Damp in stone barn conversion

[sharpener]

Last autumn we bought a conversion of two stone barns in Devon, with two known damp issues. The surveyor who specialises in old buildings said of them:

1. Gable end wall in first floor bedroom: no obvious cause, may need dry lining with a ventilated space behind

2. Cross wall in living room: minor problem, can leave untreated but monitor for evidence of spreading to nearby joinery. (This was originally an exterior wall but since 1882 has been internal between the two barns. Both walls are random stone ~18 in. thick.)

In both cases the problem is evidenced by flaking of the emulsion paint applied by the previous owners (and in the bedroom also efflorescence through the paint) which has become much worse over the winter.

The conversion was done by the previous owners in 1995 including an injection dpc to the internal wall (but not the gable end). The original contractors have ceased trading once and now want £200 for a re-survey before they will consider a warranty claim. We have been quoted by someone else for a Triton cavity membrane system with plasterboard over steel studding in the bedroom (penetrating damp) and injecting a cream-based dpc and replastering both sides downstairs (rising damp).

I am concerned that upstairs there is no drainage or ventilation proposed for the cavity and this may result in rot to the flooring timbers. Downstairs I am wondering whether a new attempt at a chemical dpc will be any more successful than before and what the alternatives might be. Hacking off and replastering will be extremely disruptive because the underfloor heating manifolds and other plumbing are boxed in on the wall.

We are also considering fitting a whole-house MVHR system and I am wondering if it would be better to do this first and then re-assess the damp?

 

[MdB]

Before you do anything, work out why you have damp. Downstairs, what is the outside floor level relative to inside? Can you lower the outside floor level? Upstairs, what is the outside of the wall like, any roof leaks etc? Oh and read the damp FAQ.

 

[Nemesis]

The original contractors have ceased trading once and now want £200 for a re-survey before they will consider a warranty claim.

A yes - a common ploy, and you'll probably find they won't find that it was their fault anyhow. But they will have pocketed the two hundred quid, given you some test 'results', and may be able to flog you more of the same.

If this sort of treatment didn't work once, I doubt it will work again, and any sort of injection will require replastering probably with a waterproofing additive.

My suggestion would be to see if there is any cause of damp you can find, and if not call in a genuine period buildings specialist (who will probably recommend hacking off modern finishes and replastering with lime and painting with a breathable paint).

As far as the gable goes - what is the pointing like, is it lime and sound?

 

[chuckey]

Gable end wall, has this got a chimney flue within it, what sort of stone are the walls made out of - some are permeable! Is the pointing intact? Does the gable end wall rise into the loft and if so, what is the damp situation?
If the damp FAQs have been attended to, dosing the wall with a silicon water proofer does seem to work but needs to done every couple of years or so. I have this problem too.
Frank

 

[Nemesis]

Please don't dose the wall with silicon.

Very bad idea indeed.

 

[chuckey]

"Cross wall", in my cottage this is a rock'n rubble wall with a sort of cavity, and as a big draught occurs when you remove a stone from it, suggests that its cavity is linked to the external cavity via some dodgy stonework. So it might be so in your case, the question is then, could the dampness in this wall be due to water percolating down (and inwards) from the outer walls, or is it at the bottom of the wall "rising damp".
Frank

 

[chuckey]

And why is it a bad idea?
Frank

 

[Nemesis]

Well, it's one of those short term things which can make matters worse in the long term. It's pretty irreversible too. Soaking stone in gunge isn't a great plan. It can trap more moisture in the walls.

But conservative repair isn't totally your thing is it?

The damp may not of course be penetrating through stone - it could be condensation, it could be duff pointing, and these things need to be looked at.

Apart from the bit about cement with lime for pointing (omit cement) this isn't a bad guide:

http://www.bradford.gov.uk/NR/rdonlyres/78842480-8614-4D04-8ABE-F21315D3713E/0/StoneElevations.pdf

 

[chuckey]

"its pretty irreversible" I wish it was!, so you obviously have not used any because the amount that is used is very very small, i.e. 5 litres did 8m X 5m of frontage and at least 1/3 of that ended up on the floor. Doing the maths, 5 litres = .005 Cu m. therefore 40 X thickness = .005 therefore thickness = .005/40 m or .5/40 cm or 5/40 mm = .125mm or .005 inches- twice the thickness of one of your hairs or half the thickness of a piece of postcard!! The good thing about it is that is displaces water and runs of impermeable surfaces so it goes where its needed.
"Soaking stone in gunge", can you be more specific about this "gunge"? I would tend to agree with you on this one, but then its all down to what this "gunge" is and what its meant to do.
It cannot trap moisture vapour and ordinary changes of temperature will cause any free water to turn to water vapour which will makes its way out, via vapour pressure.
Frank

 

[Nemesis]

My advice to anyone - and I think you will find most involved with conservation of period buildings would agree - is don't use it. As that link I posted also says.

If in doubt, call the SPAB technical advice line. Free.

 

[Gareth Hughes]

"its pretty irreversible" I wish it was!, so you obviously have not used any because the amount that is used is very very small, i.e. 5 litres did 8m X 5m of frontage and at least 1/3 of that ended up on the floor. Doing the maths, 5 litres = .005 Cu m. therefore 40 X thickness = .005 therefore thickness = .005/40 m or .5/40 cm or 5/40 mm = .125mm or .005 inches- twice the thickness of one of your hairs or half the thickness of a piece of postcard!! The good thing about it is that is displaces water and runs of impermeable surfaces so it goes where its needed.
"Soaking stone in gunge", can you be more specific about this "gunge"? I would tend to agree with you on this one, but then its all down to what this "gunge" is and what its meant to do.
It cannot trap moisture vapour and ordinary changes of temperature will cause any free water to turn to water vapour which will makes its way out, via vapour pressure.
Frank

Well, by your calculation it's so thin as to have, effectively, no effect.

It's generally accepted by people who know about these things (by which I don't just - or necessarily even - mean Nemesis) that this type of treatment is, at best, useless, and at worst, permanently damaging.

It's the modern material equivalent of the old SPABbers shibboleth, limewatering, with its magic ability to "mend" stone.

 

[sharpener]

Thanks for your help. In answer to the various queries:

The gable end wall is random laid in the soft local Devon red stone which cleaves easily; the pointing is in fair condition having apparently been repaired (?with a hard mix) at the time of the conversion. It does not have a chimney and the downpipes are sound. However the aspect is W and the eaves overhang is not very large; the wall is sheltered to some extent by the adjoining house ~5m away but this also keeps the sun off. The roof was new in 1995 and is in excellent condition, there is no smell of damp in the loft void (which is ventilated). I had initially thought there might be splashing from the TV aerial mast at the top of this wall but the damp is now too widespread for that to be plausible. We do not know the condition inside at ground level as it is covered by kitchen tiles.

Assuming some form of dry lining is required here, as recommeded by the specialist surveyor (as well as the damp proofing contractors!) on the grounds that the interior finish is not allowing the wall to breathe, I would particularly appreciate suggestions as to its construction and the insulation/ventilation/drainage of the void. Also whether the proposed ventilation with heat recovery is likely to solve the problem on its own e.g. it could be designed so the warmed air is admitted to the room down the face of this wall.

The surveyor specifically advised against applying external waterproofing - though it seems likely that if it needs re-applying every two years it is not (by definition) going to result in permanent damage.

With regard to the damp in the internal cross wall, the floor on one side is one step (~200mm) higher than the other; both are of insulated concrete construction with embedded underfloor heating pipes.

Depending whether you believe in the phenomenon, it might be that the new impervious floors have forced the damp up the wall, but it is notable that the other external walls to the ground floor are not damp. There is also no damp in the affected wall above waist height so I think it unlikely that it is falling damp. The paving outside the house is one step below the lower floor level and there is no realistic prospect of lowering the external ground level or installing French drains as the building has (at most) extremely shallow foundations.

 

[Gareth Hughes]

The surveyor specifically advised against applying external waterproofing - though it seems likely that if it needs re-applying every two years it is not (by definition) going to result in permanent damage.

well, yes, but ... isn't that a wee bit like saying that cement pointing doesn't cause permanent damage:


because after a few years you can always redo the whole wall:View attachment 1

Magic goo does cause permanent damge to the underlying material by trapping moisture (regardless of what Chuckey thinks).

 

[Nemesis]

Did the surveyor who recommended the dry lining offer any advice as to what to use?

Is there any possibility that condensation could be a cause of some of the damp?

Re the gable - have you looked very closely in case some of the pointing has a hairline crack or cracks?? It may be that the hard pointing coupled with a moving building has meant cracks have occured which are allowing in rain which is then unable to evaporate out again, and the water is meandering inwards. It doesn't take much of a crack, in driving rain, to allow moisture to penetrate. We have one or two of these in the fireplace recess, where the exterior has been badly pointed with cement in the past (soon to be removed along with some of the stone, sadly...) and in wet weather rain can trickle in to a surprisng degree - there is no plaster, so it dries out readily, but if there was it would I think make it pretty damp.

Is the damp widespread? Or localised?

The raised floor level could well be part of the other problem, but so much is guesswork.

Re French drains - as a general statement and not possibly applicable in your case - these can be constructed a small distance away from the building, not always right against the wall, in order to reduce moisture levels around a building.

Here's a bit of SPAB info re breathing buildings and locking in moisture:

http://www.spabfim.org.uk/pages/traditional_materials.html

I have no doubt that others will be able to add more in due course.

Nice pics Gareth!

 

[sharpener]

Did the surveyor who recommended the dry lining offer any advice as to what to use?

Is there any possibility that condensation could be a cause of some of the damp?

It doesn't take much of a crack, in driving rain, to allow moisture to penetrate.

Is the damp widespread? Or localised?

It is difficult to examine the pointing per se as the surface of the wall is very irregular (not like the sandstone "bricks" in Bradford!), and it would not surprise me if the stone - being very layered in structure, more like slate - is quite permeable along the cleavage planes. OTOH this wall is very thick and not exposed to driving rain. Having re-read the surveyor's report it is clear he does not think the pointing is the root of the problem.

Ideally I would prefer to take the interior finish back to the stone and start again, but having discussed this idea with him it seems there is no practical way of doing this given the friable nature of the stone.

The damp has spread over the winter to most of the length of the wall (~5m). Condensation can I think be ruled out; the wall surfaces are never wet to the touch and when surveyed last September the damp was present after a hot spell with the windows open. But if it is a contributory factor the proposed MVHR system and dry lining should both help.

The report says "In the long term consideration may need to be given to providing proprietary lining material with a void betwen it and the existing finish, ventilated at high and low levels. Such membranes can have an egg box-type profile on the hidden side to maintain the void and a surface, which can receive a plastered finish."

As it is >4m high at its highest point I am not convinced that the 5mm gap provided by e.g. Triton cavity membrane would give an adequate air flow on its own, its intended application is after all for drainage not ventilation. I had thought more in terms of vertical tanalised studding, leaving a 25-50mm air gap, then a vapour barrier, then 50mm insulation between cross battens and finally plasterboard. This would provide for ventilation of the cavity (I would extract the damp air via the MVHR system) and also a warm wall to avoid condensation. You may know of proprietary insulated boards which could go direct onto the studding.

Apart from the bit about cement with lime for pointing (omit cement) this isn't a bad guide:

http://www.bradford.gov.uk/NR/rdonlyres/78842480-8614-4D04-8ABE-F21315D3713E/0/StoneElevations.pdf

I assume you mean use 6 parts sand to 2 of lime i.e. the usual 3:1 mix? I had not seen the compromise of half lime, half cement suggested before. Otherwise a useful and interesting article, thanks.

BTW as you may have guessed I shan't be trying silicone coatings. If you could get an impermeable film thickness of 1/8mm it would be comparable to the epoxy coatings used to stop osmosis in GRP boats, but (a) unlike them most of the liquid is inert carrier (b) epoxy is a much better polymer system and (c) even that only lasts a few years.[

 

[chuckey]

Gareth et al, the thickness of a water proofing agent is only importent if its not watertight (think about it). You must have seen the nano scale technology stuff with water droplets sitting on tubes of silicon that are in the nano metre range. The reason is (like gortex, breathable fabrics etc) on these scales the water breaks up into droplets, which are rather larger the then gaps in the material. Its like trying to get a football through the park railings. So to make a park ball proof is not to throw up walls which are thick but discontinous, but just extend the railings. This where a thin substance is better cos' it gets into fine holes rather then trying to cover over them like thick paint.
Frank

 

[Matt Green]

As it is >4m high at its highest point I am not convinced that the 5mm gap provided by e.g. Triton cavity membrane would give an adequate air flow on its own, its intended application is after all for drainage not ventilation.

Very true. I'm not convinced that there's a massive need for ventilation in this case though. The gable wall isn't really causing an issue per se, just decoration irritation. It would be interesting to see if it's actually wet, or just surface phenomena. I'd strip it back, paint it with something breathable and let the MVHR gadget have a go first.

The cross wall sounds lik penetrating damp from the variation in floor heights. Some form of lining is pretty much the best option there short of altering the floor heights.

Matt