Dot and Dab Double Skin

[pertinky]

Hey guys,

Quick question regarding wall prep for tiles (porcelain most likely roughly 600x300) ...

Ive got 2 internal and 2 external walls, 1 of the internal/external walls have been taken back to brick as the bonding coat was coming off in large peices and a shower will be fitted in the corner where the external/internal walls meet.

The other two walls I have removed tiles and left some patchy bonding/skim (skim below old bath and bonding above). Seems in good nick although there are channels that need filling around 20mm deep where old pipe work has been chased out back to the brickwork.

The room is woefully out of square with one of the bonded walls bowing terribly but we are fitting a bath against this wall (quite possibly 25mm+ out by the end of the bath although it bows back in towards the other end).

The walls are 9 inch double skin brickwork with a small gap in between (10-15mm).

Ideally, I'd like to square up the room and was wondering if its possible to D&D the external walls when its double skin.

This would mean taking the other two walls back to brick too but they are only half height as we're up in the eaves. The plan is to tile up to the eaves on the external walls and up to the full height on the internal walls.

 

[pertinky]

Oh, I wont be using PB in shower/bath areas btw!

 

[23vc]

Yes you can dot and dab, be aware that strictly (eg if building regs are involved) if you take an external wall back to brick, you’re also meant to bring the insulation up to spec ie some degree of insulation if it’s an uninsulated 9inch wall for example

 

[pertinky]

I guess in this context its on a best effort basis of what is reasonable.

Not alot of room in a bathroom/ensuite to put anything more than the 22mm insulated plasterboards really. Although Part of the wall (50%) would have tile backer board which wouldnt be insulated unless you can stuff some polystyrene behind it

What about using Marmox insulated boards instead? would kill two birds with one stone without loosing too much out of the room

https://www.pureadhesion.co.uk/marmox-1250x600x10mm-insulated-tile-backer-boards.html

Edit: I would still need to give a finish coat to the boards bringing it to probably about 12-13mm. This doesnt help me in the shower area though unless I can classify it as "tanked" due to the boards behind the plaster being virtually waterproof.

Another edit: Once fitted, Marmox Multiboard can be tiled or plastered on to immediately. So no need to plaster which is great! I'll need to use the fixing dowels though so I can straighten the walls out.

 

[23vc]

It’s only if building regs are involved, if not no ones going to know so crack on

 

[pertinky]

I had a chat to Stratford BC. As we're splitting bathroom in to bathroom/ensuite, the ensuite will be notifiable, but the bathroom would not be as the layout isnt changing we're just chopping off the rather large airing cupboard at the end to create the ensuite.

I'm only doing the bathroom at the moment and plan to do the ensuite in September.

They are happy as long as Marmox has got BBA certification, which it does.

Its only a small area in the bathroom that needs straightening up once the new stud partition is up, about 2m long x 1.5m height so it might be worth grabbing a few boards and fixings and testing it out for the sake of a few extra quid. At worst it will provide better insulation and a flat tiling surface and should be fairly quick to install.

I can probably leave the walls as is, and just take it back to brick where at the corners/center of the boards where the fixings will be to save making a mess again