Fixing a shower chair to a plasterboard wall

[Lieutenant Columbo]

My mother is disabled and has a wetroom but no shower chair to sit on.
The plasterboard walls are all tiled.

Frankly I don’t trust any of the fixing options available.
My plan is to remove the tiles on the desired wall and but away the plasterboard and replace with plywood, then retile.

Is 18mm plywood strong enough to hold the fixing screws?
What else could I do to strengthen the walls?

What is the gold standard in this situation.
I want peice of mind knowing that my mother is safe and that the chair won’t come away from the wall at some point in the future.

 

[Keithmac]

Can you not build a frame up after taking the plaster board off?, the chair will be fixed to the frame which is secured to floor and ceiling joists.

Mark where the frame is, ply and tile then drill through so the chair is directly fastened to the frame inside the wall.

 

[^woody^]

Use Hardiebacker and a timber noggin.

 

[noseall]

This sort of critical fixing always involves removing the plasterboard on the other side, if you haven't already.

 

[Lieutenant Columbo]

Use Hardiebacker and a timber noggin.

What’s that?

 

[^woody^]

Hardiebacker is a tough water resistant cement board for wet areas.

A timber noggin is a timber noggin.