Render Failed - what now?

[sws]

Hi all - thanks in advance for any advice you can offer.
I'm currently ripping out a bathroom and have found a problem with the wall behind the old shower. It is thermalite block to which about 20mm of sand/cement render has been applied when built. It has clearly failed in the areas I've removed, but I think is more solid above the door and potentially towards the stud wall (see photos). My intention initially was just to get the whole room skimmed (a dark art I will never understand so was going to get someone in to do that in a day), but now looks like I need to make the wall good. Few questions if that's ok?

Should I strip the whole lot back to the thermalite (upto the red line on the image above the door) and dot/dab or could I patch the failed area if the render is sound elsewhere?

If patching - what should I use?

If D+D, I'll obviously need to match up to remaining render so would that work (approx 20mm depth)

There is a shower going in that corner so presumably MR plasterboard. Ideally I'd use aquapanel under the area to be tiled but am I correct it can't be dot and dabbed and would it lead to issues with 3 different substrates on the same wall?

Any advice gratefully received.

 

[Monkey Boy]

Hack it all off then address cracked block work issue

 

[Danny]

Hi all - thanks in advance for any advice you can offer.
I'm currently ripping out a bathroom and have found a problem with the wall behind the old shower. It is thermalite block to which about 20mm of sand/cement render has been applied when built. It has clearly failed in the areas I've removed, but I think is more solid above the door and potentially towards the stud wall (see photos). My intention initially was just to get the whole room skimmed (a dark art I will never understand so was going to get someone in to do that in a day), but now looks like I need to make the wall good. Few questions if that's ok?

Should I strip the whole lot back to the thermalite (upto the red line on the image above the door) and dot/dab or could I patch the failed area if the render is sound elsewhere?

If patching - what should I use?

If D+D, I'll obviously need to match up to remaining render so would that work (approx 20mm depth)

There is a shower going in that corner so presumably MR plasterboard. Ideally I'd use aquapanel under the area to be tiled but am I correct it can't be dot and dabbed and would it lead to issues with 3 different substrates on the same wall?

Any advice gratefully received.

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as @Monkey Boy says get the render off and so you can see whats going on with the block work....

The “90-degree rule” refers to the angle of the crack in relation to the wall or opening (like windows and doors). Here’s how it generally works:

• Cracks running at 45 degrees (diagonally from the corners of doors or windows) often suggest structural movement, such as foundation settlement or heave.
• Cracks running vertically or horizontally (close to 90 degrees to the ground or to the wall) are less likely to indicate structural movement and are often caused by thermal expansion, shrinkage, or minor settlement.

So, in short:

If the crack is roughly at 90° (vertical or horizontal), it’s often cosmetic.
If it’s diagonal (around 45°), it could be structural.

This isn’t an exact science — just a rule of thumb surveyors use before investigating further (for example, with a crack monitor gauge or structural engineer’s assessment).

yep I stole that from AI.. but may help

 

[sws]

Thanks both. Think I’d come round to the idea of knocking most of it off. I suspect the blockwork will be fine. It’s thermalite stuff which seems to crack as soon as you look at it. It’s a non-structural wall and we’ve had a few of these crack in a similar way upstairs presumably through settlement and the massive render layer in places.
If I do hack it off, what’s best to replace it? I need to tie into either an area where render is sound (eg above the door frame) or into the 45 degree angle wall to the left (by the yellow line). It’s 15-20mm deep overall
Aqualpanel and green plasterboard?

 

[sws]

UPDATE.........
Hi. Well the render seems to have been holding itself up! Peeled of like a banana skin. Was really thick on this wall (presumably to make up to the doorframe. Blockwork looks ok apart from the odd cracked thermalite block which I think is just what they do. My plan now is to overboard with a combination of aquapanel (where the shower will be) and green plasterboard. Be nice to keep to roughly the level of the doorframe so was thinking of using PU foam (with some mechanical fixings for the aquapanel as well).
Any thoughts on how i should but together the aquapanel and plasterboard? Silicone?
Also I was thinking about using the taper on the plasterboard to butt up to the existing wall on the left (which is at 45 degrees) - will that help the plasterer out when he comes to skin, or doesn't it matter? Any other advice?
Thanks again!