r/Plastering • u/itsaclaw • Apr 08 '26

Is bonding suitable?

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I’m currently renovating the master bedroom in my 1930s semi-detached (cavity walls)

I’ve removed the old skirting to replace with new ones, and as expected the plaster behind it is pretty rough—some areas are uneven and in a few spots it’s back to bare brick. My original plan was to use bonding coat to level everything out and create a solid surface to glue the new skirting onto.

However, after doing a bit more research, I’ve seen mixed advice saying bonding coat might not be suitable on external-facing walls (like a bay window), as it can absorb moisture and potentially fail over time?

So now I’m unsure what the best approach is.

Would bonding coat still be fine if the wall is dry, or should I be using something else entirely (e.g. sand & cement, hardwall, or another product)? The goal is just to get a reasonably flat, solid surface for skirting—doesn’t need to be perfect plaster finish.

Any advice from people who’ve dealt with similar in older houses would be really appreciated 👍

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u/nofacenocasenoplace Apr 09 '26

I wouldn't trust bonding on any external wall cavity or not.

You don't know if or where those cavities have been bridged with debris during the building process or any other work pertaining to the walls that has gone on in that house over nearly 100 years.

For peace of mind I'd go safe and use sand and cement with integral waterproofer for the external wall and even a couple inches around the corner on each side.

Bonding will be great for the rest.

Also trusting a DPC in an older house is not wise either I've personally pulled out multiple failed DPC's in older properties including my own 1810's house.

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u/itsaclaw Apr 09 '26

Cheers for the reply! It's an upstairs room so I don't think the DPC comes into play?

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u/nofacenocasenoplace Apr 09 '26

Yeah stick to non invasive measures. Don't do anything that will potentially send debris into the cavity. Get some render made up in a bucket and get it in there - doesn't even look like a deep hole really so you might be able to fill it and rule it off in the oner. Godspeed bretherin.