Preparation Triple boarded, old adhesive, heavy tiles!

[1animal1]

Hi all,

I have an issue I'm hoping you chaps can help me with after removing tiles from my en suite. The adhesive has partly come off, 30% probably (the rest will be a total pita), the issue i have is that I'm not sure i can lay straight over the old adhesive, even though it is only 2-3mm in depth? I would ordinarily try as it is level and fairly low profile, but best practice? My initial plan was to lightly skim given that i will be loading it with 600x300x10 porcelain (not bought yet) which has to be bordering on the 32kg limit per 1M2 (with grout and adhesive) for none skimmed wall board. I can't board over the existing board as it will narrow my soon to be shower unit too much below the 700mm width minimum, I can't easily remove the old board as the wall is made up of 3 boards dot and dabbed, which looks like 3x20mm boards, I've never seen that thickness plaster B's before!
I luckily only have 3 walls to do as I've dot and dabbed new 12.5mm board on the external wall, it is still 12sqm left though and i'm not sure the old adhesive will be removable....

Second problem is that one corner is out by about 11mm depth and is a bit inconsistent top to bottom - the rest of the wall is entirely square until you get to the last 300mm where it meets the external wall and goes away from you - again, I was going to use backing plaster and skim to make it level but that will give me the other issue of only 20kg weight bearing per 1M2 - any solutions? Tiles will be laid across and in parallel (not brick formation) following the lines of the floors 600x600 tiles, but when it hits this corner they will have to be cut to 400x300 so most of the weight will be on the rendered area....

I hope this all makes sense

Thanks in advance 🙂

Tim

 

[On one]

Take the 3x20mm boards off and install plasterboard onto timber studwork???

 

[1animal1]

That's not an option I'm afraid. The wall to the next room is this 3 board combo, no stud work at all.... But given they are 20mm boards I'm thinking they'll have much higher weight capacity than 12.5mm... If I can sort these out

 

[White Room]

It's the paper on the board face that takes the weight, not the board thickness.

 

[1animal1]

Ah ok, so ideally I need to remove the adhesive? If it's possible with a steamer perhaps.

What about the bit that needs building out?

 

[1animal1]

Is there any possibility of laying 600x300 porcelain on top of old sound shallow adhesive if its straight? or is this a terrible idea? (applying adhesive to the tile for uniformity).

 

[SJPurdy]

I have only come across this type of structure once before and maybe others may not be aware of it. It was the way internal walls were built in a neighbouring new property. A batten (guess) 20mm thick was fixed to both the floor and ceiling in line with the wall position. PB* was screw fixed (top and bottom only) to one side. 20mm PB, cut between the battens, was then glued to this first PB (can't remember what type of glue but think it was thin so probably not PB adhesive). This 20mm PB was the centre of the wall. Then the third PB* was fixed (glued) to the centre 20mm PB and battens. The wall is made up of just these three sheets of PB attached top and bottom only.
Wires were channelled into the centre PB I think.
*I thought these may have been 12.5mm but could have been 20mm. Sorry to be so uncertain but it was a while ago and I wasn't actually involved in the construction. I did tile the bathrooms with 20 x 20cm ceramic tiles (so not very heavy) and they are still standing (and admired!). I have often wondered what would happen if someone tried to retile them.

I do not know if this type of structure has been load tested/approved for tiling maybe someone else does.

Sorry Tim I don't have a solution. Even if you replaced the surface PB with eg. 20mm Wedi board (or similar) in my opinion it would still need mechanically fixing to something more structural than 2 sheets of PB.

 

[1animal1]

No worries SJ, thanks for the insight. I've not had one down yet so unable to clarify construction, other than its a 1986 build and they seem pretty sturdy with good sound insulation through the boards.... The tile store who I bought these porcelains off had tile fitters as the salesmen and they looked at me as though I'd just fell off a boat when I started talking about maximum weights on plaster and skim. Although having since spoken to a plasterer, he was convinced that if I use browning as opposed to bonding to build my corner out, I should be fine. I then stumbled upon some mapei cement based adhesive, so thought I'd be best laying a layer of that down as a 10mm base.... Cheaper with less waste than a 25kg bag of browning.

I'm going to borrow a decent steamer tomorrow to attempt lifting the old adhesive, figure if I can get down to the original paper, I'll stand half a chance...

 

[White Room]

No worries SJ, thanks for the insight. I've not had one down yet so unable to clarify construction, other than its a 1986 build and they seem pretty sturdy with good sound insulation through the boards.... The tile store who I bought these porcelains off had tile fitters as the salesmen and they looked at me as though I'd just fell off a boat when I started talking about maximum weights on plaster and skim. Although having since spoken to a plasterer, he was convinced that if I use browning as opposed to bonding to build my corner out, I should be fine. I then stumbled upon some mapei cement based adhesive, so thought I'd be best laying a layer of that down as a 10mm base.... Cheaper with less waste than a 25kg bag of browning.

I'm going to borrow a decent steamer tomorrow to attempt lifting the old adhesive, figure if I can get down to the original paper, I'll stand half a chance...

On plasterboard ?

 

[1animal1]

That's what he said which I questioned. Said it'd be stronger and would grip better to the board... I've only ever known browning to be used on direct blockwork