Wetroom floor levelling problem

[Peter Lee]

The wetroom I am about to start building has a floor area 900 x 1850. The former is a GRP 900 x 1400 x 22 so I need to fill the 450 x 900 space at the end of the former. I considered putting a 9mm ply base down with 12.5mm backer board over the top which will bring the level up to within 0.5mm. The area that I have to raise is in front of the basin so will take a fair amount of standing on and I am concerned that the backer will eventually compress a bit or the whole thing flex. I intend to put mapiband tape across the former/backer junction then Schulter Kerdi membrane over the entire floor area. Any suggestions about a better way of filling the 450 x 900mm space gratefully received.

 

[Albert]

The wetroom I am about to start building has a floor area 900 x 1850. The former is a GRP 900 x 1400 x 22 so I need to fill the 450 x 900 space at the end of the former. I considered putting a 9mm ply base down with 12.5mm backer board over the top which will bring the level up to within 0.5mm. The area that I have to raise is in front of the basin so will take a fair amount of standing on and I am concerned that the backer will eventually compress a bit or the whole thing flex. I intend to put mapiband tape across the former/backer junction then Schulter Kerdi membrane over the entire floor area. Any suggestions about a better way of filling the 450 x 900mm space gratefully received.

You could go with 2, 10mm backer boards with 2mm of tile adhesive between

 

[Qwerty]

You would be far better off bracing between the joists with noggins to firm it all up, and lay hardifloor 22mm. Either that or 18mm WBP ply then 4mm waterproof backerboard.

I am assuming it is on a suspended floor of course!

 

[Qwerty]

You could go with 2, 10mm backer boards with 2mm of tile adhesive between

This would be my suggestion on a solid floor

 

[Albert]

This would be my suggestion on a solid floor

My mistake i just assumed it was.

 

[Qwerty]

It could well be. @Peter Lee is it wooden suspended or solid?

 

[Peter Lee]

Yes it is suspended. I had an alternative thought. I have some fairly extensive levelling to do so whilst I am about it I could simply raise the last 450mm up by 4mm relative to the rest. I could then put in a section of 18mm ply, seal it then fleece over the lot.