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moisture on inside walls of old stone house

We spent 14 years restoring an 1820s stone house. The plaster was off in some parts of the house. In an area that still contained the brown coat and scratch coat we added a thin layer of drywall compound since we have no plasterers in our area. In 5 years time it had started to bubble(for lack of a better word). It has progressively gotten worse. The double stone walls are 24" deep with an air space between withe the plaster adhered directly to the stone. The worse part that is bubbling is below grade but we had installed a french drain at the footer.
We are going to have to remove the drywall compound and probably part of the brown and scratch coat to see if we can figure out what is causing the problem. Is there anyone who has a similar problem and how did you fix it?
We cannot stud and drywall that area since it has chair rail, a fireplace and a communion cupboard.
My husband suspects that through time something has filled the air space between the walls and is causing the moisture to wick through.
Is there anyone who can help?

Re: moisture on inside walls of old stone house

How sure are you that there's an air space between the stone walls? Air spaces are common with today's curtain walls, but I'm not sure in the 1820's if that was a consideration. They were probably more concerned with strength and the walls would be tied together.
Plaster chemically hardens sort of like concrete and is somewhat resistant to moisture.
Drywall compound may dry hard, but it will turn soft if wet again.
I suspect the drywall compound is being subject to moisture and eventually bubbles.
Try to see if water is getting into the wall from outside. Typical places are at windows, flashing, chimneys,ledges, etc.
Its possible the mortar between the stones needs repointing. I also don't know what if any waterproofing is recommended for old stone walls. A contractor/Mason specializing in old stone restoration could be a good source of information.
Moisture could also just be from normal condensation in a stone wall that the drywall compound can't handle or stay stuck to the substrate.
Ps. Plaster isn't that hard to work with.

Re: moisture on inside walls of old stone house

Thank you for your quick reply. We agree with you that the dry wall compound is retaining moisture and that is the cause of the bubbling. We are 100% sure there is an air space between the walls since we had to take all window and door frames out to square them before putting in new ones. I'm sure there are stones tying the two walls together.
This is a two story stone house that has been completely repointed and has a new roof. There are no windows in the vicinity of the area with the moisture problem. It is all below the chair railing.
We have never used any product like dryloc but were considering removing the area in question and possibly removing a couple stones to clean the air space then coating it with dryloc, but are not sure we can get anything to adhere to the dryloc surface.
You said plastering is not hard to do. We have taught ourselves to do a lot of things while restoring this house so probably could tackle that too. Can you tell me if the product referred to as patching plaster has the same qualities as regular plaster or is it going to draw moisture also? The area in question is about 3'x8'.
Thank you.

Re: moisture on inside walls of old stone house

I don't know if "patching plaster" is the same as plaster. I suspect it is. Look at the package and see what it is made of. It should say plaster of paris. It might have modifiers in it help it adhere to the substrate. Since the rest of the wall seems to be okay I wouldn't put anything below the patch. Be sure to prep the surface to get off any compound. And score what's below so the patch has something to key into. A 3'x8' area shouldn't be too hard to patch. You'll almost be a plasterer by the time your done.
Ps. I'm not so sure the old patch drew moisure, but rather the drywall compound reacted poorly to the moisture in the wall.

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