How can we make these internal/external walls 100% Waterproof for new En Suite?

FrankFalcon

Hi guys

We are renovating a really small, old terraced house. We knew when we bought it that all the (plaster & lath) ceilings would have to come down and all the walls would have to be stripped of the loose plaster. So, over the last few weeks we have done exactly as that, and we now have every wall stripped of plaster and looking exactly like the one shown in the image. The next stop in the whole house is first fix electrics and plumbing, (which we will get professional tradesmen in to do), but we are stuck what to do on 2 of the walls that are stripped back to brick because we want to make a new en-suite bathroom. Please look at my bad drawing of our intended en-suite bathroom. The long back wall is an external wall. The 90 degree wall to the right is also an external wall. Both these walls are not shared with another house. Rain, literally hits these external walls! The left wall is a stud wall and the front wall is a stud wall. So, because we want to make this room an En-Suite bathroom we want all walls to be 100% waterproof. On the stud walls we know we can screw Waterproof cement board (brand name Aquapanel) to the walls. However, with the two external walls we don’t know what to do. We can’t dot and dab the cement board to the walls because the nature and the features of the cement board mean that dry wall adhesive doesn’t stick well to these boards. We don’t want to wooden batten the walls (and then subsequently screw the cement boards to the battens) because we are really tight on space in creating this en-suite in a terraced house bedroom (and we think using battens, then these boards will add on around 80mm (taking into account that the walls are not square). In an ideal world on these 2 external walls we would just dot and dab these waterproof boards to the brick walls (with plaster now removed) but as I said, these cement boards are designed to be screwed to stud walls not glued to brick walls. Has anybody ever faced this problem? 

PS., I know some people will ask me why I want to use cement board but I have seen evidence before a few times… in a shower cubicle, over the years, where a bit of tile grout has died or water somehow has got into the standard plasterboard fitted behind tiles, it’s not long until the plasterboard gets soaked and fails and the tiles start to fall off. Any ideas guys? 

flashg67

Does the toilet external wall need to be fully waterproof? If not, consider plaster only (and maybe tiles) Battens and insulation behind the panels sounds a good option. Avoid using sealants if possible - solid walls need to breath, and ideally any plaster would be lime-based