Converted Barn, expected penetrating damp

[wa540]

:? I am hoping you can help. After a recent survey we have been informed that we have penetrating damp on some of the walls. The explaination is that the salts have built up from the urine from the previous occupants ie cows, and over the years the walls dry and the salts slowly migrate through the surface internally. As the plaster was not Salt restistant the insoluable salts come through the walls, probably being hyroscopic and giving the impression of rising damp.
We have been recommended to remove all the plaster, fix a impenetrable membrane to the wall, and whitewall plaster and skim.

As this is rather alot of mess and cost etc .. is their any other option open to me ?
May be remove the loose emulsion paint, then coat the walls in a sealant and then paint over this ? Or do I have any other options ?

Hope you can help ? [/b]

 

[RobT]

Hi Wa540,

assuming the ultimate aim is to avoid the cost & disturbance of replastering I would explore the characteristics of the Classidur range. See link for one possible option -
http://www.blackfriar.co.uk/print.asp?prodid=37

They also have a paint specifically for 'salt problems' which contains concrete therefore may lead to increased dampness in the wall as a whole.

regards

Rob

 

[Paul Hopper]

Hi

How old is the barn/cowshed?
what is it built of
how long have you inhabited it.
??
Do you know when it was plastered (roughly)
what plaster finish is it?

let me know if you can and I will try to make some sensible suggestions.

Paul Hopper

 

[Penners]

I'm worried about any suggestion that involves "sealing" the wall. If it's an old wall it is unlikely to have any dpc, and despite the cow pee explanation given to you, I suspect that some simple damp penetration is still quite possible/probable. So it seems to me that your best course of action would be to maximise the breathability of the wall.

So, in your shoes I think I would hack off the existing plaster, allow the wall to dry out and then replaster with lime.

However - I am not an expert in this and I'm hoping that someone more knowledgeable than me will confirm or argue with the logic of my suggestion.

Biff - what do you think?

 

[Mark]

Could I ask whats on the outside of the walls and what are they made of ?

ie brick/stone/cob, paint / render (what sort?)

has it been repointed or does it need repointing.

Are you in a particularly exposed spot ?

 

[biffvernon]

Yes, definitely.

I wouldn't do anything that involves 'sealing' or installing anything 'impenetrable'.

I don't know anything about the paint that Rob suggested but the Blackfriars website assures us that it has 'High Vapour Permeability' and is therefore a 'Good Thing'. I'd be interested to know what this 'solvent based' yet 'odourless' paint is made of.

Cow urine and bacon salting often feature large in the survey reports of old buildings in the countryside. I suspect some of it is founded more in mythology than chemistry.

The first approach must be to check for all the obvious sources of water ingress; rainwater goods, high outside ground levels, botched cement pointing etc. Then give the existing plaster a good brush down with a wire brush removing anything loose enough to be removed with fingers. Then add a skim of lime plaster on areas where it is too rough or missing, making sure that the old plaster in thoroughly wetted. Keep the building well ventilated and enjoy the summer.

 

[Gervase]

I'd echo Biff's advice - don't do anything that can't be undone (as in applying a sealant or cement-based compound). The 'salt leech' theory is often bandied about, but outside water seems far more likely.
With any old wall - particularly rubble stone - you need time; it can take three months or more for the fabric to dry once you've dealt with the cause. So proceed slowly, take Biff's advice and don't be tempted by promises of a quick fix.

 

[wa540]

8) Thanks for all the posting I have read with interest. To answer some of the questions :-

The Barn is built solely of Brick, and although built in the 1800's it was converted around 10 years ago. I understand that they did not use traditional cement to re-point the barn, or the salt resistant plaster. On the outside of the property you can see where the wall is damp which is well above the damp droof course around 4ft from the ground. Nothing obvious could be causing the moisture ie no plants, drains, etc.
We have owned the barn for 2 years and the salts were visible pretty soon, the visibility of damp is flaking/craking emulsion on the wall, and spotting colour effect. The damp meter reading is very high.

I understand that this construction type needs to breathe and although replastering in lime plaster might do the trick I do not want to have to redo the rooms again having to then use the "membrane" ie on suggestion the John Newlath 2000 that is used on old churches etc ...

Look forward to you commnts. Many thanks

 

[Penners]

they did not use traditional cement to re-point the barn

I'm a bit confused by this. Do you mean they didn't use traditional lime mortar, or they didn't use cement (ie: did use lime mortar)?

 

[wa540]

They used modern mortar, no lime

 

[Mark]

Whats the damp proof course ?

Are you sure there isnt anything to do with the roof / gutters causing a problem ? Seems odd that the outside wall is only damp 4 feet up - it isnt rendered is it? ?Just brick ?

 

[wa540]

No render, just very old 1800's brick, can see damp proof membrane, and injection damp course. All sound. Some repointing has been done recently by previous owner probably modern mortar. Gutters all sound and none on that wall anyway, no roof for another 3m up and all OK.

 

[Gervase]

can see damp proof membrane, and injection damp course. All sound.

Ah, therein could lie the problem. I have yet to see an injected damp course that didn't cause damp problems. In my experience they are a complete con and cause far more damage than ever they can cure, I'm afraid. It's very rare for the chemicals to form an effective DPC, and more often than not they simply leach out following the gravity via the voids in the wall, leaving plenty of untreated material to get damp. If you also have a memrane, then it's odds on that an awful lot of moisture is coming from under the floor slab and trying to make its way out - and that could be via your wall.
What sort of brickwork is it?

 

[wa540]

Thanks to all the subscribers. But in the end we got in an expert which has saved us a shed load of money.
The outcome is that the walls have been painted with normal emulsion which is not breathable. Need to strip this off and use a special emulsion.
As for the salts, well yes you can dry line the walls at a cost of thousand or just redecorate a little more often. Rub down and re-paint. Our plaster is still perfect underneath.
As it's not too bad we will go for the option.
My advise is get a independant surveyor and not a builder at the first instance.
Thanks for listening / reading

 

[Penners]

The outcome is that the walls have been painted with normal emulsion which is not breathable. Need to strip this off and use a special emulsion.
As for the salts, well yes you can dry line the walls at a cost of thousand or just redecorate a little more often. Rub down and re-paint. Our plaster is still perfect underneath.

Hmmm... I'm sorry to nag on about this, but I'm still concerned about your word "plaster". Just to be clear - are you saying that the brick wall is plastered internally and on top of the plaster is this non-breathable paint?

If so, what sort of plaster is it? If it's gypsum, then I really doubt whether taking off the impermeable paint and replacing it with "a special emulsion" is going to help. Even if the special emulsion is breathable, the gypsum plaster won't be, which negates the whole point of the paint change.

Or have I misunderstood?

 

[biffvernon]

Perhaps my comment on this thread is relevant.

 

[wa540]

Well the plaster is excellent beneath the paint, no mould, no damp, no problem at all. just some of the paint flakes off and gives a high moisture reading. Normal for this kind of structure.
So time will tell if the paint solves the problem.

 

[MDE]

I had a wall in one room where any paint would flake off (even "breathable" emulsion). I was advised that the room had been used as a larder (i.e. for salting bacon) and that the problem was salt in the wall. It certainly didn't appear damp. Anyway, whatever the cause, I decided that the solution was to remove the gypsum plaster (which came off quite easily) and re-plaster with lime, finishing with limewash. It seems to be working so far. Another wall in the same room was damp. We found three big leaks in the central heating system right under and adjacent to it. Here I've just removed the damaged (gypsum) plaster and replaced it with lime plaster.
In short, I think the solution is probably the same (i.e lime plaster) whatever the cause, but do double check for sources of water as they could cause other problems.

 

[wa540]

Just doulbe checked the survey and the plaster is sand & cement,