Crumbling wall behind plaster

[sherburn]

Knocked off a load of plaster to uncover damp stone walls, mortar crumbling quite severely. Just wondering if there's a chance knocking off more plaster could compromise the wall's structural integrity? The wall was solid before removing the plaster, no cracks/signs of movement. Here's a pic of the exposed stone:

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• sherburn
• 24 Oct 2011
• 1

The plan is to apply a damp proof membrane to the damp wall, so is the best approach to continue taking off all the loose plaster and re-pointing using a standard sand/lime/cement mix?

 

[sherburn]

No interest in that, looks like I'll probably have to get an expert in just to make sure I don't end up knocking the house then!

Not sure if this will generate any responses either, but do any of you know what this is? Very hard and dark, behind the plaster, haven't seen it before and I was wondering what it is, and why it would have been applied. Maybe something to do with the wall being damp?

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• sherburn
• 2 Nov 2011
• 1

 

[mointainwalker]

Plaster is not a load-bearing substance, so knocking it off should have no effect and even if a few stones fall out that won't make any difference in my experience.

Are you saying you want to cement-render then add an impervious membrane ?

What is the planned make-up of the finished wall ?

 

[sherburn]

Thank you, that's reassuring. Made sense that it'd be safe to carry on, but with it being the first time I've done this I don't want to take any risks!

The plan is to scrape out all the old crumbling mortar and re-point the wall, then I'll need to attach the membrane (yes, one of those dimpled impervious ones), so I'm not sure yet, but presume I'll need to apply a scratch coat first. It'll be naked membrane with a stud at the rear retaining wall for insulation, then meshed membrane around the other walls. Not too sure about the pictured wall yet, as it could do with some insulation, but there's not really the space for a stud. Need to do some research really, ideally would like a membrane that comprises a layer of insulation so it's easy to fit to the wall, but have no idea if that even exists, and if it does I'd guess it'll be expensive, and cost is a major factor!

 

[mointainwalker]

The plan is to scrape out all the old crumbling mortar and re-point the wall

OK, however with a wall like that I think you will scrape away the crumbly and then find some more........then some more. Think you need to be prepared for rebuilding a good bit of it.

Is it obvious why the wall is damp ? Cracked render outside, high outside ground-level ?

 

[sherburn]

Thanks, I'm hoping I'll be able to get away with just replacing the outermost regions- if a stone of two fall out, scrape away behind them but draw a line at going any further back than that, unless it's still really crumbly behind that, if that doesn't sound foolish?

The render outside has been replaced in the last few years, ground level is a foot or so higher than the inside, and apparently until around 6 months ago there was an air brick below ground level which was just acting as a drain- allowing water into the house beneath the wall whenever it rained! So while I expect there will always be some level of damp coming through, hopefully the membrane will help to keep levels below what they were before, and slow down the degradation of the existing mortar.