Extending an external corner minimally to accommodate a wider shower tray?

[RobRazor]

Hi. Hopefully I’m in the right area for this query. I’m trying to extend a a recessed area of my bathroom to accommodate a wider shower tray. Depth of area is 740mm. The depth is measured along a block built airing cudboard which protrudes into the corner of this room. I originally planned to use a 700 x 1400 tray to install but it’s obvious the tray feels very restricted for the 700mm depth. So I would like to upgrade the tray to the next depth size which is 760mm. This would mean extending the width of the airing cudboard back wall by around another 20 or so mm. This could be for the full protrusion part of the wall of the airing cudboard or just a knib on the external corner. As it is an external corner which would be tiled, and thinking the extended wall width may be created from wood battening and tile backer board. I’m concerned that a tray glass screen on this edge might create movement on the built up external edge of tiles. The depth creation would be fairly quick using battening and backer board compared to creating a brick/ block stitch knib extension to the wall. Sorry bit long winded. Wondered if anyone had some better ideas from their experience?

 

[martygturner]

Hardwood ply comes in 20mm so sheath the knib in that , you can paint on some waterproof membrane and then fix to the ply.

 

[RobRazor]

Hardwood ply comes in 20mm so sheath the knib in that , you can paint on some waterproof membrane and then fix to the ply.

Thanks for that suggestion Marty. Yes did cross my mind as thick ply like marine ply has a sturdy edge. My main worry is I will be tiling onto the knib or return wall. Won’t the ply seasonal movement affect the tiles? Also thought of sheathing both sides of the external corner with the thickest cement board then screwing into edge sheet overlaps.

 

[martygturner]

Ply will be fine, think of the number of bathroom floors that are made of the stuff then tiled. Just use a good adhesive. such as Bal C2FES1, it allows flex of 2.5mm and allows for tiling direct to plywood. Cement Board will not have the pull up for fixing the shower screen to it.