How to waterproof bathroom?

[JSLawrence]

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.

[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 -

1. For concrete, compressed fibre-cement and fibre-cement sheet flooring, the floor of the room must be water-resistant.
    
2. For timber floors including particleboard, plywood and other timber-based flooring materials, the floor of the room must be waterproof.
    
3. 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