dj - this is some advice I gave another poster a while ago about a tiled bath panel:
Make the framework from treated batten (25 x 50), it just needs to be screwed together. 2 rectanglular frames, big one length & height of bath with a couple of verticals equally spaced; the smaller one the size of the end of the bath minus the thickness of the big frame. These two frames can be screwed together to form a corner, then the whole thing is pushed into position under the bath. It only needs to be screwed to the floor - this framework will be very rigid. You will have to factor in the thickness of the ply base for the tiles (say 10mm) & the thickness of the tiles.
Ok, how to tile the panel? Assume you're using exterior grade ply (moisture resistant). DO NOT use wall-tile adhesive to fix the tiles to ply - the tiles may not stick permanently.
Method:
Dry fit panel to framework to make sure of clearances, ease of fitting, etc.
Remove the panel from the framework and lay flat, we usually do this over the bath if space is tight or otherwise on the floor. This is where you tile. Fix the tiles to the ply using solvent GRIPFIL - apply the Grip in a square , say 10 to 15mm in from the edge, around the back of the tile and a dot of Grip in the centre. Set the tiles on the ply by sliding into position, position with spacers, allow to set. Remove spacers, lift panel into position, masonary drill through the tiles to provide holes for your chrome capped screws into the batterns, screw into position, put the caps on (otherwise the threaded holes will get blocked-up with grout. Then grout with waterproof stuff. When all is dry run a bead of decent silicon along underside of bath rim/top of panel intersection.
So you don't tile with the panel in situ.
