Preparing walls for porcelain tiles

[stratford_noob]

Hello,
I would start wit ha little back story. We've both a house where the main bathroom begged for renovation, however we didn't have the dime, so we've decided to get it slowly. The bathroom was half tiles and half wallpaper. In the supper I've removed the wallpaper, re-skimmed the walls and painted, however although we have though that would be enough for now, we have just decided to redo the rest completely whilst keeping newly skimmed walls where possible. As we don't want to cover whole wall in tiles, the best size match were tiles 300x600 for our purposes, and we got some in porcelain with 7.4mm thickness. As the porcelain tiles are heavier then ceramic I have couple of questions to ask/solve. (pictures of the walls are at the bottom)

Walls
The bathroom has two plaster board walls and two brickwall with plaster. After taking down the tiles from the plasterboard the paper is obviously torn, The damage isn't deep though, so I'm not sure if this surface is sufficient for tailing or not. As far as I understand my options are:
- clear torn paper and tile over it
- clear the paper, seal/bond and then tile
- cut the damaged plasterboard and replace with new one
Similar questions are for the brickwall, as there is plaster on them. It seems to be in good shape, however as the plaster according to standards should hold only 20kg/m2 I'm not sure I can tile with porcelain tiles over it. So what I can do is:
- keep the plaster on and tile over it
- remove the plaster on the places where I want the tiles and place plasterboards directly to the brickwall and tile over it.

Adhesive
- I've picked Mapei Adesilex P9, is that the right choice?
- I'm not sure with the trowel size though.

Thank you very much for any advice.

Here are the photos of the current state (the walls still need cleaning form the old adhesive )

 

[Boggs]

I would be looking to cut out and replace the damaged plasterboard, but just check that it’s not paramount board (plasterboard with cardboard in the middle).
Although this can still be achieved it’s just a bit more involved.

As for the plastered walls you are going to be over the recommended weight of plaster with the porcelain tiles but not by a huge amount
and if it’s only half height tiling maybe worth scraping back, priming and tiling.

The other option is to take it back to brick/block and overboarding with 6mm backer board and fixing with screws and washers as below.

 

[stratford_noob]

Hi @Boggs , thank you for your reply.
I have decided to go with the plasterboard cutting and removing the plaster. Today I have finally removed everything from the bathroom and as I proceeded to looks what the plasterboard is, it turned out it is paramount board of course. What is the best way to proceed then? Still cut it, remove just one side and then build wooden frame inside to put the regular plaster board onto it? Or maybe not to tile over it and try to skim and paint it? although some parts are above bath, so that would still need tiling I believe.

 

[Boggs]

I thought it would be.
Remove the damaged board and scrape out the cardboard middle, I use the claw of my hammer for this, and build a frame using 3x2 CLS timber and fix new board to this.

 

[stratford_noob]

Thanks again @Boggs .

Should I scrape whole of the middle cardboard or just columns and rows I will be putting the frame? One wall has a bedroom on the other side, so I wonder if the other side plasterboard will still be sound after removal of the middle. Should I gripfill the frame to the other-side plasterboard also? Fill the cavity with insulation?

I'm sorry I have so many questions.
[automerge]1573507062[/automerge]
Also, the cavity is 40mm deep, so I believe I have to use 38x63mm timber to fir in there. I hope that would be enough

 

[Boggs]

I normally use Ct1 or Sticks Like to bond timber to the existing plasterboard, not a fan of gripfill personally.
38 x 63 cls is the size you need.
I take out all the cardboard and add some insulation.

 

[stratford_noob]

Thanks @Boggs .
I have hopefully last question. In the wall there are already existing studs. I suppose removing them is not a good idea as the would contribute to stability of the new frames.

However I'm not clear how to do the new frame then. I can think of two options:
- make new frame only from top and bottom + some middle studs, and use existing studs to close the frame.

- make the new frame as complete structure and then just screw the the sides to existing studs

 

[Boggs]

Yes, leave the existing timbers in place and build round them as your first diagram.

 

[stratford_noob]

Thanks @Boggs .
I'm afraid I have another questions 🤦‍♂️

I have removed the parts of the paramount wall where I want to put tiles and also got rid of the plaster on the walls.

Right now I still have little bit of plasterboard on the paramount wall that goes into the door frame.:

• what would be the best way to get rid of it? Or should I just keep it and match the new boards to it?
• you have mentioned 6mm backer board as plaster replacement. But the thickness of the plaster in my case is around 12-15mm, so is the goal to get thicker backer board to even out the surface with the parts of the wall I haven't touched? Or should I go with thinner backer board and than put something between the wall and the board to easily even out brick wall unevenness?
• Is there any reason not to put backer board also on the paramount wall or there has to be the plasterboard?
• The vent pipe box is plasterboard with plaster on top. Should I cut it and rebuild it with new plasterboard/backerboard or it is so small it does't deserve the attention?
  
  

thank you very much for your help!

 

[Boggs]

I think I would leave the plasterboard edges as they are and fix a timber in to hold the two edges together.
6mm backerboards should be fine, you will need to dot and dab them in place and then screw fix them when adhesive has set.
There’s no reason why you can’t use backer board in place of plasterboard, just be aware of stud spacing as they differ from plasterboard.
For the small extra effort I would definitely replace the soil boxing plasterboard.