Bathroom wall not square. How to fix?

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Joe Shmoe

Established Member
8 Mar 2008
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Renovating a Bungalow bathroom for my mum, and will be fitting a new bath or shower. The bathroom is tiny, being only 1600mm square roughly.

Part of internal wall (1950s breeze block type) wasn't built square so a new bath or shower (not decided yet) won't fit nice. The old bath had a large gap at the end which was covered with tiles which looked awful and I don't want to repeat that, so I need to square the wall somehow. I can't lose too much space as a 1600mm bath only just fits in currently. (although has a 30mm gap on the left side of the end)

I have attached a diagram to help visually, but basically I need to pack out 30mm over 800mm so a bath or shower tray will fit in nice and square.

Should I use some battens (20mm on the left, and 10mm in the middle, and none on the right) and then attach aquaboard or something, or perhaps use render? Or couple of coats of bonding before skim? It's 30mm, so fairy deep so concerned about whether Bonding or Render will be OK at that depth.

Unsure if it will be tiled or showerpanels, but want to ensure that the corrected wall will be able to hold heavy tiles if needed.

If it helps, the whole bathroom has been stripped back to the original render as the skimcoat was falling away, and will be skimmed all over. Just want to know what to do with this angled wall before I get the plasterer in.

Any ideas would be great. Thanks folks.
Maybe if you install a walk-in shower then the only bit that heeds correction is the bit between the shower tray and the wall that is on the 'skunt'. I am assuming that the walls in the wet area can be tiled/paneled despite the non-right-angle corner. I am not experienced in bathroom design, so I may be about to suggest something wrong, but if you place the shower tray before tiling/panelling then some of the discrepancy could be hidden by the thickness of the tiles/panels. Not all 30mm for sure, but maybe half if you are lucky.
similar prob years ago....
wanted a one peice floor to ceiling mirror wall.....
got the plasterer in re redo the plaster taking out the inch half taper....
he used 3 coats of browning after going to bare brick.....this wall never got wet....

aqua panel is 12mm thick and very strong ue idea above will work.....
pre-treat the battens first or use galve strips
Joe, I've used the method you suggest several times for trueing up a corner. I've cut or planed tanalised roofing battens to profile/taper and then aqua panelled.
This method is perfect for trueing up a wall, allowing pipe space or eliminating condensation on a solid, cold outside wall.
The greatest sin [to me] is using plasterboard on walls that a bath or shower is in contact with and I'm amazed some still go this route. I had to get the builder on our last bungalow refurb to remove the plasterboard from the bathroom.