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How to waterproof bathroom?

Hi everyone,

I have just had the screed layer removed from the bathroom floor and will be getting a concreter to come and pour the new bathroom floor which will then be sealed and used as a concrete floor and shower base without any tile. Can you please advise what sort of waterproofing needs to happen around the base of the wall prior to the concrete pour, and/or afterwards. Does some sort of waterproof membrane need to be laid and extend up the walls before the concrete goes in? The grey section along the edges is a very hard plastic that was the edge under the screed. Thanks.

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JacobZ

Hi @JSLawrence,

Thank you for your question about waterproofing a bathroom and apologies for the delayed response.

As waterproofing is a licensed industry, I'd suggest you contact a waterproofing contractor for their guidance on the process.

With this being said, the National Construction Code (NCC) states the following in Part 10.2 Wet area waterproofing - Section 10.2.3 - Area outside shower area -

For concrete, compressed fibre-cement and fibre-cement sheet flooring, the floor of the room must be water-resistant.
For timber floors including particleboard, plywood and other timber-based flooring materials, the floor of the room must be waterproof.
Wall/floor junctions must be—

a. waterproof; and

b. where a flashing is used, the horizontal leg must be not less than 40 mm.

As you are looking to have concrete as the finished floor surface, a waterproof membrane can and should be installed underneath the concrete. The main reason for this is that to achieve a waterproof wall/floor junction, the membrane needs to extend 40mm onto the "horizontal leg", which in this case is the concrete floor. If you are looking to use concrete as a finished floor surface, having a strip of waterproofing around the edge of the room won't look particularly nice.

I'd suggest discussing the best way to go about this with a licensed waterproofer.

Let me know if you have any further questions.

Jacob

JSLawrence

Hi team,

I recently removed the 50mm screed layer from our bathroom and am seeking to fill the 50mm deep void with concrete reinforced with steel mesh. Can you advise if this is thick enough to avoid major cracks in the concrete? One of the concreters I’ve been speaking with is wary of doing the job as he thinks it will crack. If it’s on top of concrete though and the existing concrete is wet before pouring, won’t the new concrete bond to it and strengthen the whole thing? He has questioned whether I just use the existing concrete base and have a step down into the bathroom. I’d love to hear your thoughts please? My other problem is the concrete sheets on the wall have a 50mm gap at the bottom as they were installed before the screed was removed, so was planning to build the floor level back up to meet the concrete sheets. Thanks for your help. This is turning into a very painful job to try to manage with very few tradies who will come out to our rural property. So doing our best. Thanks for your advice and thoughts.

Jewelleryrescue

Hi @JSLawrence

Yes 50mm is plenty strong enough for a regular garden path. 75mm is the minimum drive way thickness for cars (not regular trucks parking though)

Your 50mm is super golden

I would go as thin as 30 mm for regular concrete. Rare hair cracks can be filled under tile on top of the original slab they arnt an issue or weakness needing ripping up.

Worst case senario a crack forms. Simply fill it with regular cement no sand.

Make sure you follow the bag mix ratios for general purpose cementing (do not put in extra cement as this will cause cracking for sure.)

Yes the steel will help mid way into slab thickness.

This step not really necessary as the new slab wont really move in situ as it is framed by walls. But In case of future jobs.

To intergrate the bottom slab into the top slab use a lump hammer / Impact chisel. hit the old slab and put dents/chips in to lock the two slabs together every 300mm or so.

Hope you get your project finish with out to many hassles.

JacobZ

Hi @JSLawrence,

I've combined this post with your previous one as they give context that is relevant to each other.

Concrete poured in separate batches does not bond to each other well. You can use a bonding agent such as BondCrete Cement Additive to help them cling to each other better, but ultimately there will always be a weakness between the two concrete surfaces and knowing that you will be applying a waterproof membrane beneath the concrete, this is not really an option.

If you add a waterproof membrane beneath the concrete, you would be protected if it does crack, but as your concrete is going to be used as a finished floor, this might not be ideal.

Unfortunately, it's likely best to follow the advice of the professionals. The suggestion to use the existing concrete floor is likely your best option.

You can always replace the wall sheets, so they run closer to the existing concrete. This might even work out cheaper than having a concreter come and install new concrete.

Let me know what you think.

Jacob

JSLawrence

Hi @Jewelleryrescue @JacobZ ,

thanks for your advice on this post. In the end concrete was proving too challenging so we have ended up going with screed and tiling again. We have a tiler coming tomorrow to start the screed, so will hopefully have a bathroom again by the end of Jan after 5 months without a bathroom lol. Thanks so much for your support!

EricL

Hello @JSLawrence

It's good to hear that you've settled on a course of action. I'm sure you are looking forward to getting your bathroom back after waiting for so long.

Please keep us updated with your progress, we look forward to seeing your bathroom re-assembled and ready for use.

If you need further assistance, please let us know.

Eric

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