Cracked render for tiled wall - how bad is this?

Question

Hi guys,

Just finished grinding the plaster off the rendered brick walls for my bathroom renovation and noticed some areas have cracking of various sizes.

These walls will be tiled now so just wondering how much of a concern these are? Sorry for the bad pic quality, kind of hard to get a good photo given the lighting in there.

One or two areas sound a bit hollow when tapping, but it’s hard to tell for the others because they are on an external cavity wall.

If these cracks are cause for concern, what is the easiest way to chip the render off without damaging the surrounding solid render?

Nailbag · Answer

Hi @bigkid

It's impossible to identify the cause of the cracks. Initial thoughts is they are due to a thin inferior layer of render. At this stage you need to waterproof the bathroom. As with @R4addZ I would highly recommend getting a certified waterproofer to do the works. They will be able to determine if the waterproofing membrane is flexible enough over the cracks or need some form of repair.

The stage of waterproofing is the most critical in any wet area renovation. So its important not to cut corners and ensure its done to the very high standards now in place,

Nailbag

R4addZ · Answer

Hi @bigkid

The area needs to have a waterproof membrane applied and that has to be done professionally so get a waterproofer in for a quote and he will tell you whether he can do the job over the existing render or not!

JacobZ · Answer

Hi @bigkid,

The cracking does not appear too severe, but that kind of pattern can indicate that the render has shrunk, aged or started to lose its bond with the brickwork in places. The hollow-sounding areas are the greater concern, as they may suggest the render has partially separated from the wall.

The important point is that the tiles will only be as secure as the render they are bonded to. Even if the tile adhesive performs perfectly, any loose or poorly bonded render underneath could still detach from the brickwork and bring the tiles with it. Nothing in the photos appears to be actively flaking or failing, but it would be very difficult to make a confident assessment from images and tapping alone.

Before waterproofing or tiling, I would have the walls inspected by an experienced renderer. They can determine whether the cracks are stable and suitable to simply tile over, or whether sections of render need to be removed and reinstated. I note that you've previously had a plasterer/renderer out to assist with the bathroom you've been working on. They are likely the best person to speak to for an opinion.

If removal is required, the loose areas can be cut around with an angle grinder with a diamond blade such as this

https://www.bunnings.com.au/kango-125mm-turbo-diamond-saw-blade_p0069755

, and then chipped away using a small cold chisel and hammer.

Allow me to tag @R4addZ and @Nailbag to see what they think.

Jacob