The mystery of the damp wall

[Quaintcottage]

I have a large patch of damp in my cottage . I recently purchased the property , aware that it had flooded 25 years ago. See photo.



The wall is a party wall; the other side is my neighbour’s fireplace . I was told by my surveyor that the likely cause of the damp was a fault with the neighbour’s chimney , or the flashing around it . No problem I thought , I would just move in and pay for the flashing or chimney to be fixed, end of.

I have had a roofer look at the flashing on my side and he said it is not in a condition to cause the associated damp below . I have spoken to my neighbour who said the Chimney was repaired ten years ago and really does not think it is at fault. I was about to push hard against this assertion when I noticed two man hole covers outside the window , adjoining the damp wall.



Both had water at the bottom and one had a submersible float pump that pumped water out of the hole when the float was activated .



I had another conversation with the neighbour who said they were connected to French drain type pipes that were laid under the house before it was tanked 25 years ago, apparently their role was to divert water from under the concrete floor to these holes, and if the water table rose , the water would be pumped away from the house .

I am now looking at my damp wall and wondering if the cause is the water trapped under the floor that is finding a route up into the party wall . I thought the party wall was Cornish stone , my neighbour thinks it is COB.

Could water trapped under the tanked floor cause damp shown in the first photo? How would this be remedied?

I guess I am in a predicament. I have a small amount of funds left to try and investigate and fix the problem . I originally thought I would just plow it into the roof and/or chimney , but I don’t want to do that, and exhaust my funds and find out , the problem is under the house and have no funds to fix it .

Please do let me know if you have any experience or this type of damp . Any advice would be appreciated.

Thank you

 

[paulc]

I am now looking at my damp wall and wondering if the cause is the water trapped under the floor that is finding a route up into the party wall . I thought the party wall was Cornish stone , my neighbour thinks it is COB.

If the walls are cob, the last thing anyone wants to do is tank the stuff. Seen way too many reports of cob building collapse after they had been rendered with cement.
I think you need to investigate the construction of that wall before making any decisions on cures.

 

[Quaintcottage]

Thank you Paulc. I believe the property was tanked 25 years ago ; I will certainly look to clarify what material that wall is made from .

 

[malcolm]

The photo is typical for a waterproof wall with gypsum plaster and emulsion paint on top. You wonder how that much water can possibly be getting into the wall. Often there isn't all that much water trying to escape from the wall but after 25 years it starts to build up.

The way to sort it tends to be to hack off all the non-breathable plasters and paints and get back to whatever the wall is made from that is presumably breathable and wants to dry out. Then re-plaster in lime and wait a year or two for the damp to go away. The wall won't be cob if it is supporting a chimney. If the chimney is not in use it should have a vented cap. Just rain falling down the chimney will be enough to cause damp when you have tanking.

 

[Quaintcottage]

Thank you for your reply . I doubled checked the survey ; they took samples from each wall and you are correct the Party Wall is stone not COB.

I spoke to my neighbour and he does use the Chimney albeit only in Winter. It has a bird guard on top but nothing to prevent the water coming down the Chimney

I will take your advice and remove that section of plaster in the next week or so. I am having an asbestos survey next Tuesday to test the plaster , before I start to remove it . If I am lucky , it will reveal a beautiful Cornish granite stone wall , which I might keep .

I spoke to the surveyor who originally surveyed the house before purchase, and who identified the damp; he said he can come back and look into the damp issue a little closer and maybe help me understand where the damp is coming from .

I am conscious that I can go down a road of paying ££ for various surveys and just get opinions as opposed the answers.

 

[malcolm]

Presumably you will have once had a fireplace too sitting beside or behind next door's fireplace. It wouldn't be too surprising if the strangely square damp spot conceals a fireplace opening. If the fireplace next door is in occasional use any moisture getting into that would evaporate away into their house and your side would be dry.

Surveys probably won't be much very much help - at best they can't see anything you can't, and at worst they'll want to sell you expensive retrofit waterproofing. I would be chipping off the plaster to see what is there.

 

[Quaintcottage]

Thank you for your reply . A roofer who was surveying the property this evening thought I might have once had a Chimney, like you suggest . The shape of the damp patch is definitely in the shape of a fireplace.

I have an old chimney on the opposite side of that room , as I have a huge open fireplace .

It is very hard to get an accurate history of the property. The solicitors think it was built cc 1800s. It was added as an exstension to the neighbouring cottage , and used to be owned by the members of the same family.

It looked to me like they had just added three walls to the property next door and made a new cottage. Although my roof was replaced in 2011, the original rafters were not replaced , and for some reason , my cottage was built about a foot lower than the neighbouring cottage.

I will go into the loft tomorrow and see if I can see any evidence of a chimney. The damp patch is on the party wall between the two properties in the attached photo.

I tend to agree with you with respect to surveys , they can quickly become a money pit.

Thank you

 

[Quaintcottage]

Per Malcolm’s advice , I removed some of the plaster to allow the wall to dry. The neighbour has confirmed there was once a a Rayburn and chimney where the damp patch is now located .

Behind the plaster was a stone wall with one loose red brick which worked itself free when I was chipping at the plaster . See photo.

I am guessing the brick was placed there to close up the gap where the Rayburn’s flu attached to the Chimney . That is a big guess

There was a cavity space behind the brick then cement and what looked like layers of slate. Maybe they back filled the chimney with slate or tiles?

Is it safe to have a gap in the wall? I have no experience of load bearing and supporting walls.

 

[Quaintcottage]

For reference, this is the offending brick

 

[Stevers]

It's very low to be for any sort of flue for a range. It might I suppose have been for a gas fire if you have gas, but it is exactly where someone might put an airbrick to vent a redundant chimney. We have stainless steel cowls with bird mesh on our two live chimneys. These are good for the chimney as a whole and will keep any lining in better condition. Worth considering offering this to your neighbour as an upgrade at no cost to him.

What I think may be significant is that water appears to be running down that wall, pointing to condensation. It's not impossible that this is a cold spot that 'sweats' in the summer months. It would be better if this wasn't able to just sit on the surface of the wall. Those of us with original stone floors will be aware that in conditions of warmth and high humidity our lovely cool floors can sweat too. I'm currently keeping an eye on the flagstone floor of a basement alcove. This has been bone dry all winter and spring and then about six weeks ago it has developed quite an impressive damp spot - a candidate for 'grump of the day'!

 

[Cubist]

Stevers, in drawing attention to the apparent stains of water running 'down' the wall and his thoughts on 'sweating' stonework has me thinking that perhaps the source of the moisture may be somewhat higher up the wall than first thought. I'm thinking that, as this house was built as an extension to the neighbouring property, the builders simply butted the then new fireplace into the extant chimney breast to establish a communal flue. When that fireplace was removed its possible that the old entry into the communal flue was not effectively closed. This may then result in rainwater penetration from the neighbours flue or, possibly, the creation of a cold void behind the wall which in turn causes atmospheric moisture produced inside that room to condense out on the higher section observed.

I'm probably barking up the wrong tree here but it may be worthwhile hiring a good quality borescope to investigate the void behind the brick you've already removed.

 

[Quaintcottage]

Hello Stevers and Cubist , thank you both for your replies.

I am leaning towards condensation being the primary cause of the damp. The damp has always been more apparent the few times the central heating has been on , or my partner has had a bath. I initially thought there must be a leaking water pipe , but there are no pipes anywhere near that wall.

Stevers, I think you are correct with respect to the cold spot theory , as are you cubist with your cold void idea. My neighbour’s fireplace is the other side of that wall, and I might have a hidden fireplace and /or communal flue, within the wall; airflow to both of these will surely make the wall colder and create a cold spot, and attract condensation as I heat the room?

A number of people have noted that the shape of the damp in the initial photo, is that of a fire place.

I am going to ask my neighbour if he remembers my property having a separate chimney. I have noted before that there is no evidence in the loft of an old chimney on that side of the house . I have also pondered why the damp patch suddenly started to appear higher up the wall.



I like the idea of a bore scope but I can see the back of the void and it is filled with mortar and what looks like bits of slate . I am not keen to start drilling or chiselling away at it for fear of what I might uncover .

I think I will have to spend the next few weeks testing some ideas. I will whack the central heating on tonight and pray for some rain and monitor what happens.

 

[Cubist]

Pardon the pun... but an 'off the wall' thought occurs when reading your last.

We all enjoyed a very mild winter last and during that our use of the wood-burner that services our CH system was much reduced. This radically altered the typical airflows throughout our home and, whilst nothing obviously detrimental arose there were observable instances of greater/lesser condensation than might typically be expected and not always in the usual suspect areas.

Did you perhaps change your heating habits during that period or made other changes that may have altered the usual air current patterns?

 

[Quaintcottage]

Hi Cubist. I have only lived at the property for a few months. Prior to June the cottage was pretty much empty for about 6/7 months ;

it was used an AirBnB prior to my purchase. I would take an educated guess that there was not much air flow in the property prior to me moving in .

The damp in the wall was pretty bad when I moved in during June. If you compare the two photos you can see I have managed to dry the wall out during that period.

 

[malcolm]

Does the air smell damp when you put your nose through the hole? I had a chimney that was capped at the top and it had a tree growing out of it. I vented the top and the tree died (because the chimney dried out). It wouldn't do any harm to find out how the disused chimney is capped and add a bit of ventilation at the top.

It would be tricky to remove the chimney if it is attached to the chimney next door so there's a fair chance there is a hole on top of the chimney stack letting water in, or a blocked off hole up there. Else you'll see it in the loft and can vent it there (being careful of carbon monoxide risk if next door's chimney is leaky).

 

[Quaintcottage]

Hi Malcom , no it does not smell damp. I lit a candle next to the hole in the wall to see if the smoke would be draw into the hole but it was not.

I am still guessing that the hole was put in to vent the old chimney . I have looked in the loft and there’s no evidence a chimney was ever there, but my neighbour insists there was once a fireplace and an old Rayburn exactly where the damp wall is . His family once owned both cottages and he used to sleep in the said room as a child.

I was expecting to find lots of modern bricks blocking the entrance to an old fireplace , but the wall is solid stone with that one random hole cut out.

I do like a mystery but I also want to get on and decorate that room

 

[Stevers]

Presumably the staircase is not original, because of it was, a Rayburn sited there would really get in the way. The two chimney flues next door could be for upstairs and downstairs or back and front rooms. A chap was walking up the road when we were working on our chimneys and asked why we had ten chimney pots. The answer of course was that our house once had eight fireplaces, a (small) kitchen range and a copper in the scullery, so there's plenty of scope for two flues to be needed on the end of a house..

 

[Quaintcottage]

A bit of an update 6 months on .

Forum member Malcolm was correct:

“Presumably you will have once had a fireplace too sitting beside or behind next door's fireplace. It wouldn't be too surprising if the strangely square damp spot conceals a fireplace opening.”

I was lucky enough to find some old plans from the 1980s when my cottage was renovated . The plans clearly show a fireplace on the party wall. See photo



A separate plan from 1988 clearly states that the fireplace is to be removed and the opening blocked . See photo



The previous owner was unaware that there was once a fireplace behind the party wall, as he purchased it many years after the above renovation work . He did say that the damp on the aforementioned wall , started when next door relined their chimney . Prior to this , smoke from next doors chimney made it into the loft in my property .

6 months ago , I think forum member Cubist hit the nail on the head when he said

“I'm thinking that, as this house was built as an extension to the neighbouring property, the builders simply butted the then new fireplace into the extant chimney breast to establish a communal flue. When that fireplace was removed its possible that the old entry into the communal flue was not effectively closed. This may then result in rainwater penetration from the neighbours flue or, possibly, the creation of a cold void behind the wall which in turn causes atmospheric moisture produced inside that room to condense out on the higher section observed.”

I need to now work out how to resolve the issue. I have drilled into the wall with a 1foot drill bit and I have not found any voids to pin point the fireplace , which makes me think they did a very good job filling it .

The brick blocking what I presume was a vent for the old fireplace has been removed . All the old wet plaster has been removed back to what is now concrete , and I have painted that section of wall with damp proof paint . There has been no damp since I have taken these steps , but I am aware that my neighbour has had his wood burner going the other side of this wall , for the last few months , and as someone above pointed out , the damp could return in the summer months .




Should I lime plaster the wall now and wait and see , or are there other things I should investigate first?

 

[Cubist]

Hello again and thanks for the update.

Prior to this , smoke from next doors chimney made it into the loft in my property .

That information suggests that the mortar work of the chimney was in a poor condition at the time and, while that problem may have been addressed, it may be an idea to verify the conditions of the masonry in the loft space if at all possible.

I'm also assuming that the 'lining' installed by your neighbour was associated with installation of a stove or range and its worth noting that if there is an opportunity for rainwater to enter via the chimney pot or any weakness around the top of the chimney this can and will flow down the sides of the liner to appear on the surface of the walls in the interior of the building - I sometimes see just such a problem when the prevailing wind direction changes here. In your case though any remedial measures would be entirely at the pleasure of your neighbour.

I'm afraid therefore you may be at the 'suck it and see' stage of things and should perhaps just get on with plastering the wall.

 

[Quaintcottage]

Hi Cubist, thank you for your reply. The previous owner , explained to me (after purchase) that some years ago, he smelt smoke in the loft; it could only have come from next doors chimney, there is no chimney stack in the loft - see photo above. Next door then had their chimney lined and that stopped the smoke seeping into this property. The lining process was explained to me as a cast in place liner . I have copied this text from another website

"flue casting or cast in place is a process that involves placing an inflatable rubber form down inside a masonry chimney casing and pouring a specialized insulating cement around it. The material is thin like pancake batter and is poured to a minimum of 3/4″ around the form as its vibrated. Upon completion you have a new flue passage and a re-enforced chimney casing. We perform this work."

(https://fcpros.com/product/flue-pas...e casting or cast in,the form as its vibrated.)

The previous owner explained it as : next door put a balloon down the chimney, poured concrete around it, then deflated the balloon, and the chimney lining was completed sealed.

It now occurs to me as i write this : that if my now sealed in fireplace , shared the same chimney flue, then the above lining process might have blocked the hole in the chimney my fireplace was using to vent air/smoke into the shared Chimney. If my thinking is correct, does that mean I have a lot of damp air , that is unable to vent through the chimney and can only find a way out through the aforementioned damp wall?

Apologies if my reasoning is a bit jumbled up. I am off to watch some rugby so my replies will be delayed until this evening. Many thanks for the input.