Hi,
we are renovating a shower room in the basement and I need some advice before proceeding.
Background: house from the late 70s, interior insulated basement. The shower room is part of the laundry room, with a simple partition wall between the laundry room and the shower room. Size of the shower room about 160x385. I guess it was meant to be a sauna in part of the shower room but it never was. The room is located in the corner of the house. A small part of the room has been a "wet zone" with a waterproof mat on the walls and floor (the red line on the picture indicates the waterproof mat. Other walls are untreated gypsum board.
We will have roughly the same layout as before, with a mat on the walls in the shower, but painted fabric in the rest of the room.
I have removed the mat from the walls and also taken down the small partition wall E (which will be replaced with a glass wall). Much of the paper on the gypsum came off when I removed the mat, so I took down the gypsum boards A, B2, and C. Board B1 also has poor paper, but cannot be removed as it continues into the laundry room, behind the partition wall. The floor installer said it would not be a problem that the paper is loose, they will prime and putty, so I trust it will be fine.
But now it occurred to me that I probably want OSB/plywood behind the new gypsum boards to attach shower walls and such. There are some old noggins for the shower mixer, but that's all.
How do I solve this in the best way?
My suggestion is to put 12 mm plywood where gypsum board B2 and C were. Then put new gypsum on top of this. I then need to offset the joints, so that I don't get plywood and gypsum joints over the same stud. This will lead to two gypsum joints in the shower, over stud R2 and R3.
Some questions arise:
- Can you place 12 mm plywood edge to edge with a gypsum board and then put a layer of gypsum on top without the thickness difference being noticeable (gypsum is 13 mm)?
- Is it a problem that the joints on the gypsum will be in the middle of the shower (over studs R2 and R3)?
- How do you deal with the outer layer of gypsum over board B1? There is no stud in the corner that I can attach the outer board to. Is it enough to attach to the floor/ceiling? Or should I glue it in some way? If so, with what? Gypsum putty?
The nice thing about plyfa behind gypsum is that you can have the gypsum seams wherever you want. Regarding gypsum without corner studs (b1); remove everything loose, prime, then use construction adhesive that works well with gypsum board. Tension the board while the adhesive cures.
