Waterproofing across an expansion joint/ control joint

[ApeWrangler]

We are looking to create a shower/bath in the attached entryway photo. The door will be removed and the opening bricked up with a low wall about 400mm high +- and a window fitted on top of the wall. The idea is to build another nib wall to join the 2 walls at the bottom half of the picture at the same height (+- 400mm) and this will create the rectangular bath/shower area. Our issue is that wall on the left is part of the house structure and isolated from the slab, which is part of the garage, by an expansion/control joint. There is a dark foam strip there so it is hard to see in the photo and the gap is about 10mm. House is mid 70's construction and there is no indication of much movement between the two bodies in the past. I understand that the 2 low joining walls will need to be 'free standing' from the left wall and will need re-inforcing rods epoxied into the concrete and be tied to the RH wall.
Our issues are...

1. how to waterproof across the current expansion joint?
2. how to waterproof across the control joints at the LHS of each low wall that will be the ends of the bath/shower?

Left and right wall will be insulated to reduce heat transfer and the bath floor will be slightly raised and insulated for same.

[havabeer69]

won't you but cutting up a chunk of the slab for a drain?


simple option would be to put a shower tray at the bottom and waterproof your wall sheets into it. there's trays with inserts if you want to tile the bottom. at least that way you don't have to water proof the control joints.

[mic-d]

This makes a lot of sense but then the sheet that’s attached to the left hand wall may move relative to the rest of the structure. You’re still going to need flexible control joints between the tiles and the tray and the vertical wall/window joint. This is such a foundational step in the bathroom that you want to get it right. The cost of getting professional assistance would be far less than rectifying it later

[ApeWrangler]

Thanks guys. Much appreciated.
Yes, floor waste will be cut into the slab. Not sure how this would affect the water proofing of the control joint?
My concern with the shower tray idea is like mic-d says, you still have to seal a moving joint where the wall tiles meet the tray.

Am chasing up professional input today.

[droog]

My concern with the shower tray idea is like mic-d says, you still have to seal a moving joint where the wall tiles meet the tray.

Sure there is a movement joint but the sheet and tiles overhang the lip on the tray presenting less of a risk than with a waterproof membrane.

Waterproofing for any joint where movement is to be expected should be addressed with a bond breaker and a bandage bridging between the separate surfaces. There are bandages that include a bond breaker in them.
https://www.bostik.com/australia/en_...mpfix-bandage/
You will need to look and find a compatible system for all the products, ie bond breaker, bandage, waterproofing and tile adhesive.