How to fill gap under inset bathtub to frame?

[samo]

Hello, new to the workshop so will do my best —

I'm currently reboarding and tiling the bathroom from existing post-purchase — I've taken out the tiles and plasterboards around the bath, when I was removing them, I noticed there were tile on tile to the short ends of the bath and a kind of rubber/silicone(?) mat along the long edge (under tiles) — after reboarding with 10mm Aquachek to the frame I'm noticing I have about a 6-7mm gap between the bath lips and the reboarded frame which is to be tiled, my tiles are 8mm thick so I can't tile underneath — my question is what is the best watertight solution to fill the gap to secure the weight of the bath (it now has some flex when weight is put on the unsupported sides. When I google/youtube inset bath installation most tubs it seems rest on the timber frame — I am hoping to avoid having to go down the route of re-framing. 

It is already mortared to the ground I havent moved the bath that was existing in place)  and to be able to waterproof and tile to the edge of the lip ...  the plan is to waterproof the board with crommelin and then re-tile and seal ... Any advice appreciated.6/7mm gapoverview of bath surround

[JacobZ]

Hi @samo,

A warm welcome to the Bunnings Workshop community, it is wonderful to have you with us.

My suggestion is to add 6mm Villaboard over the top of the Aquachek. Cut it to size and shape, slip it under the bathtub's lip, and fix it in place. This will maintain a perfectly flat surface that will support the tub properly, and you can waterproof and tile over it.

You can then seal the underside of the lip to the Villlaboard with silicone such as this SikaSeal Kitchen And Bathroom Silicone Sealant and waterproof as mentioned.

Let me know what you think.

Jacob

[samo]

Thanks Jacob, 

That sounds like some solid advice there and not too impactful — i'll look in to picking up some villaboard to keep the prject moving. 

Thanks for the reply!

Sam 

[JacobZ]

No worries @samo.

Keep us updated as the job progresses. I'd love to see how it all turns out.

Jacob