Wet room shower former support

[jamesmerrix]

Hi,
I am installing a grp shower tray former on timber joists and I am struggling to get them perfectly level. is there anything wrong with laying 18mm boards on top of the joists and then the former on top of that.
I’ve dry fitted out and it feels much more secure, but I’m not sure if I’m missing something.
It will all be tanked before tilling.
if it is ok, can I use 18mm MR chip board? thanks for your help.
link to the tray I am using bellow.

https://www.contour-showers.co.uk/products/wet-floor-areas/showerdec-floor-former#ae-image-0

 

[bobasd]

Yes, fix any 18mm board to the joists to bring the floor flush.
Make sure the 18mm board is supported at edges and screwed down.

Dry fit with the trap and waste connected - will they later be accessible?

 

[jamesmerrix]

Thanks - I will fix the tray to the boards.

As for the waste - it won’t be accessible after its all tanked; but thats nothing to do with the boards underneath.
I am using this: https://mcalpineplumbing.com/wet-ro...e-50mm-water-seal-gully-tiled-or-stone-floors