Another tedious damp problem!

[jaykayem]

Hello all, I've been lurking on the site trying to resolve a damp issue in our mid C19 Derbyshire barn conversion,and I think I've devised a plan of action, but hoped to have it 'signed off' by the good folk on the PP forum!
The problem: Penetrating damp across a kitchen wall (the exterior of which is exposed to wind and rain);
Poor state of mortar - holes, cracks, salt (mixture of lime and cement, applied ad hoc over the years by previous occupants);
A number of cracked, rawlplugged & spalled bricks (brickwork and mortar discoloured by damp in patches);
Brickwork has been sandblasted, which may or may not have removed an element of protection;
Downpipe doesn't lead anywhere, just spills out onto driveway by corner of exterior kitchen wall, the foot of which is a mess of mossy brick.

I have removed the interior plaster; a couple of bits of bubble membrane sat behind some patches of plaster, but not all the way across the wall. Patches of this interior brickwork were pretty wet.

My plan is to pick up a dehumidifier and dry this all out as much as possible before tackling the repointing using lime mortar (although the threads on slaked lime, lmie putty etc completely baffle me!).

The bit where I get really stuck is the 'seal or not to seal' debate. Apparently farm buildings of this age were not meant to keep out water. Some people recommend painting the exterior brickwork with silicone sealant, others are appalled at the idea. Should I therefore 'seal' from the inside using water-repellant plaster and another plastic membrane, plaster over the top and hope for the best?

Apologies for the length and repetitious nature of the post, I just can't seem to get any consensus on what to do for the best!

Thanks in advance.

 

[chuckey]

If you seal the inside of the wall, the water the bricks absorb will percolate down the inside of the wall and appear below the water proofing, putting floor joists at risk? or at least needing some form of sump/soakaway around the subfloor to get rid off it.
You don't say if the wall is single skin (4 1/2" thick), double skin (9" thick) or cavity (11" thick). All old brick walls have the odd hole or cracked brick but this does not usually cause any trouble.
Some times you just get a "bad" brick, leading to an odd spot of damp, this can be normally be cured by an exterior application of some silicone type sealer.
If it is built of a none waterproof brick without a cavity, the best thing to do is to render the inside with a waterproof render taking the render right down to below the floor level and put in extra airbricks to try and keep the floor joists dry.
Frank

 

[worms]

our mid C19 Derbyshire barn conversion...

When was it converted? (I know this may seem an obtuse question, but it may give those with more expertise than me some clues as to how the whole building is functioning - my own property is also a mid 1800s farm building but a lot of the issues relate to late 1940s techniques used in the conversion).

putting floor joists at risk? ...extra airbricks to try and keep the floor joists dry.

I didn't see any reference to whether or not the floor is suspended, or whether the solum is earth or a concrete sub-floor, so again, a bit more info might help the experts (of which I am not one).

Apparently farm buildings of this age were not meant to keep out water...

Perhaps, but I am sure they were not meant to remain saturated either. Most old farm buildings that I have known are inherently dry structures except where the rainwater goods or roof have failed. However, I am probably accustomed to rubble construction farm buildings rather than brick which might have functioned differently.

 

[Penners]

For what they're worth, here are my inexpert thoughts.

As Frank mentions, the construction of the wall is important, and could affect the way that you tackle problem. However, I'm going to assume that it's a solid brick wall - ie, no cavity.

In theory, if you were able to eliminate all damp from the brickwork, I suppose you could coat it inside and out with something waterproof, and preserve the dry wall in the long-term. But I reckon it's virtually impossible for you to do this - you have identified penetrating damp, plus various other structural defects that are adding to the damp problem, and there may also be other factors such as rising damp, that you haven't been able to spot. So, given the risk of trapping current or future damp in the wall, I definitely would not apply any waterproof coatings.

By the way, I do believe that the sandblasting may have exacerbated your problem by removing the outer "crust" of the brickwork.

So here's what I think I would do:-

1. Expose the brickwork on both sides - I infer that you have already done this - and (as you plan) try to dry it out as much as possible. Just don't be too vicious with a dehumidifier... suck out the moisture gently.

2. Replace any spalled bricks and repair any defects, and any associated problems with surface water drainage, plumbing, etc.

3. Replaster the interior in lime plaster, and repoint the exterior in ditto.

4. If, after some time, you feel that the problem still exists, then you may have to render the exterior in lime plaster, too, then limewash. As this would in effect waste the work that you've done in repointing, you could do this at stage 3 above instead of the repointing, if you prefer (I think I would).

The problem with damp is that, not only is it difficult to be certain what is causing it, but it's also difficult to know when/whether you have solved it. It takes a considerable time to be able to see the results of any measures you have taken. You therefore have to decide for yourself just how patient you are prepared to be at every stage of the campaign. If you have the time and the patience to do so, it could be prudent to carry out each of the above stages in isolation, then wait for several months to see what the outcome of that action has been. If it's successful, you stop. If not, you move on to the next stage.

But if you haven't the time to do this, then you may feel it's better to just press ahead with the whole project.

No promises or guarantees, but that's a suggested plan. Do let us know what you decide to do, and in the long term what success you achieve.

 

[Cloudscape]

The first thing I would do with any building is make sure that rainwater is managed. That means, if the roof is OK, the next job is where the run-off water goes. The first thing I did for this house was make sure that the rainwater that was sploshing at the base of walls was channeled as far away from the building as possible.

The dodgy downpipe might not be related to the problem you describe, but it needs sorting.

 

[jaykayem]

Thanks, i'll try to give a bit more info. The wall is a shade under 11" but I'm 99% certain there is no cavity. The conversion was done around 20 years ago by a local builder with a less than stellar reputation for quality and meticulousness. The floor is simply a tiled concrete job, which is fine. I want to replace these tiles in the near future, so I can tie that in with the damp work.
I don't want to seal any moisture in the bricks so perhaps another p plaster membrane, with silicone sealant on the problem exterior areas?
Penners, thanks for the plan, which is all feasible except the external lime, which I am certain would be verboten by our local conservation officer. As for sealing, you're right, there's no way I could be confident of having eliminated all ingress of water. I will do the above, and see how it goes over winter, and report back!
Cloudscape, I'm convinced the downpipe is a big part of the problem, expecially as it handles an enormous amount of rainwater from a very long roof. I've sealed leaking brackets (which, like your house, caused drips to bounce off the ground and up onto the wall) and so on, but will monitor the routes of rainwater as this wet period continues!
Thanks again

 

[jaykayem]

Chuckey, can I use waterproof render without having to lay a load of air bricks if I have a concrete floor? Will it seal water in and cause further problems down the line?

 

[Gervase]

Chuckey, can I use waterproof render without having to lay a load of air bricks if I have a concrete floor? Will it seal water in and cause further problems down the line?

Aye, sure as eggs is eggs. There are two schools of thought, however. If some nobber has already half ruined the building and you're just after a quick cosmetic job so you can sell the place on and turn a few bob, then follow Chuckey's advice.
If you actually want to live in the place and pass it on to your kids in good heart, then Chuckey's talking cobblers, I'm afraid. If you have any wooden elements in that wall - joists, lintels, door and window frames, you name it - they're not going to like being kept in a permanently damp environment thanks to some crap waterproof cure-all. Sort out the hat and boots, ground levels and drainage, and keep the fabric breathable. Bare stone might look pretty, but for maximum weatherproofing consider a lime rough-cast render or harling on the windward side. At the very least, give the whole place a few coats of limewash.
But don't waste your money on 'waterproofing'. For sure, the place might stay sound as a drum for 15 or 20 years, but thereafter...

 

[Schoolmarm]

Brilliant advice there from Gervase.

 

[Flyfisher]

We took on our "project" almost three years ago and it had many areas of damp, which all seemed due to failed roofing, guttering and downpipes. One particularly bad bit was due to a failed downpipe leaking onto a wall from a joint halfway up the wall. Over a number of years this had resulted in a saturated wall, blown plaster inside and the almost complete destruction of a wooden lintel above a window (exactly as per Gervase's point above). All the other downpipes were also dubious and most of the drains were blocked so even if the downpipes did work they simply deposited water right against the walls of the house.

Since my priority was to fix the roof I needed a quick, temporary fix for the downpipes. First, I bought a 50m length of 4-inch flexible cable ducting (the sort of thing they run cables through). Then I removed the lower parts of failed downpipes, up to the point they were good, and fixed them into the flexible ducting, cutting it to a suitable length to dump the rainwater into the grass about 3m from the house. Effectively, this was an 'above ground' soakaway, without all the digging. I then removed all the internal gypsum plaster from the worst-affected wall.

Within less than 6 months the wall felt bone-dry inside, and this was without any internal heating or dehumidifiers.

I'm certainly no expert and this is our first period property, so my experience is limited, but I've been amazed how good ventilation (and I include breathable materials in this respect) and proper rainwater management can transform a property. I've only just got around to digging proper drains this year but the flexible ducting has done a great job in keeping rainwater well clear of the house. In fact, the new 'proper' drains won't do a better job, they'll just look a bit better!

Based on all this, I would deal with your downpipe as a matter of priority and get all that rainwater well away from your walls.

 

[FamilyWiggs]

jaykayem,

Welcome to the forum.

Damp has been covered many many times on here, so fear not - you are not alone.`There are two schools of thought, and in my inexpert opinion the bulk of the advice falls into the Gervase/Penners/Flyfisher approach, rather than Chuckey.

I wouldn't want to waterproof anything - I made the mistake of sealing with black gunge a dripping subterranean wall. I thought I was so clever in also painting the gunge 18 inches across the concrete floor (not my addition) too. 12 months later I can see the damp leaving marks on my lovely Heather Brown floor, exactly 18 inches into the room.... grrrr. I now have to dig french drains around the external wall sometime to solve the problem.

Lesson learned is that you can not seal damp out - water will travel until it can escape. It may take a while,but ultimately it is pure physics and Cnut discovered the futility of ignoring that.

I would sort out the rainwater goods first and then proceed exactly as Penners describes - stepwise if possible.

 

[JoceAndChris]

And just to say - your problem isn't tedious, not to me, anyway. I love reading about how to get rid of damp, we all do, otherwise we woudn't keep reading and posting in these threads. 8)

 

[MdB]

Our internal wall had at least 3 different tanking / sealing attempts performed on it combined with multiple layers of cement plaster and paint. It had all failed leaving a very damp wall which did a good job of growing mould. Two years ago, all this cr@p was removed (between 100mm and 150mm worth) and the bare stone and mud wall is now completely dry having been allowed to breath and the damp evaporate. Wood that had been in the damp wall trapped behind a layer of something partially waterproof had crumbled to dust. See the "Stripping cement render, updated" for some pics of the outside.

 

[Cloudscape]

Is the internal surface of the wall improving now that the plaster has been removed? Is it drying out at all? I only ask because, if the plaster had been very damp over time, it might have been actively pulling in moisture (it had become hygroscopic). We had a few patches of this at the last house. It looked like penetrating damp, but wasn't.

 

[Matt Green]

The problem: Penetrating damp across a kitchen wall (the exterior of which is exposed to wind and rain);

Some times you just get a "bad" brick, leading to an odd spot of damp, this can be normally be cured by an exterior application of some silicone type sealer.

Through an 11" wall. Eleven inches of masonry. 'Legs' 11.

Sorry to labour that point, but having looked at damp in a whole lot of solid walled buildings if the best answer is driving rain through a wall that thick- isn't it time for a reality check?

You haven't told us how you know the wall is damp. What symptoms are you or were you seeing?

And if you decide to use a waterproofing option you need to think how you are going to tie it into teh floor. the weka point in such retro-fitting strategies is the wall/floor junction and either the bottom foot of plaster will blow pretty quick and fall off or the edge of the screed will distintergrate (hence Chuckey's plan on bringing it below a suspended floor- the water in the wall would evaporate into teh floor void. With a solid floor it gets more difficult).

And what are the ground levels like?

M.

 

[Penners]

Brilliant advice there from Gervase.

As always.

Jaykayem - be aware that Gervase knows what he's talking about. I mean really knows.

 

[jaykayem]

Thanks very much for the advice so far - it has inspired me to spend the whole rotten day bodging temporary fixes to get the rainwater away from the house, a la Flyfisher. I took up the paving bricks beneath the spewing downpipe: lo and behold a gaping whole where a chunk of a brick should have been. Since I can't try my hand at repointing in this foul weather, I just filled in the hole with sharp sand, replaced the bricks, and re-routed the rainwater flow with some angled joints and 5m of downpipe back down the drive and away from the house.

I have also been digging round the other side of the kitchen where we have a constantly overflowing drain - turns out it is just a soakaway straight into earth with a very high clay content. Should i dig this out and replace with sand for a better flow? I will also try to help the soakway out by using a rain butt.

Matt and Cloudscape, I think we have a combination of hygroscopic damp and penetrating damp as some of the plaster behind the units looked as though it had been wet for some time - I barely had to tap it for it to drop off. Does penetrating damp lead to hygroscopic damp? The amazing thing about all this is that a local, well-known damp company tackled the damp just before we moved in 12 months ago, as part of the mortgage approval. Much of the plaster has been wet all this time, and I was told by the company that it was just "drying out", and they weren't legally obliged to come back until after 8 months. Small spots of discolouration in the plaster developed, and just kept getting bigger. These corresponded to the dab points. I had them back in under the guarantee but the guy was as helpful as a door in a submarine. Having knocked off their plaster, I can see the membrane wasn't taken far enough across the wall, there were patches aplenty over the dabs, and there may well have been a breach of the dpm. So I could get them back in, but to be honest I don't want them anywhere near my house again; I believe they were the clots who did the original damp proofing20 years ago, which virtually proves Gervase's point about longevity.

Patches of the bare brick walls do seem to be drying out, and the smell is starting to abate after 10 days. There is still lots of moist brick, from the foot of the wall to the ceiling, so deciding whether it's rising, penetrating, or hygrsocopic damp is tough! Matt, How do I check ground levels?

Thanks again for the help, it's very motivational to know people have experienced and overcome the same problems.

 

[Cloudscape]

There's a formula somewhere on PPUK that helps you work out how long the wall will take to dry out, once water ingress has been stopped. Something to do with the thickness of the wall... times the number you first thought of, or something. :?

I had a two-brick-thick wall in Manchester that had been treated to an overflowing gutter for a few years. It took years to dry out.

Hygroscopic salts form after prolonged dampness. I'm sure it's possible to have more than one sort of damp at the same time. Removing the internal plaster was a good move.

 

[Flyfisher]

I think the rule of thumb is one inch of wall takes one month to dry out, but it's very approximate and will vary a lot depending on the wall construction. But it gives an idea of the sort of timescales involved, which is not unreasonable really - a wall that has been subject to regular soakings over many years can hardly be expected to dry out overnight when the gutter or downpipe is finally fixed.

I'd say that jaykayem's "rotten day" will turn out to be the best day's work in helping to solve the problem. Just a thought though; it might be worth not replacing the paving bricks for a few weeks to help the ground below dry out thoroughly.

I'm not sure about soakaways in clay soils but there is probably loads of info on the web about how to size them based on the roof area to be drained. I wouldn't rely on a water butt to help with drainage. I recently fitted a 205 litre barrel to a downpipe and it filled up in less than 5 minutes in one of the recent heavy downpours. Not 'typical' rain, I know, but it gives an idea of the volume of water involved and, of course, when the butt is full it's of no help with the rainwater anyway. A water butt is a good idea for many reasons but you still need a drainage system that will cope with all the water your roof will collect.

 

[Matt Green]

Matt and Cloudscape, I think we have a combination of hygroscopic damp and penetrating damp as some of the plaster behind the units looked as though it had been wet for some time - I barely had to tap it for it to drop off. Does penetrating damp lead to hygroscopic damp?
[snip]
Patches of the bare brick walls do seem to be drying out, and the smell is starting to abate after 10 days. There is still lots of moist brick, from the foot of the wall to the ceiling, so deciding whether it's rising, penetrating, or hygrsocopic damp is tough! Matt, How do I check ground levels?

Thanks again for the help, it's very motivational to know people have experienced and overcome the same problems.

Hygroscopic salts mean ground water ingress. Water moves through soil and takes disolved salts with it, leaving them at the surface when the water evaporates from the wall into the room when the rooms Relative Humidity is high. When the room's RH drops the salts in the surface layers of the wall absorb water from the room back into it. This to and fro breaks down the surface and spoils your decorations.

Ground levels: Measure to the base of a window pane inside*. Measure the same distance outside. The difference is the difference in internal floor height and external ground level. Your floor needs to be 6" above external ground so that water moving into the base of the wall and rising will evaporate to the outside before it gets to the height of your plaster to start spoiling it (or joists to decay if timber). Seal the outside and this wont happen: the water will keep going up and come out through your plaster. Use water-proof plaster and theory is that the water will stay in the wall. What happens in practice is that the plaster falls off in sheets; the wall/floor junction gives out; or you come to sell the house and a guy in a suit will tell you there's a damp problem. :|

Depends entirely upon what you are going to do with the house.


Matt.
*if you haven't got a window on that wall you'll have to take a reading from one nearby and get creative with chalk and tape measures to work it out.