shiny ceramic tiles being what they are, the cracks stuck out like dogs balls.

The point I am making is that if I could have used one of the modern flexible bathroom waterproofing compounds that are available today, the cracking of those tiles would not have happened. The bathroom would still be acceptable.

bath edge detail
Bathroom waterproofing - Detail at the front of the bath.

So, even if you don't have to comply with any bathroom waterproofing regulations, I highly recommend you waterproof your bathroom before fixing the ceramic tiles. Don't build it good enough for the next five years, until you sell the house! Build it to last.

Waterproofing is cheap and easy to do. If you can use a paint roller and a brush you can do it. It is definitely messy, but the good thing is that it is water clean up.

The BCA is quite complex in the minimum areas to be waterproofed, with variations where there are showers screens or not, whether the floor is concrete or some other construction etc. etc. In my case the minimum area to waterproof would have been 1500 radius from the floor waste with turn ups of 150 at the included walls and all around the bath. All around the bath/shower area to a min. height of 1800. If no shower screen is fitted the min. width should be 1500 from shower head. I did the whole floor and and almost all the walls to a height of 2000. (I purposely left the bit behind the cupboard, in case I ran out of material, and sure enough I had a small patch that didn't get covered).

I don't see any point in trying to save the odd square metre here or there as the regs are quite complex so it is always better to do extra rather than get a knock back and have to do extra, along with the delay and extra inspection fee.

My tile height was 2100 (top of door frame). If I had been cheap and only done the exact area that the code requires I might have saved $30. Here's how I did it:-

  • Removed all loose surface material to the area being done. Broom and wipe down with wet sponge.
  • Primed the whole area with Mapei primer. (roller and brush). Which is a watery milky looking liquid that runs like hell. Soaks in and dries clear.
  • Applied the first coat of the compound, which is half way between thick paint and butter in consistency. As they say in the blurb, it is thixotropic. I again used a long nap roller and paintbrush.
  • Top gun tilers use trowels, faster and easier to clean. The coat shouldn't be too thick though.
  • 1mm thick is the recommended thickness.
  • The following morning I set in the reinforcing strips of fiberglass tape over all the corner joints, walls to walls and walls to floor.
  • The tape looks for all the world like a paper kitchen towel roll, but it is a very strong fiberglass material. The roll is 150 (6") wide.
  • I worked on one corner at a time, painting the area with compound, laying in the tape, dabbing it into position with the brush. This job is fairly messy, I use rubber gloves. The material does'nt go off very quickly, so you have a good amount of time to pull any twisted or wrinkled pieces off and to start again.
  • When I was happy that all the corners were taped up OK I did a final roller and brush coat over all the lot again.
  • That was it finished, two full coats everywhere and extra at the corners bedding in the fiberglass tape,
waterproofing to bathroom walls and bath
Bathroom waterproofing

It's a poor photo again, a wider angle would have been nice. Here is it ready for the inspection. Note the fan in the window, it is a cheap floor fan that I tied temporarily in place to suck out dust.

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Please Note! The information on this site is offered as a guide only!  When we are talking about areas where building regulations or safety regulations could exist,the information here could be wrong for your area.  It could be out of date!  Regulations breed faster than rabbits!
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