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Damp proofing sandstone structure

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Damp proofing sandstone structure

Postby Windows » 06 Feb 2022, 08:07

Where would I look for advice on damp proofing a sandstone building? One corner has a small amount of damp reaching the inside. The corner is next to the down pipe from the gutter, but don’t believe there is a leak. (Definitely no leak above ground - pipe goes underground - no obvious signs of unexpected water in ground). There is paving one side of the corner. Suspect the paving might be channeling small amounts of water next to wall during active rain. There is a flower bed on other side of corner. Dirt is against wall. There is no obvious barrier preventing moisture from dirt passing through wall, but don’t quite understand how old buildings constructed since building has to touch ground at some point. Presumably I need to compare outside ground level to inside level of *something*? Or will there be visible change in construction from outside? Removing couple of inches of dirt from against wall shows no visible difference to my untrained eye. All advice welcome.
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Re: Damp proofing sandstone structure

Postby Mike G » 06 Feb 2022, 09:08

Don't.

Stone buildings, along with other older-type constructions, work in a different way from modern buildings. You will be chasing your tail if you try to convert one system into the other, even if there was a successful way of achieving it. The way to deal with damp is to work out where it is coming from and deal with that issue. The rule is to get the ground level a minimum of 6 inches below your floor level everywhere. This can be difficult, as ground levels rise over the years, but it is critical. You might be digging up garden plants, or even building little retaining walls at some distance from the house walls. Try not to have hard landscaping hard up against the building, as rain will splatter a lot further up the wall than you think. Ideally, you want shingle or similar loose material against the house.

You will also need to check for sources of damp, such as a leaking gutter, or any nearby pipes or drains. Examine these carefully. You might post photos here if you like, and I'll comment if I can. I'm an architect specialising in ancient buildings, so although damp isn't my profession, it's something I come across all the time.

If you go to a spcialist damp company, beware that most are charlatans, and almost none of them understand old buildings. They'll want to drill holes and pump in chemicals, which has little chance of success in my experience. Worse still, they'll want to strip off your plaster to a metre high all round inside, and gunk up the walls with various water-tight products before re-plastering with some fancy plaster completely unsuited to an older property which actually relies on a soft plaster to work. These sorts of approaches are vandalism, and only hide the real problem (and then only for a few years).
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Re: Damp proofing sandstone structure

Postby Windows » 06 Feb 2022, 10:48

Thanks, Mike. That’s the kind of info I’m looking for! I’ll have to double check whether the floors are a full 6 inches above ground level everywhere. Btw there is an air brick that’s very close to the soil (within an inch), with another air brick maybe 8 inches higher almost directly above it, which struck me as unusual. The paved side is higher than the soil side by several inches.

In terms of determining quickly whether the problem is getting better, would you recommend a moisture meter? If so, do you have a recommendation? I can see that there has been a problem in this corner from marks, mould, paper lifting, and feeling colder on this part of the wall, but there’s not so much moisture that it feels wet.
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Re: Damp proofing sandstone structure

Postby droogs » 06 Feb 2022, 11:28

Sorry this is a little bit of a hijack. But is to do with sandstone. Does anyone know the stuff that can be sprayed on the outside of a sandstone walls after they have been sandblasted to keep air pollution from sticking and making them go black again.
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Re: Damp proofing sandstone structure

Postby Blackswanwood » 06 Feb 2022, 11:33

The Society for the Protection of Ancient Buildings are a good source of free advice on looking after traditionally built buildings. Having had help from them before I can confirm their advice and Mike’s comments above were perfectly aligned.
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Re: Damp proofing sandstone structure

Postby Mike G » 06 Feb 2022, 11:40

A moisture meter is a handy thing to have for the workshop, but they can be a bit misleading in houses. For a start, this is a long-term thing, and spot checks, unless you are keeping some sort of graph updated, can cause unnecessary alarm. BTW, wallpaper may not be helping your problem. Ideally you would have a stone wall plastered with lime, and then limewashed, allowing any moisture in the wall to evaporate slowly over time. Is this damp patch behind furniture? If so, relocate your furniture because airflow is ultimately what will sort this problem out.

If you resolve the ground level issues, and if you fix any leaks etc, then you won't actually have dry walls until after the coming summer. So long as you are aware of the sort of timescales we're talking about, then by all means stick a moisture meter on it.

I'm a bit puzzled by the airbricks. Could you post a photo or two? Stone buildings universally have solid ground floors in my experience, so an airbrick is pretty pointless unless they are servicing a fire or a boiler (or maybe a larder).

You sound as though you have paving hard up against the house. When you come to assess your floor level/ ground level relationship, have a look at that paving and see if it could be moved away from the walls. If you can get it a foot away and can fill the gap with shingle/ gravel then that will help a lot. The further the better.

As you're walking around the outside, constantly ask yourself "if I tipped up a bucket of water here, where would it go". You do get the odd drop of rain in Cumbria (I don't know if you'd noticed :) ), and it really musn't ever be allowed to pool against the house.
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Re: Damp proofing sandstone structure

Postby Mike G » 06 Feb 2022, 11:42

droogs wrote:Sorry this is a little bit of a hijack. But is to do with sandstone. Does anyone know the stuff that can be sprayed on the outside of a sandstone walls after they have been sandblasted to keep air pollution from sticking and making them go black again.


Yep, SPAB are your best bet for advice on this, but I am 100% certain they would advise against any form of surface treatment for stone. They may also have a view on sandblasting.
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Re: Damp proofing sandstone structure

Postby Windows » 06 Feb 2022, 12:57

I probably should have waited until I was back home before posting my question. Makes photos and accurate details a bit tricky. Sorry about that!

The building is 1910s. The floor/subfloor in the room in question is wood and there's a a 2 foot (?) void beneath the floor (at least in one area near where part of the wood floor can be pulled up). I think the joists are supported on brick (?) fairly close to the access point, so obscuring view of what's under rest of floor. There are cast iron air bricks all around the property. Mainly ~6 inches (?) above external ground level. (There are a couple much higher that are connected to bathroom fans.)

Although the house is built of sandstone with stone mullions, it has a similar feel to my parents' brick edwardian house which is also peppered with air bricks at a similar level.

The problem corner is situated in a built-in cupboard. I removed the wallpaper that had started peeling within the cupboard, but the rest of the walls in that room still have paper. We didn't put up the paper, so not sure of it's composition, but it's "soft" so would expect moisture to still evaporate into the room (although perhaps at a slowed rate?). Would that still be an issue? Perhaps other parts of the wall are getting damp, but also evaporating better because not in the cupboard?

Also not sure of the composition of the plaster.

Yes, there is paving hard up to the house on one side of the problem corner. If I tipped a bucket of water there, I would expect the water to run up against the house (moving west) then away again (moving north) toward a drain - assuming that there were no holes in the structure of the house or gaps between the paving and the house, which may be the assumptions that don't hold. The paving is in front of a door as well as connecting to paving that wraps two sides of the house, so it would be tough to remove. The difference in this area is that there is a very slight slope towards the house in one direction.
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Re: Damp proofing sandstone structure

Postby Windows » 15 Feb 2022, 12:59

Took a quick walk around now I’m home. The ground level (mostly paving) is not at a consistent level in relation to the house at all. House has what I’m going to call a skirting and there are air bricks in the course directly above where the skirting starts and also in the course directly below. I wonder if the upper ones are intended to replace the lower ones where the ground level has been raised?

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Air brick below soil level in bed
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Damp corner with drain pipe on left, soil vent on right, air bricks far right
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The photos above relate to the problem corner.
The photos below show additional air bricks and their relation to ground level.

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Another double air brick with lower one partly below ground level
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Lower air brick, no upper one
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There’s some evidence of plastic sheeting in the flower bed, but there’s soil between it and the wall, so its purpose isn’t clear.
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Re: Damp proofing sandstone structure

Postby Mike G » 15 Feb 2022, 13:14

Well, there's lots going on there. Downpipes, hard paving, and an outside tap. All potential issues.

Can you relate your floor level to the point where the masonry steps in with a "chamfer", (in woodworking terms). And can you get some photos from further out showing the whole wall.
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Re: Damp proofing sandstone structure

Postby Sheffield Tony » 15 Feb 2022, 13:20

That second picture seems to show paving with a patch of algae and a clean area in the middle, just like water is falling from above onto that spot ? Blocked gutter ?
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Re: Damp proofing sandstone structure

Postby Phil Pascoe » 15 Feb 2022, 14:03

One of three bits of dampness in my old Victorian house I found was caused by water tracking through two rotten wooden plugs on a downpipe clamp. I didn't find it until I renewed ceilings (and saw where it was tracking from) and just happened to be moving the downpipe around the corner from where it originally was.
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Re: Damp proofing sandstone structure

Postby Mike G » 15 Feb 2022, 14:30

Sheffield Tony wrote:That second picture seems to show paving with a patch of algae and a clean area in the middle, just like water is falling from above onto that spot ? Blocked gutter ?


Or the downpipe has a leak. They can be hard to trace, but on a fine, dry day put some newspaper or similar down in the area and then pour a bucket or two of water into the gutter. Watch what happens.
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Re: Damp proofing sandstone structure

Postby novocaine » 15 Feb 2022, 14:34

is that a slate damp course on the plinth (second brick down)?
it looks like it may move to above the return (because why not use another name for the chamfer) on the other side of the house.
either way it looks to be bridged and possibly to low given the raised ground work (which is obviously 12" above original level in some places given the blocking of the air grates).

from expereriance the return normally lines up with the internal floors as it's the a keying feature set when running the foundation, but I'm sure there are exceptions that break this rule.

for what it's worth, I'd consider pushing a little endoscope in to the cavity (there may only be one in the lower course, but it looks like it's a cavity wall from the higher placed air vents) to see how much crap is in there, bridging the two leafs above the DPC.
I'd also think about getting rid of the air vent that's half blocked by the paving, or moving the paving so it isn't letting water run through the vent.

All of these things run along side what Mike above has said, primary issues appear to be downpipe/gutter leaking, outside tap and raised ground level. everything above is secondary and could be causing increased issues.
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Re: Damp proofing sandstone structure

Postby Windows » 15 Feb 2022, 15:21

Approximately, the top of the internal floors line up with the top of the chamfer (which suggests the upper air bricks are above the level of the floors).

I think the light patch with no algae is where I removed a planter when I took the picture.

I managed to take a picture beneath the floor showing the corner in question.

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Under the floor
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The bricks on the left are along the wall where the flower bed is and where the air bricks are.

The bricks that are more facing the camera are where the paving and the down pipe are.

I think the closer bricks in that plane are the base of the chimney.
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Re: Damp proofing sandstone structure

Postby TrimTheKing » 15 Feb 2022, 15:27

Looks like a lot of damp in that corner, the sole plate timbers look wet (though difficult to tell with the lighting) on both planes coming out from that corner.

Looks like you need to clear everything out from against that external corner to start with and you might find some holes/gaps between stones that need dealing with.
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Re: Damp proofing sandstone structure

Postby Windows » 15 Feb 2022, 15:31

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Paved side
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Picture showing wall from further back

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Bed side - air bricks centred in this wall
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Last edited by Windows on 15 Feb 2022, 15:39, edited 1 time in total.
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Re: Damp proofing sandstone structure

Postby TrimTheKing » 15 Feb 2022, 15:37

Looks to me like you can actually see how wet the wall is on that last pic. Not what you want to hear, but I definitely think the only way you're going to discover the cause is to clear at very least that paving slab at the corner away, and dig below that and in the soil bed, to get down low and see what you can see.
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Re: Damp proofing sandstone structure

Postby Mike G » 15 Feb 2022, 15:49

Yeah, I'd suspect that downpipe, the gutter above, or the hopper. It looks like water is bouncing up the wall off the paving. The newspaper test I described earlier will soon tell you where its coming from. Also, stand out there in the rain and watch what happens. Binoculars can help.

Mark's right. Solve the leak first, then drying out starts with clearing everything back in that corner, including removing the path to the door. Re-route it temporarily. Get everything in that area down 6 inches from the bottom edge of the chamfer (or to the bottom of the air vent, whichever is lower), but you might find yourself digging even further in that corner if you find issues around the drain or the downpipe. Remove any plastic in the ground, and try to work out why it's there. It may be that this is an attempted bodge solution to the same problem.

I'd want a good look at that plate bearing the floor joists. If boards come up in that corner, then get one or two up and have a good look, otherwise you're going to need a leprechaun to go down and do the work for you. Unfortunately using children got a bad name with Victorian chimney sweeps. If that needs replacing your floor will have to come up. If it's OK, then I would put a fan in there for 6 months to move air around and dry things out. It's clearly damp in that corner, and it shouldn't be.

The air brick might also be an attempted fix for a long standing problem. It might also just be a red herring. With a chimney in that corner it may be there to provide an air supply for the fire.
Last edited by Mike G on 15 Feb 2022, 18:12, edited 1 time in total.
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Re: Damp proofing sandstone structure

Postby Windows » 15 Feb 2022, 16:59

Thanks everyone. Lots of useful advice. I will assume nothing and will check the gutter, hopper, down pipe at the next rain (which I’m sure will be soon). Looks like I’ll be lifting the paving and doing some digging too. Don’t have an easy way of getting closer to that corner from inside the room without cutting I think, but might try to see what’s under the bottom of the built in cupboard first. (Also considering whether I can get a mini drone to fly under the floor and get a better look. Endoscope is also on my list - could have used one last month).

Once the water is no longer getting in, I’m thinking it might dry pretty fast. It’s like a howling gale blowing through that underfloor space. If I do have to lift the floorboards I guess I could use the opportunity to add insulation and relag those pipes.
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Re: Damp proofing sandstone structure

Postby TrimTheKing » 15 Feb 2022, 18:14

Plenty of space to slide around under that floor, as long as you're not claustrophobic... :? :lol:

I used to slide around under our old place that was around that depth, to pull cables for my surround sound rear speakers. Hardest part was getting through the gaps in the underground walls, which in a couple of places were only two bricks wide.

This meant I couldn't get my shoulders through without going one arm first, pushing against the floor with my feet with the other arm trapped by my side, then once that arm was through I had to use both arms to push against the bricks to pull my fat ass through!

Wife got claustrophobic just watching me down there and had to leave the room! :lol:
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Re: Damp proofing sandstone structure

Postby Windows » 15 Feb 2022, 18:22

I couldn’t easily get the phone closer to the corner, but I could get some extra light down there, so I took another couple of pictures. Looks a lot better with more light.

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Light shining in corner
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Light shining on side wall
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Re: Damp proofing sandstone structure

Postby Windows » 15 Feb 2022, 18:47

I don’t think I’d get claustrophobic in that space, Mark, but my current access hole is about 12”x5”. You sound like a more daring person than me. You wouldn’t get me going anywhere that I couldn’t turn around pretty easily.
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Re: Damp proofing sandstone structure

Postby Mike G » 15 Feb 2022, 20:25

It's not the depth, it's the relationship between the hole size and the depth. If you can drop straight in or climb straight out, then a small entrance is OK. If you have to turn an immediate right angle, as here, then.....find a leprechaun. If you can't roll over in the gap under the floor (or in a roof), then you probably shouldn't be in there. That means the width of your hips is roughly the minimum height you can crawl around in.
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