Help! Cannot resolve damp issue (5 roofers later)… mushrooms growing from wall

[jhbc93]

Hello

I am at the end of my tether trying to find the source of damp on my gable end walls. The original house (1750s) is sandstone with external render (lime, I believe) and has two wings which appear to be brick (also with render). I believe the wings were added in the 1800s. The original house is ok but one of the wings is particularly bad.

All the internal walls are cavity walls (no cavity wall insulation) so the only damp which is obvious is above the windows where there is a lintel and the windows are “boxed”:



The internal brick in the loft space is so damp that mushrooms are growing out of the brickwork:




Here is a picture of the exterior:


There is no lead flashing, just cement skews. We had these re-cemented a year or so ago but this hasn’t seemed to help. There is no obvious damp on the sarking boards.

The render is not in great condition and there are some hairline cracks in this. I don’t know if this would be enough to allow water to penetrate the brickwork internally?

The chimneys are not capped and there are no fireplaces in use on that side of the house. Could uncapped chimneys cause water to penetrate so widely across the wall?

The pointing of the brickwork internally is very old and some bits are falling out. Would repointing this and waterproofing internally just push the problems elsewhere?

Any advice would be greatly appreciated.

Many thanks

JHBC

 

[malcolm]

The mushrooms in the loft should be easy. The mortar looks original so you'd guess it is lime. There ought to be ventilation in a loft which is normally in the form of a gap in the eaves. There's a special thing in Scotland where you have the underside of the roof lined with wood. My sister's house in Glasgow is like that and she has a good wind in the loft. If the roof tiles have previously been lifted to fit a waterproof membrane they should have added vents in the eaves. A breathable membrane is not enough and you still need eaves ventilation.

If the render were lime and painted with a breathable paint it wouldn't have grey stains on the exterior paint. Your render looks recent, maybe 80s. That's not ideal but if you have a cavity it's not the end of the world. It's going to be bridging across the cavity that is causing damp over the lintel. It's worth figuring out construction of the lintels. With a window hole going through there is access to drill a hole or two that can easily be filled and stick a cheap inspection camera through.

 

[Matt Green]

The mushrooms are Peziza species- they grow on ringing wet wood, so there is likely some within the wall. Not a huge decay risk- it's more likely the timber will compress and cause cracking.

 

[Stevers]

That row of headers suggests solid wall not cavity, though there could still be a cavity lower down. The masonry upstands on the gable ends are a potential weakness from water penetration on top and where it's flashed (or no longer flashed) into the slates. Cracks in masonry painted render on exposed elevations on solid walls not a good thing as water always seems to find it easier to enter than exit. Open chimneys pots were a problem for us when the lid on one of our clay cowls blew off, and rain penetrated all the way down to the ground floor and even basement.

It is perfectly possible that typical modern home 'upgrades' have removed your home's ability to regulate damp. The roof space could have been effectively sealed up, masonry paint on harling could stop it from drying out, fireplaces closed so flues no longer vented, total draught proofing (double glazing etc.) in conjunction with modern living conditions creating condensation - the list of things that you might not (or might) get away with on a house like that (and ours actually) in an area of high rainfall is quite a long one.

 

[jhbc93]

The mushrooms in the loft should be easy. The mortar looks original so you'd guess it is lime. There ought to be ventilation in a loft which is normally in the form of a gap in the eaves. There's a special thing in Scotland where you have the underside of the roof lined with wood. My sister's house in Glasgow is like that and she has a good wind in the loft. If the roof tiles have previously been lifted to fit a waterproof membrane they should have added vents in the eaves. A breathable membrane is not enough and you still need eaves ventilation.

If the render were lime and painted with a breathable paint it wouldn't have grey stains on the exterior paint. Your render looks recent, maybe 80s. That's not ideal but if you have a cavity it's not the end of the world. It's going to be bridging across the cavity that is causing damp over the lintel. It's worth figuring out construction of the lintels. With a window hole going through there is access to drill a hole or two that can easily be filled and stick a cheap inspection camera through.

Hi Malcolm

Thanks for getting back to me and for your helpful response.

The house was renovated in the 1980s but I don’t know if that section of the roof was replaced. It has the old/original tiles and a felt membrane. We haven’t replaced that section but there aren’t any obvious vents that I can see. We were thinking about putting vents in the gable end which we did at the ground level. The cavity is small but I am assuming it is going to be the same construction:


If the lime render has been painted with an inappropriate coating, is there anything that can be done to remove that without removing the render? We got paperwork for the coating when we bought the property which said it was done in 2015. I have since purchased some lime render suitable paint which I intended to use for touching up but I’m not sure if there’s much point in putting this on top of an unsuitable coating.

It sounds like the open chimneys could definitely be at least one source of the damp.

Edited to add: the lintels above the window are concrete.

 

[jhbc93]

The mushrooms are Peziza species- they grow on ringing wet wood, so there is likely some within the wall. Not a huge decay risk- it's more likely the timber will compress and cause cracking.

Hi Matt

It doesn’t look like there is any timber in that area - do these only grow on wood?

Thanks

 

[jhbc93]

That row of headers suggests solid wall not cavity, though there could still be a cavity lower down. The masonry upstands on the gable ends are a potential weakness from water penetration on top and where it's flashed (or no longer flashed) into the slates. Cracks in masonry painted render on exposed elevations on solid walls not a good thing as water always seems to find it easier to enter than exit. Open chimneys pots were a problem for us when the lid on one of our clay cowls blew off, and rain penetrated all the way down to the ground floor and even basement.

It is perfectly possible that typical modern home 'upgrades' have removed your home's ability to regulate damp. The roof space could have been effectively sealed up, masonry paint on harling could stop it from drying out, fireplaces closed so flues no longer vented, total draught proofing (double glazing etc.) in conjunction with modern living conditions creating condensation - the list of things that you might not (or might) get away with on a house like that (and ours actually) in an area of high rainfall is quite a long one.

Hi Steve

Thanks for your response. To the best of my knowledge it is a cavity wall but the cavity may be very small. Pic of cavity in other part of the house believed to be constructed at the same time:


Here are some better pictures of the cracked render. These seem minor but it’s hard to say for sure because there is no easy way to access that wall due to a conservatory being below.



It seems like the chimneys are most likely a problem. I’m not sure whether water ingress from the chimneys could also cause the cracking to the render?

 

[Lacan07]

Hi Steve

Thanks for your response. To the best of my knowledge it is a cavity wall but the cavity may be very small. Pic of cavity in other part of the house believed to be constructed at the same time:
View attachment 12900

Here are some better pictures of the cracked render. These seem minor but it’s hard to say for sure because there is no easy way to access that wall due to a conservatory being below.

View attachment 12901View attachment 12902

It seems like the chimneys are most likely a problem. I’m not sure whether water ingress from the chimneys could also cause the cracking to the render?

That won't be a cavity wall in the modern sense, my house was built approx 1800 and there's a small gap at the centre of the solid brick wall construction.

Are you sure that external render is lime? Looks like the standard sand and cement to me, when it cracks and water gets in behind you're in trouble. Once its in it won't be able to escape very easily.

 

[Stevers]

That's not a cavity, just the normal gap between the stretcher bricks on a solid wall that haven't (for whatever reason) been filled with mortar.

Your starter for ten is that the inside of the gable end should not be wringing wet. The crumpled paper suggests a previous occupier with an obsession with draughts. Your roof has sarking boards as would be expected up there - any sign of condensation on them? You could start by making sure that any eaves venting is not blocked, and that as little moisture as possible is getting into the loft from showers and cooking.

The chimneys pots would benefit from cowls, but access will be a problem. Are the flues vented at the fireplace end?

The stonework on top of the gable end is not ideal for keeping water out, particulary the junction at the chimney and the kicker at the bottom where it's flat. If that's stonework has deteriorated it could let water in particularly if there are any cement repairs to it.

 

[jhbc93]

That won't be a cavity wall in the modern sense, my house was built approx 1800 and there's a small gap at the centre of the solid brick wall construction.

Are you sure that external render is lime? Looks like the standard sand and cement to me, when it cracks and water gets in behind you're in trouble. Once its in it won't be able to escape very easily.

Thank - I didn’t know that and assume that any cavity made it a cavity wall! The internal walls are all cavity walls (I.e they are boxed out from the actual brickwork).

I’m not 100% sure that it’s lime render and I’m not sure how to be sure. We chipped one small loose bit off an put it in vinegar and it fizzed which was what made me think it was lime but I could be wrong.

 

[jhbc93]

That's not a cavity, just the normal gap between the stretcher bricks on a solid wall that haven't (for whatever reason) been filled with mortar.

Your starter for ten is that the inside of the gable end should not be wringing wet. The crumpled paper suggests a previous occupier with an obsession with draughts. Your roof has sarking boards as would be expected up there - any sign of condensation on them? You could start by making sure that any eaves venting is not blocked, and that as little moisture as possible is getting into the loft from showers and cooking.

The chimneys pots would benefit from cowls, but access will be a problem. Are the flues vented at the fireplace end?

The stonework on top of the gable end is not ideal for keeping water out, particulary the junction at the chimney and the kicker at the bottom where it's flat. If that's stonework has deteriorated it could let water in particularly if there are any cement repairs to it.

Thanks Steve, I didn’t realise that wasn’t a cavity wall. The crumpled paper was put in by me (recently) to try and stop the water seeping down and causing more internal damage. The brickwork doesn’t appear to be visibly dripping even in heavy rain but it is damp to the touch and the paper does get wet.

No signs of condensation on the sarking boards that I have been able to see, but I don’t know if we have eaves vents. If these should be visible from within the loft I’m going to say that we don’t have them. When we moved in there was insulation in the rafter which we removed and put between the joists instead. I’m not sure if eaves vents are something which would have been installed in the 80s (if the roof was redone then - it may not have been).

For capping the chimneys, I think we could do this with a cherry picker. I’m not sure if the flues are vented at the fireplace end or how to check this? I’ve no clue where the fireplaces would be. Directly below that gable end is my bedroom and bathroom, then the floor below is the kitchen. We stripped that part of the bedroom and bathroom back and I don’t recall seeing any evidence of fireplaces there but admittedly I wasn’t looking.

The stonework has been repointed in places but this was done with cement. A waterproofer was also applied to it but the roofers were cowboys so I’m not sure how carefully this was done.

 

[aockenden]

Thank - I didn’t know that and assume that any cavity made it a cavity wall! The internal walls are all cavity walls (I.e they are boxed out from the actual brickwork).

I’m not 100% sure that it’s lime render and I’m not sure how to be sure. We chipped one small loose bit off an put it in vinegar and it fizzed which was what made me think it was lime but I could be wrong.

The whole vinegar test thing bugs me. Even today, plenty of builders will cut their Portland with non-hydraulic hydrated lime powder. Also isn't Portland itself still alkaline? I think that test is imperfect at best, possibly mostly useless. I think interior color and hardness are your best indicators. If it's super hard and a dull grey color inside, then it's probably got a high cement content.

I agree with Lacan. My eye tells me that's very likely some kind-of roughcast cement render (the cracking, the texture, the staining, etc.). Assuming it IS cement, then this could very well be contributing to the buildup of moisture in that wall. Here's what our thickly cement-rendered Gable wall (also under a leaky chimney and also with cracks in the render) looked like on the day we removed the render, and a month later after it had dried out considerably. A similar situation could be playing out on your wall.

 

[Matt Green]

Hi Matt

It doesn’t look like there is any timber in that area - do these only grow on wood?

Thanks

Yes, fungi grow on decaying matter. They need a source of carbon to create the structure used in the sexually reproductive part of their lifecycle (the 'mushroom' or 'fruiting body').

 

[jhbc93]

The whole vinegar test thing bugs me. Even today, plenty of builders will cut their Portland with non-hydraulic hydrated lime powder. Also isn't Portland itself still alkaline? I think that test is imperfect at best, possibly mostly useless. I think interior color and hardness are your best indicators. If it's super hard and a dull grey color inside, then it's probably got a high cement content.

I agree with Lacan. My eye tells me that's very likely some kind-of roughcast cement render (the cracking, the texture, the staining, etc.). Assuming it IS cement, then this could very well be contributing to the buildup of moisture in that wall. Here's what our thickly cement-rendered Gable wall (also under a leaky chimney and also with cracks in the render) looked like on the day we removed the render, and a month later after it had dried out considerably. A similar situation could be playing out on your wall.

View attachment 12905

View attachment 12906

Thanks Aockenden. This is what it looks like:


Does this look like cement rather than lime? What did you do after you stripped the cement from yours - just re-point? Is there any other solution than to take it off? Removing it is not really feasible for us due to the size of the house…

 

[aockenden]

Thanks Aockenden. This is what it looks like:
View attachment 12907

Does this look like cement rather than lime? What did you do after you stripped the cement from yours - just re-point? Is there any other solution than to take it off? Removing it is not really feasible for us due to the size of the house…

It's a very small pic but looks like a dull grey to me (which has a very thin coating of white paint on one side). Assuming the sample is dry, then the color tells me it's probably Portland cement. How hard is it? How hard do you have to smash it with a hammer to get it to crumble?

On the wall I showed above (which was South West facing, aka very exposed to driving rain in West Wales) we re-rendered it in lime. All 3 of the other walls on the house we just repointed in lime (after removing cement render and sandblasting of course).

I can't in good conscience recommend anything other than total removal of cement render from old stone houses. Sry, I know that's a bitter pill to swallow, but we've learned to embrace the drudgery and just get it over with. It sucks, but you've only got to do it once. An SDS is absolutely worth the investment if you decide to remove it. I removed all the external cement from all 4 walls of our stone cottage with hammer and chisel and it sucked. That being said, limiting ingress of water by filling cracks, fixing the possibly leaky chimney, and trying to restore breathability on the inside surfaces of the wall is probably your best bet if you can't remove the cement externally.

 

[jhbc93]

It's a very small pic but looks like a dull grey to me (which has a very thin coating of white paint on one side). Probably Portland cement. How hard is it? How hard do you have to smash it with a hammer to get it to crumble?

On the wall I showed above (which was South West facing, aka very exposed to driving rain in West Wales) we re-rendered it in lime. All 3 of the other walls on the house we just repointed in lime (after removing cement render and sandblasting of course).

I can't in good conscience recommend anything other than total removal of cement render from old stone houses. Sry, I know that's a bitter pill to swallow, but we've learned to embrace the drudgery and just get it over with. It sucks, but you've only got to do it once. An SDS is absolutely worth the investment if you decide to remove it. I removed all the external cement from all 4 walls of our stone cottage with hammer and chisel and it sucked. That being said, limiting ingress of water by filling cracks, fixing the possibly leaky chimney, and trying to restore breathability on the inside surfaces of the wall is probably your best bet if you can't remove the cement externally.

Damn, I thought I had at least one thing right with it being lime! Unfortunately that’s an old pic so don’t have the piece anymore to check how hard it was.

I commend you for your efforts on removing all that render! Unfortunately it’s just not feasible for us I don’t think due to the size of the house. I’d probably be at it for 5 years and definitely can’t afford to pay someone to do it! I think we’ll start with the chimney and getting some vents in the loft to ensure airflow and hopefully that’ll make a difference. Thank you so much for the helpful advice.

 

[Stevers]

If you're not seeing condensation on the sarking, then it's less likely that the damp gable end is due to condensation, though if the gable end is already suffering with penetrating damp, condensation may still be a factor as it will be cold from being damp.

We looked at getting a cherry picker to replace my missing clay cowl lid (it had cleared the porch and paving below, landing in soft earth). Because we're on a B road, we would have needed traffic lights and some sort of license, making it even more expensive than scaffolding. Of course scaffolding gave me more time and allowed me to paint the bargeboards. Once I was up there I realised that the crumbly recycled verge slates would benefit from being replaced and the flashing needed sorting anyway, so I was able to do that too.

Not keen on the stonework detailing above the leaky window, lots of scope there for problems with all the ledges and cracks. Not a lot of material above the window to keep it dry either. The interior looks to be modern gypsum plaster in that it's all very sharp edged and apparently pretty brittle. Gypsum plaster really hates damp even though it seems to attract it!

It would be interesting to know the exact nature of the render and masonry paint. In the early days parts of my stone house were repointed in a 1:1:6 cement lime mortar and that hasn't caused any problems that I'm aware of. Problem cement mortars are usually very hard, cement lime mortars quite a lot less hard, lime mortars usually soft and are not prone to shrinkage cracking once set. Unless there are other signs of subsidence those cracks are more likely to be shrinkage which might indicate a cement harling. I'd definitely be wary of any cement filling that's been done of cracks and gaps in the raised stonework on top of the gable end.

I do think you are correct to start with the easiest fix which is to cowl the chimneys, and vent the roof space. If you don't have fireplaces then the flues won't be vented and the salts of combustion in the flue could well be causing problems when washed through that wall.

 

[Lacan07]

Thanks Aockenden. This is what it looks like:
View attachment 12907

Does this look like cement rather than lime? What did you do after you stripped the cement from yours - just re-point? Is there any other solution than to take it off? Removing it is not really feasible for us due to the size of the house…

That looks like cement to me and even if it was lime the paint looks like something impermeable and plastic, it's certainly not limewash. The roughcast gives it away, I'm not sure if that was a thing with lime.

I walked passed a small row of shops with flats above situated within a very old building in Alton last year, there was a builder outside removing all of the cement render. I asked him why and it turns out he had only been hired to renovate the flats above but when they stripped the wall upstairs (gable end) it was sopping wet. The render didn't look bad but had obviously failed due to cracking, the owner had to pay him to remove it all and redo.

 

[stuart45]

That's not a cavity, just the normal gap between the stretcher bricks on a solid wall that haven't (for whatever reason) been filled with mortar.

It's not normally filled when building because it tends to make some of the stretchers belly out a bit, unless you stick dry mortar in the centre joint (known as the wall joint). It's particularly an issue when building a 9 inch wall built totally, or mainly with stretchers.
In theory the wall should have solid joints throughout, as voids allow moisture to sit in there.
On house walls, when only one side was face work and the inside plastered, it was quite common to increase the width of the wall joint to the width of your fingers to make it easier to lay the bricks when coming inside to run in the inner skin. This lead some people to believe that finger cavities were an early form of cavity walls, but in reality they were built as solid walls. Early cavity walls in the mid 1800's still had 2-3 inch cavities.

 

[Stevers]

'Harling' is a Scottish thing - it should be a mix of lime and aggregate applied as a slurry.
https://en.wikipedia.org/wiki/Harling_(wall_finish)
Ironically it doesn't require paint to protect a building.
No more than 20% OPC should be added, or it becomes a problem, as found out when an OPC harling was used on one of Macintosh's buildings in the 1900s.