Corrugated tarpaper behind plaster on slightly damp wall?

[Adrian]

We've just moved, to a house with an old (early 18th century, probably) solid stone-built wing.

There's a couple of bits in the dining room and the wall separating it from the hallway, either on the external wall or very close to it, where the paint and plaster looked very suspicious. Paint slightly blistering, evidence of lots of patch-plastering in the past. You know the score...

So I ordered one of the cheap Silverline damp prong-and-buzz testers, which arrived this morning. Sho'nuff, bzzzt-flishy-flashy. Only in fairly localised areas. Outside, those areas have been piled high with earth, rotting-down vegetation, and various plants growing up the wall. So there's not a lot of doubt as to where any damp's coming from. It's all cleared off now. There's a few bits need repointing and repainting, but no real damage.

The floor is all tiled, presumably on a concrete base, with underfloor wet heating.

I've just hacked away at the wall - easy enough, with plenty of blown skim and patching in the past. Some of the "wet" bits gave no buzz once behind the paint and skim, others did more behind than on top.

The outside wall itself all sounded very hollow - and appears to have some kind of black corrugated tarboard or tarpaper behind it. I've not gone behind that (yet)...

WTF is it? Insulation? Damp-proofing? Useful or waste of time?

Pics:

What's the best bet for dealing with the wall itself?

[Jim K]

bodge?

Jim K

[Adrian]

Very likely...

[meow2222]

problem solved, probably

A poor attempt at dampproofing. It fails by stopping condensed water vapour reaching the outside & evaporating. Best removed.

NT

[harry]

You have a building with a common problem. Decorative finishes years ago were slightly porous so that and damp penetrating from outside could evaporate. Nowadays they blister and fall off.

Also humidity from cooking etc inside the building penetrates the structure and condenses within it. (Interstitial condensation). There are several possible solutions, most you can do yourself which depend on the detail of the building. External insulation is the first one to look at. However it is all a lot of work DIY or very expensive.

Or possibly, Look at "Green Deal", it might be the thing and someone will give you free advice.

[harry]

BTW. The "tarred paper" is an attempt at a vapour barrier to cure interstitial condensation. Sometimes effective sometimes not. Depends on how well the work was carried out.

There are moisture resistant/repellent cements you can use but this will not cure the inherent poor insulation of such a house.

Your moisture meter will tell you a wall is damp but not why. Could be penetrating/rising damp or condensation.

[Adrian]

As I said in the original post, the outside of the wall was piled high with earth & plants & leaf mulch & goop. It's a 300yo wall with no foundations and no "modern" DPC built in.

In addition, the house has been basically empty for several years, with just brief periods of occupation. It is basically very well insulated, though, with a LOT of work having been done in the last 15yrs.

It's not going to fall down tomorrow. Maybe the plaster and paint will mank up again, maybe it won't. Either way, I think we can take a reasonable guess at the cause.

Thanks all. I think I'm going to give it a week or two, with the outside of the wall cleared back, and see what happens. Then patch the bits I've attacked up, slap some paint around, with the expectation of ripping that wall back to bare stone and replastering from scratch in the mid-term future. When I've learnt how to plaster...

[fred]

Swmbo's parents moved into an old farmhouse about 40 odd years ago. Renovations included applying this treatment to the ground floor walls as an alternative to the non-existant damp proof course.

[meow2222]

Rising damp is rare. A somewhat insulating wall with a vapour barrier close to the outside is a recipe for damp. Rubbish piled against it ditto.

Heating helps a lot.

Such things usually take longer than that to dry out, but a couple of weeks of exposure will certainly help. If you've addressed the causes by clearing junk and removing the tarpaper, you may as well refinish.

NT

[Tim Watts]

On Tuesday 04 June 2013 08:39 Adrian wrote in uk.d-i-y:

Perhaps replacing the plaster on the affected wall(s) with lime plaster and then whitewashing might be a good approach - just allow the whole thing to breath?

[Martin Bonner]

or any other vapour permeable paint. Farrow and Ball casein distemper or Earthborn Claypaint both work well.

+1

[newshound]

It's to stop rising damp from evaporating, eventually giving you a saturated wall.

[Java Jive]

Although I've read some of the thread before, I just read the title as:

Corrugated taxpayer behind plaster ...

He should've taken the bods at the IR out to d [snip]