Alcove Shower Refit - water damage to chipboard floor, stud walls & plasterboard

First post

I'm having to refit a first floor shower alcove in a 20 year old house that has suffered water damage from the shower to the floorboards & stud wall. Construction is 22mm V313 MR chipboard floor on treated 9x2 timber joists at 600 centres with the 1000x800 alcove formed of regular 4x2 CLS studwork finished with 12.5mm MR plasterboard. The existing 250x200 ceramic tiles need to be retained or the job will get out of hand if I end up retiling the whole bathroom.

I'm planning to replace the flooring with No More Ply 22mm boards to the whole room (about 4 sq.m.) and I thought it would be good to fix some treated 4x2 CLS noggings between the joists beneath the T&G joints of the NMP. Joists are in good condition. I then intend to rebuild the lower sections of the alcove stud walls with pressure treated 4x2 CLS and replace the lower section of plasterboards with 12/12.5mm tile backing board to around 600mm above floor level, keeping the existing plasterboards and ceramic tiles from 600mm to ceiling as they're in good condition and have not suffered the water ingress of the lower sections. I'll also fit a new low profile (40mm) shower tray to replace the original which was 95mm tall. This means a fresh course of (taller) tiles directly above the tray - I think I'll have enough spares to complete this - fingers crossed

My plan is to tank all the new boards and I would appreciate advice from the experts here on what materials to use for this and how to make the join between the new tile backing boards and the existing plasterboard at 600mm above floor level?
I would also welcome any advice on sealing the new tray to the alcove walls. The tray will sit directly on the new NMP floor with the waste outlet running between the joists.

Thanks in advance

Hi and welcome to the forum!

It's great having new members around. How are you getting on with your job? Have you got any photos?

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If I use a tile backing board over the 22mm NMP flooring, is it advisable to cover the whole floor, including the area underneath the shower tray?

Is any further information required?

Are my posts visible to other forum members?

Yes they're visible. Unfortunately I can't help with your questions other than to say that If you use a waterproof board such as Wedi, Marmox, Schluter etc, you won't have to tank it. Where it meets plasterboard I would tape the joint.
Personally speaking, were it my shower - bearing in mind the failure it has suffered - I'd rip the lot out and start again with a proper tanked installation. Who knows what damage there is behind those tiles..

Thanks Steve,
I had thought of reboarding it all, but that would mean retiring the whole room, which is a job too far at the moment. I have also thought of reboarding & retiling just the shower alcove for now and stocking up with enough tiles to do the rest of the room at some future time, or even having a new contrasting set of tiles in the shower alcove to the originals in the rest of the room. This may happen, depending on how my enthusiasm levels are when I've got the new floor laid! I don't really like my plan to just reboard the lower section, but the rest of the structure does look sound from what I can see in the stud wall cavity.

I would just use 12.5mm PB again and they tank with a paste solution, mapei , weber etc do suitable ones. Tape all internal joints. Then install the tray and fully Silicon tray in. Then its all tanked behind and below the tray. Tile and Silicon internal edges and tile to tray edge.

I've re-laid the floor in 22mm No More Ply and have decided to remove all the tiles and plasterboard in the shower alcove. I'll replace the plasterboard walling with 12mm No More Ply boards and apply a brush-on tanking barrier over the whole floor below the tray and the new shower alcove walls.
What tanking is recommended to paint over the new NMP walls & floor please and also, what tape to use at the joint between the walls/floor and in the wall corners?
Thanks in advance
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Anyone?

Lots of tanking options available, mapei, Ardex, purigum, etc all good , from those my personal choice would be Ardex WPC. Tanking kit.

Thanks Bond.

Is the Ardex WPC ok to use as a tanking membrane to the floor under the shower tray?

Absolutely.👌