Damp Interior Wall - Is this the right course of action?

[Jill]

An interior wall in our stone cottage for some reason was never damp proofed when it was renovated 20 years ago. The wall in question is 22" thick. The wall clearly has some kind of damp problem as the lower third of the wall paper was a different colour to the top, (made more obvious with 20 years of Pauls nicotine on it).

From what we have read from various sources we believe that the only way of remedying this problem is to strip the wallpaper (already done) paint layer, plaster and cement/sand render to expose the stone wall? Paul would like to retain the stone wall as a feature but this will depend upon the stone. Any render/pointing should then be done with some kind of lime mortar to allow the wall to breath? I don't know what is between the stones but the house was built circa 1700 if not before.

Earlier in the year I did a test square (behind the sofa) so we could discover what was going on inside the wall, the cement/sand render seems dry and it was at the time of chiselling, and the stone was dry. It is just the plaster that seems to be the problem. Is this right or is the cement/sand the problem as well? This is about 2" thick. I spoke with Pauls brother who put the cement/sand render on originally and he said this was the correct mix as it was thought that the wall had been injected.

I know that getting rid of the render is going to be hard work but if this will stop the problem being so visible surely it will be worth it?

We also have a few damp patches on the outer walls in the same room where we believe the damp proofing stuff which was injected hasn't gone into all of the crevices. Any suggestions on what we could do with this to stop it showing on any wall finish that we decide to put on in future, it is currently wall papered but we are thinking of doing something else but what we haven't decided yet.

 

[biffvernon]

It is very unlikely that even if someone had tried injecting anything into a 22 inch thick stone wall it will have done anything useful.

The stones of a pre-1700 wall may have been mortared with lime or just earth, but definitely not Portland cement.

Certainly remove the wallpaper, paint and plaster. If the cement render is firmly attached it might just not be worth the effort of removing it even though this is desirable. Making a feature out of the bare stone is a rather 21st century fad and not what would have been done originally. It would have had a clay or lime plaster, painted with limewash or distemper. Returning to such materials will probably solve the damp problem.

If the cement render stays, then putting lime plaster over it may well also solve the problem. It is likely that the source of moisture was from condensation of water vapour in the room on the relatively cool lower part of the wall rather than 'rising damp'. This is not good for gypsum plaster, but lime plaster will just absorb the moisture harmlessly and return it to the air when the relative humidity drops.

 

[NT]

Not a lot I can add to that, pretty much all been said.

Think what happens to this wall. First its sitting on wet soil, and is likely to contain earth as mortar. Even if originally built with lime, it may now be earth filled due to 300 years of decay, dead insects and so on. Stone has poor insulatoin, and the ground will be below ambient temp, hence condensation on the lower part of the wall is no surprise. Now if the render is anything less than perfectly impermeable it will have rain soakage too.

So its a wall with at least 2 or 3 sources of water. Which is going to keep such a thing drier, a waterproof outer coat or allowing the damp to evaporate out? When impremeable renders are removed these walls tend to slowly dry out with no further action.


NT

 

[Jill]

Thanks for the replies.

Although we have decided that the best course of action is to remove the render which Biff agrees is the most desirable option I think we are best doing it in stages, remove the plaster next to see if the render is dry and then if absolutely necessary tackle the render. (I'll offer to do the plaster,the easiest bit, then play the pathetic woman and pass the job over to Paul) only joking I'm not afraid of some hard work, however long it takes. As i've said before rush and Paul don't go together.

Biff do you think you will still have your Oak business in 5 - 10 years time? Being in Lincolnshire aswell we would much rather source our materials locally if possible, (Don't rush to get your order book out yet though, we have along way to go before we reach that stage)

 

[biffvernon]

I'll lay down some timber to get it well seasoned for you

If the moisture had come from condensation then when you take the plaster off you may find the render is quite dry. Put gypsum plaster back and the problem may return. Put lime plaster back and it probably won't as lime is much better at absorbing and releasing moisture without damage.