Isolated DAMP issue on front elevation 1875 mid terrace (Yorkshire)

[migmags]

looks like a water leak to me, and there is a lot of water.

is it all round the house? higher in certain areas? or just in particular places? please stand back and take some wider pics, inside and out, and especially of the "highest point" of the damp, if there is one.

As you are in a terrace, I presume all the other houses were built with the same materials and techniques, at the same time. Are they all damp? Do they have damp patches, and do those patches coincide with, say, a kitchen, bathroom or downpipe?

does rainwater lie on the paving, or run towards the house wall?

please sketch the position of drains, gutter downpipes, gullies and manhole covers

and water pipes, sinks and taps, and especially the incoming supply pipe. Does it run under the hall floor? is the floor solid or wood with a ventilated void beneath? Is the floor wet?

have you got a water meter?

do you know where the outside and the inside stopcocks are?

do you have access to sharp young ears?

p.s.
why doesn't the condensate run into a drain?

Sorry, categorically not a water leak, without sounding dismissive. otherwise I'd have a damp and wet wall right now - and I don't.
As mentioned in original message - the issue appears during the cold winter period. That's it. It's currenty dry right now with just an existing tide line where it was previously wet.

 

[migmags]

I wonder if it really does have a cavity? I'd have thought too old, but am not familiar with this type of build.

it's possible for water to get into a cavity, and then soak into the builder's waste invariably found in it. it's a hard but rewarding job to clean out a cavity.

This may be a possibility - yes. Since there's a flue running through the wall beneath, it's possible that there's been work done in that area that required plastering - it appears to be pink plaster (Gypsum), I took the plug socket off to check.
if I knock the wall below the tide line, it sounds hollow-ish. Above the line -more solid, like solid wall. This may be where it's just filled with crap (?)

 

[migmags]

Drawing shows a cellar. Typically there will be a keeping (coal) cellar at the bottom of the steps which is the most common point of entry for incomers, although not always. Pre-1900 a lot of stone built terraces had stone flag floors, at least above the cellar. I have to admit that before posting I assumed thay the OP would have thoroughly investigated potential waste and water pipe leaks, including the condensate pipe, and stuff like downpipes, troughing, etc

It's a tanked out, fully functional living room with underfloor heating. Part of it is split into two storage "rooms" facing the front elevation - one is where the boiler is situated - and where the flue runs out towards the front (the damp area is above the flue).
The other room is just a storage room which has been partially boarded, but you can still see the old foundations etc - it's all dry down there.
I have had a boiler engineer check that the flue isn't leaking hot air, which I initially thought might be mixing with cold air in the wall and condensing on the outer part of the inner wall - it's all good, no issues.

 

[JohnD]

Sorry, categorically not a water leak, without sounding dismissive. otherwise I'd have a damp and wet wall right now - and I don't.
As mentioned in original message - the issue appears during the cold winter period. That's it. It's currenty dry right now with just an existing tide line where it was previously wet.

you don't find that water evaporates more quickly from a damp porous surface in hot, dry conditions, then?

i'd better close my tumbledrier shop.

 

[migmags]

you don't find that water evaporates more quickly from a damp porous surface in hot, dry conditions, then?

i'd better close my tumbledrier shop.

The damp meter is telling me it's "wet" when I check, however, it doesn't look like the picture I posted originally (that's from the winter). The dark section is now gone.

I'm just not convinced it's a leak, sorry.

 

[opps]

The damp meter is telling me it's "wet" when I check, however, it doesn't look like the picture I posted originally (that's from the winter). The dark section is now gone.

I'm just not convinced it's a leak, sorry.

Damp meters are useless for plaster, timber yes, plaster no.

From memory, when plaster gets wet, the salt composition changes and increases conductivity, even when the plaster is perfectly dry. A damp meter is akin to the continuity setting on a multi-meter.

 

[mrrusty]

The essential detail may be that this occurs when you turn the heating on in winter. Two things we can take from this - 1) warm heated air has the ability to carry more moisture than cool air, so it may well be that your moisture-load in winter with the windows shut is higher than summer. 2) As it's winter the bottom of the wall will be colder.

It's a fairly straightforward calculation. Get a hygrometer/thermometer and an infra red surface thermometer. One evening, take a humidity reading and room temperature after a full day of heating and normal living. In the morning, after a chilly night and after the heating has been off for a while, take a surface temperature reading of the base of the wall.

From the table for room temperature you can see the saturated vapour density which multiplied by the RH% gives the actual vapour density. Looking at the table you can see what the dew point is for that vapour loading (it's the corresponding temperature for saturation). If your wall temperature in the morning is lower than that, you are getting condensation on the wall surface

Say 25 degrees and 60% RH (yes warm and quite humid) the vapour load is 23 x 0.6 = 13.8 g/m3. The dewpoint for this vapour load will be about 16 degrees (from the table 15 degrees is 12.83).

If calcs show condensation is a risk, then the principal remedies are to avoid moisture-creating activities, improve ventilation and possibly get a dehumidifier.

And for the pedants - yes, I know technically relative humidity is the ratio of vapour pressures not vapour densities, but the calcs are virtually identical and it's easier to visualise/quantify grammes of water/cubic metre

 

[migmags]

The essential detail may be that this occurs when you turn the heating on in winter. Two things we can take from this - 1) warm heated air has the ability to carry more moisture than cool air, so it may well be that your moisture-load in winter with the windows shut is higher than summer. 2) As it's winter the bottom of the wall will be colder.

It's a fairly straightforward calculation. Get a hygrometer/thermometer and an infra red surface thermometer. One evening, take a humidity reading and room temperature after a full day of heating and normal living. In the morning, after a chilly night and after the heating has been off for a while, take a surface temperature reading of the base of the wall.

From the table for room temperature you can see the saturated vapour density which multiplied by the RH% gives the actual vapour density. Looking at the table you can see what the dew point is for that vapour loading (it's the corresponding temperature for saturation). If your wall temperature in the morning is lower than that, you are getting condensation on the wall surface

Say 25 degrees and 60% RH (yes warm and quite humid) the vapour load is 23 x 0.6 = 13.8 g/m3. The dewpoint for this vapour load will be about 16 degrees (from the table 15 degrees is 12.83).

If calcs show condensation is a risk, then the principal remedies are to avoid moisture-creating activities, improve ventilation and possibly get a dehumidifier.

And for the pedants - yes, I know technically relative humidity is the ratio of vapour pressures not vapour densities, but the calcs are virtually identical and it's easier to visualise/quantify grammes of water/cubic metre

interesting you mention this - my next course of action was to get a dehumidifier and have it in the general area where the issue is occurring and to see if the "dark" patch appears; i'm wondering if this might prove the same as your calcs - which would be worth doing too

 

[migmags]

The essential detail may be that this occurs when you turn the heating on in winter. Two things we can take from this - 1) warm heated air has the ability to carry more moisture than cool air, so it may well be that your moisture-load in winter with the windows shut is higher than summer. 2) As it's winter the bottom of the wall will be colder.

It's a fairly straightforward calculation. Get a hygrometer/thermometer and an infra red surface thermometer. One evening, take a humidity reading and room temperature after a full day of heating and normal living. In the morning, after a chilly night and after the heating has been off for a while, take a surface temperature reading of the base of the wall.

From the table for room temperature you can see the saturated vapour density which multiplied by the RH% gives the actual vapour density. Looking at the table you can see what the dew point is for that vapour loading (it's the corresponding temperature for saturation). If your wall temperature in the morning is lower than that, you are getting condensation on the wall surface

Say 25 degrees and 60% RH (yes warm and quite humid) the vapour load is 23 x 0.6 = 13.8 g/m3. The dewpoint for this vapour load will be about 16 degrees (from the table 15 degrees is 12.83).

If calcs show condensation is a risk, then the principal remedies are to avoid moisture-creating activities, improve ventilation and possibly get a dehumidifier.

And for the pedants - yes, I know technically relative humidity is the ratio of vapour pressures not vapour densities, but the calcs are virtually identical and it's easier to visualise/quantify grammes of water/cubic metre

Hi,
I thought I'd provide a quick update on this - especially the calculations you've provided. Tuesday evening I noticed the darker patch appear on the wall again - checked the thermometer/Hygrometer nearby and it was reading 70% humidity (we'd just finished having dinner etc..) at 19 degrees indoor air temp (i don't have a thermo gun to check the wall) BUT it was the first sudden drop in temp all year - with outside temps of 14/15 degrees. I used a dew point calculator and it spat out a number of 13.5 degrees, which correlates near enough to the outside temp and consequently the affected wall - of course, there must be a reason this section of wall is much colder and will need addressing.

So, this MUST then be the source of damp on the internal wall - there's no question about it that it's condensation related. The questions now remains of how to fix it.

Would I just need to cut out the affected area of plaster, dry it out and apply a thin interior wall membrane and reboard it, plaster over etc..?
Part of me is tempted to just try applying something like Zinsser Stain Killer and repainting to see what happens as a cheaper first option - and perhaps using a dehumidifier to remove some of the added moisture in the air.

 

[mrrusty]

You can't cure condensation with membranes and paint. There are only two things you can change to prevent it - the humidity - dehumidifiers and/or ventilation, and the surface temperature of the wall. This is what internal (or external) insulation does - because it passes heat energy slowly, it is likely that the insulated wall surface will be closer to room temperature and condensation can be avoided.

The problem to watch out for though, is if that warm room air can get behind the insulation it will condense IN the wall. This is obviously not desirable, so internally insulating a solid wall is problematic. I've internally insulated my 1902 ventilated cavity wall with good outcome, but don't have first-hand experience of insulating solid walls. I have my opinions (that don't involve any sort of damp treatment) but hesitate to offer definitive advice. Have a read here:- https://assets.publishing.service.g...attachment_data/file/1019707/iwi-guidance.pdf

and also https://www.heritage-house.org/damp...ed-consequences-of-solid-wall-insulation.html

 

[migmags]

Thank for the info - I've read a lot of Heritage House advice and share their feelings with the DPC industry, only just having had 2 quotes from these chancers; over 2k to strip the ground floor elevation to the brick 1m high, inject DPC and making good again - my eyes glazed over when they were giving me their "professional opinion" - citing "rising damp" as the issue. I politely escorted out of my house.

In terms of insulating the internal wall I would have no idea where to begin - my initial experiment with dehumidifier and a stain proof coat was to see if a less invasive approach was possible to begin with and if not, perhaps insulating (somehow) the internal wall second.

 

[migmags]

You can't cure condensation with membranes and paint. There are only two things you can change to prevent it - the humidity - dehumidifiers and/or ventilation, and the surface temperature of the wall. This is what internal (or external) insulation does - because it passes heat energy slowly, it is likely that the insulated wall surface will be closer to room temperature and condensation can be avoided.

The problem to watch out for though, is if that warm room air can get behind the insulation it will condense IN the wall. This is obviously not desirable, so internally insulating a solid wall is problematic. I've internally insulated my 1902 ventilated cavity wall with good outcome, but don't have first-hand experience of insulating solid walls. I have my opinions (that don't involve any sort of damp treatment) but hesitate to offer definitive advice. Have a read here:- https://assets.publishing.service.g...attachment_data/file/1019707/iwi-guidance.pdf

and also https://www.heritage-house.org/damp...ed-consequences-of-solid-wall-insulation.html

Thanks for the info - I've read a lot of Heritage House advice and share their feelings with the DPC industry, only just having had 2 quotes from these chancers; over 2k to strip the ground floor elevation to the brick 1m high, inject DPC and making good again - my eyes glazed over when they were giving me their "professional opinion" - citing "rising damp" as the issue. I politely escorted them out of my house.

In terms of insulating the internal wall I would have no idea where to begin - my initial experiment with dehumidifier and a stain proof coat was to see if a less invasive approach was possible to begin with and if not, perhaps insulating (somehow) the internal wall second.

 

[mordzy]

Just to chuck my two twopenn'orth in.

Rusty gives some great advice so worth following his recommendations.

My house is of very similar if not the same construction (West Yorkshire). I’ve spent years of research to concluded that modern materials and methods are not compatible with the design/construct of old houses.

A lot of the damp issues I have had have been resolved by reverting back to the original finish. In your house Ive observed a few issues.

1. Cement strap pointing. Traps moisture behind, causes spalling and possibly damp.

2. Gypsum plasterboard/skim. Stops the walls breathing.

3. Height of external ground.

How high is The ground outside? Is it above the internal floor. Perhaps install a French drain to allow water to soak away from the house.

It may or may not be rubble filled. I initially thought mine was, but in some places there is none, some have what I would consider builders waste which can hold water/moisture at the bottom of walls. This may contribute to your issue.

My suggestions.

Remove the plaster/plasterboard and inspect. Let it dry out. Remove a stone at the bottom and perhaps a meter higher and check for rubble/waste and clear out.

Chip off some strap pointing and inspect the joints, they usually go black and horrible behind if they have trapped mosture. Re point with lime mortar.

I don’t think it’s condensation as you usually get that high up, though vapour may be penetrating higher condensating behind and collecting at the bottom.

Essentially, strip back, investigate, repair in the correct way. Heritage house as mentioned above is an invaluable resource. They do do surveys but it’s not cheap.

Your dehumidifier will just be masking the issue and the paint will eventually come off, pushed off by the moisture from behind.

Ignore modern damp companies suggestions. If it’s not something you could tackle yourself, you need to find a builder who understands old buildings. There’s not many.


Perhaps post back your findings.

 

[migmags]

Just to chuck my two twopenn'orth in.

Rusty gives some great advice so worth following his recommendations.

My house is of very similar if not the same construction (West Yorkshire) and have I’ve mentioned hours and years of research concluded that modern materials and methods are not compatible with the design/construct of old houses.

A lot of the damp issues I have had have been resolved by reverting back to the original finish. In your Ive observed a few issues.

1. Cement strap pointing. Traps moisture behind, causes spalling and possibly damp.

2. Gypsum plasterboard/skim. Stops the walls breathing.

How high is The ground outside? Is it above the internal floor. Perhaps install a French drain to allow water to soak away from the house.

It may or may not be rubble filled. I initially thought mine was, but in some places there is none, some have what I would consider builders waste which can hold water/moisture at the bottom of walls. This may contribute to your issue.

My suggestions.

Remove the plaster/plasterboard and inspect. Let it dry out. Remove a stone at the bottom and perhaps a meter higher and check for rubble/waste and clear out.

Chip off some strap pointing and inspect the joints, they usually go black and horrible behind if they have trapped mosture. Re point with lime mortar.

I don’t think it’s condensation as you usually get that high up, though vapour may be penetrating higher condensating behind and collecting at the bottom.

Essentially, strip back, investigate, repair in the correct way. Heritage house as mentioned above is an invaluable resource.

Ignore modern damp companies suggestions.

Perhaps post back your findings.

Thanks for the reply - Yes, indeed stripping back is the ONLY way to know for sure.
To answer your questions..

1. Cement strap pointing. Traps moisture behind, causes spalling and possibly damp.
We've had a quote for this already - it was in excess of 7k as the entire house was done in this way - not much we can do. We may or may not end up doing it far in the future or make it someone else's problem if we sell later on. However, the rest of the house is fine and we're pretty good at ventilating the house.
2. Gypsum plasterboard/skim. Stops the walls breathing.
Yes, it is indeed Gypsum. I've checked. After stripping back I'll ask my plasterer to plaster with lime. However, do you know of a non-gypsum based plasterboard? What would suffice?

How high is The ground outside? Is it above the internal floor. Perhaps install a French drain to allow water to soak away from the house.
Not higher than the internal ground floor - you can see the images. The ground floor is below the window sill. We have considered this already but still not convinced it's water penetrating the exterior fabric.

As mentioned - the dark patch appeared on the first cold snap, even after the heavy rains recently nothing appeared. It may be as you say, warm air mixing with cold in the gap between the wall - interstitial condensation? Either way - insulating that part of the wall is key. I'm just not sure what the best way to do it is.

Thanks

 

[George_engineer]

Replacing the bottom 1m of plaster with an insulating lime plaster - something like this https://www.lime-green.co.uk/products/lime-plaster/ultra (plus top coat), could help. Lime plaster will deal with the humidity much better.

I had some reoccurring condensation damp on an internal wall. I replaced the bottom 500mm with lime plaster and that bit is perfect.... but annoyingly the gypsum plaster remaining just about is still showing damp/salt damage!