Mystifying damp issue

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monica357
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Joined: Tue 10th May, 2022 12:21 pm

Mystifying damp issue

Post by monica357 » Thu 9th Jun, 2022 2:34 pm

This is a really confusing problem, which seems unsolvable. I live in a purpose built maisonette built approximately in 1910. (Tried to add pics but am told they are too large)
It’s best to begin at the beginning!
Just before Covid I noticed an internal party wall showing minor signs of damp-paper starting to separate from wall and some plaster beneath starting to crumble. I used Solvite to paste paper back and this worked, but not around chimney breast area. My new neighbour happened to call round asking if I had damp issues as he had following a chemically injected damp course the previous owners had installed before he moved in. I had had no issues before that damp course was installed! I went the usual route and was diagnosed with rising damp! Unsure of this I hired an independent surveyor who advised on remedial treatment involving water inhibiting sand/cement re rendering on bare brickwork, but no chemical injection. I went ahead with this and also had a French drain installed on the opposite outside wall and some brick re pointing. That was in October 2021.
However, and this is the new issue-when I lifted up the carpets in preparation for the work there was a wetness on the floorboards on the edge of the constructional hearth-carpets/underlay all dry. The surveyor I had previously used suggested I open up the area and dry it all out and replace boards. On lifting several boards around the fireplace I noticed a damp joist around fire place near the constructional hearth, more on one side than the other. The dampness increased and decreased according to the humidity levels in the room. I use a ThermPro Monitor to measure the humidity.
I hired another independent surveyor in March 2022 who recommended either
a) leave suitable time for everything to dry out and then replace damaged woodwork, ensuring it doesn’t touch the constructional hearth or masonry and put a damp membrane on the ends. Or
b) remove the whole stone fire surround, installed 15 years ago, replace all the constructional hearth and then as a).
The fire surround is fixed with a special adhesive so would be a massive job to remove.
In May, I hired a carpenter to cut the floorboards touching the constructional hearth so I could open up the area around the hearth. I turned these so that the edges were facing the other way but still upwards and these still get wet even though the edges are no where near the hearth! The edges which now touch the hearth don’t get wet!
I have used newspaper to gauge any wetness in corners around fireplace and this has got wet, not soaked though. The wet joist on the left seems to have a pattern/shape of wetness; it’s not soaked through and continues to the middle of the floor and then stops. It is near but not against the constructional hearth. On the right side the joist near the hearth just has patches here and there but does not continue to the middle of the floor. It actually touches the constructional hearth. All other joists are fine.
I took off the top layer of the constructional hearth as it was crumbly but this does not seem wet.
There don’t seem to be any leaking pipes and the ground subfloor does not seem wet.
I have taken out a lot of rubble, bricks slates etc from under the floor but not all of it.
There are two airbricks on the opposite outside window wall. The room is about 15 foot long.
It may be worth adding that my neighbour investigated his issue and found he had a leaking mains pipe and had to have all his floor removed, floor dried out and a new floor installed! Whether this has any bearing on my issue I am unsure. I have also had the chimney swept and some re pointing of the chimney stack.
Can anyone advise me? I really want to resolve this and get on with some decorating.

CliffordPope
Posts: 731
Joined: Tue 16th Nov, 2010 2:57 pm

Re: Mystifying damp issue

Post by CliffordPope » Fri 10th Jun, 2022 7:01 am

monica357 wrote:
Thu 9th Jun, 2022 2:34 pm
In May, I hired a carpenter to cut the floorboards touching the constructional hearth so I could open up the area around the hearth. I turned these so that the edges were facing the other way but still upwards and these still get wet even though the edges are no where near the hearth! The edges which now touch the hearth don’t get wet!
I've often noticed this effect. Wood, plaster or wallpaper that has once been damp still seems to attract moisture from the air. I think the original damp must leach out substances from the underlying structure which are deliquescent so the damp becomes self-perpetuating.
Areas around chimneys and hearths are especially prone, presumably from chemicals present in soot or smoke, even from long ago. I've noticed this too in walls that don't have a damp course - soil seems to be deliquescent too.

There are neutralising products, which I've never found to be very effective.

a twig
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Joined: Sun 6th Oct, 2013 10:18 pm

Re: Mystifying damp issue

Post by a twig » Fri 10th Jun, 2022 12:50 pm

Alternatively it may be residual water in the timber finally exiting rather than new water being attracted, but as Clifford says, if salts were carried into the timber originally these would get left behind by any drying out and so make the timber more likely to absorb water / moisture in the future

Is the hearth on the party wall?

Cubist
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Location: Shropshire/Herefordshire Border

Re: Mystifying damp issue

Post by Cubist » Sat 11th Jun, 2022 8:25 am

For obvious reasons perhaps but you don't mention the heat sources in the room concerned and where these may be in relation to the observed patches of damp. Any heat source will draw cold air toward it creating a convection current which sheds water moisture as it rises. What heat sources do you have in the room and where are they located in relation to the damp?

malcolm
Posts: 1166
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Location: Bedford UK

Re: Mystifying damp issue

Post by malcolm » Sat 11th Jun, 2022 5:19 pm

I'm currently removing waterproof plaster tanking from the base of my downstairs walls in an attempt to get rid of the last damp troubles. Though I suppose if you waterproof to a higher level than the neighbour then maybe the water will go their way. Often there isn't really much water to get rid of, but it you don't let it out somewhere it will rise until it finds an exit.

Wet joists are a worry. Joists suggest you have a void under the floor. That normally works really well - the timbers are off the ground and any water in the bricks will disappear with the underfloor ventilation. Ventilation is normally a few air bricks in the outside walls placed above ground level that allow some air circulation so you get rid of the damp before it gets to the joists.

Can you post photos somewhere else and include a link to them?

Lacan07
Posts: 32
Joined: Thu 15th Apr, 2021 5:11 pm

Re: Mystifying damp issue

Post by Lacan07 » Sun 12th Jun, 2022 7:57 am

monica357 wrote:
Thu 9th Jun, 2022 2:34 pm
This is a really confusing problem, which seems unsolvable. I live in a purpose built maisonette built approximately in 1910. (Tried to add pics but am told they are too large)
It’s best to begin at the beginning!
Just before Covid I noticed an internal party wall showing minor signs of damp-paper starting to separate from wall and some plaster beneath starting to crumble. I used Solvite to paste paper back and this worked, but not around chimney breast area. My new neighbour happened to call round asking if I had damp issues as he had following a chemically injected damp course the previous owners had installed before he moved in. I had had no issues before that damp course was installed! I went the usual route and was diagnosed with rising damp! Unsure of this I hired an independent surveyor who advised on remedial treatment involving water inhibiting sand/cement re rendering on bare brickwork, but no chemical injection. I went ahead with this and also had a French drain installed on the opposite outside wall and some brick re pointing. That was in October 2021.
However, and this is the new issue-when I lifted up the carpets in preparation for the work there was a wetness on the floorboards on the edge of the constructional hearth-carpets/underlay all dry. The surveyor I had previously used suggested I open up the area and dry it all out and replace boards. On lifting several boards around the fireplace I noticed a damp joist around fire place near the constructional hearth, more on one side than the other. The dampness increased and decreased according to the humidity levels in the room. I use a ThermPro Monitor to measure the humidity.
I hired another independent surveyor in March 2022 who recommended either
a) leave suitable time for everything to dry out and then replace damaged woodwork, ensuring it doesn’t touch the constructional hearth or masonry and put a damp membrane on the ends. Or
b) remove the whole stone fire surround, installed 15 years ago, replace all the constructional hearth and then as a).
The fire surround is fixed with a special adhesive so would be a massive job to remove.
In May, I hired a carpenter to cut the floorboards touching the constructional hearth so I could open up the area around the hearth. I turned these so that the edges were facing the other way but still upwards and these still get wet even though the edges are no where near the hearth! The edges which now touch the hearth don’t get wet!
I have used newspaper to gauge any wetness in corners around fireplace and this has got wet, not soaked though. The wet joist on the left seems to have a pattern/shape of wetness; it’s not soaked through and continues to the middle of the floor and then stops. It is near but not against the constructional hearth. On the right side the joist near the hearth just has patches here and there but does not continue to the middle of the floor. It actually touches the constructional hearth. All other joists are fine.
I took off the top layer of the constructional hearth as it was crumbly but this does not seem wet.
There don’t seem to be any leaking pipes and the ground subfloor does not seem wet.
I have taken out a lot of rubble, bricks slates etc from under the floor but not all of it.
There are two airbricks on the opposite outside window wall. The room is about 15 foot long.
It may be worth adding that my neighbour investigated his issue and found he had a leaking mains pipe and had to have all his floor removed, floor dried out and a new floor installed! Whether this has any bearing on my issue I am unsure. I have also had the chimney swept and some re pointing of the chimney stack.
Can anyone advise me? I really want to resolve this and get on with some decorating.
I'd echo the comments above, timbers in old houses can play tricks on you, especially if they've been exposed to leaks / moisture historically. Salts pull the moisture from the air. I also experience tiny wet patches appearing randomly in the boards around my hearth, and when I first cut access into my lofts I had a mini panic inspecting the roof structure! Old, rusty nails in particular seem to draw moisture form the air.

With regard to air bricks make sure they are installed at opposite sides of a room to ensure proper airflow under the floor

88v8
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Re: Mystifying damp issue

Post by 88v8 » Sun 12th Jun, 2022 10:28 am

monica357 wrote:
Thu 9th Jun, 2022 2:34 pm
(Tried to add pics but am told they are too large)
Hello and welcome

You can embed pics from an external site such as Photobucket.

There needs to be airflow beneath the floor. Air bricks on one side must be matched by airbricks on the other side. Any walls in between must be honeycomb so as not to impede airflow. Airbricks on one side only are near useless. Piles of debris may be a problem.

Sleeper walls under the floor, the little walls that support the beams that support the joists, those walls should be honeycomb and need to incorporate a damp course.

1910... I would have thought the house would already have a damp course, probably slate?

Your chimney breast... is it shared with the neighbour? Is it used by both of you? If not, are the pots capped to keep rain out, but not sealed so as to impede airflow? Is the flue open at the bottom or has the fireplace been blocked up with no air vent?

Damp brick and stone takes about one month per inch thickness to dry, once the cause of the damp is removed.

Ivor

MatthewC
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Location: Central/South England
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Re: Mystifying damp issue

Post by MatthewC » Mon 13th Jun, 2022 3:03 pm

Hi Monica

Here's my two pen'orth: first, did either of your surveyors have any qualification re old buildings? Or were they the dreaded DPC salesmen who just pretend to know what they are talking about when all along they are going to recommend their product/service, i.e. extensive DPC, cement and modern chemicals etc? "remedial treatment involving water inhibiting sand/cement" also sounds worrying.

Second, "I have taken out a lot of rubble, bricks slates etc from under the floor but not all of it. There are two airbricks on the opposite outside window wall." You need to get rid of all the stuff under the floor, check the airbricks are clear (one of mine was blocked by concrete!) and put some vents in the floorboards as far as you can from the airbricks. BTW, how much clearance do you have between the ground and the floorboards?

Third, "my neighbour investigated his issue and found he had a leaking mains pipe"! You might think that this does not still affect your house but it could. It takes a very long time to dry out an old house, and I suggest that you concentrate on getting the underfloor space ventilated and then wait for a while. You cannot hurry this process - I thought that my indoors was dry when I moved in after months of work and a hot summer but the following year I could see signs where door panels had shrunk after I had painted.

Matthew

Lacan07
Posts: 32
Joined: Thu 15th Apr, 2021 5:11 pm

Re: Mystifying damp issue

Post by Lacan07 » Mon 13th Jun, 2022 6:54 pm

MatthewC wrote:
Mon 13th Jun, 2022 3:03 pm
Hi Monica

Here's my two pen'orth: first, did either of your surveyors have any qualification re old buildings? Or were they the dreaded DPC salesmen who just pretend to know what they are talking about when all along they are going to recommend their product/service, i.e. extensive DPC, cement and modern chemicals etc? "remedial treatment involving water inhibiting sand/cement" also sounds worrying.

Second, "I have taken out a lot of rubble, bricks slates etc from under the floor but not all of it. There are two airbricks on the opposite outside window wall." You need to get rid of all the stuff under the floor, check the airbricks are clear (one of mine was blocked by concrete!) and put some vents in the floorboards as far as you can from the airbricks. BTW, how much clearance do you have between the ground and the floorboards?

Third, "my neighbour investigated his issue and found he had a leaking mains pipe"! You might think that this does not still affect your house but it could. It takes a very long time to dry out an old house, and I suggest that you concentrate on getting the underfloor space ventilated and then wait for a while. You cannot hurry this process - I thought that my indoors was dry when I moved in after months of work and a hot summer but the following year I could see signs where door panels had shrunk after I had painted.

Matthew
Vents in the floorboards is a good idea Matthew, I never thought of that, think I'll be utilising that in my house.

May I ask, what's your take on insulating under the floor in an old house? I'm of the opinion its not a great idea as moisture should be allowed to escape as easily as possible, but lots of people seem to do it and I can understand why. My sub floor can get a little damp after extended periods of rain. I'd thought about installing just a vapour barrier to prevent moisture rising into the house and rely on the air bricks (all new) to dry the floor, but I wonder if that's enough or how quickly / effective that would be. Apart from anything else i have no desire to get all the boards up and can't think of an entirely effective way to install a barrier membrane.

MatthewC
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Re: Mystifying damp issue

Post by MatthewC » Fri 17th Jun, 2022 3:50 pm

Lacan07 wrote:
Mon 13th Jun, 2022 6:54 pm
May I ask, what's your take on insulating under the floor in an old house?
I can only say that I didn't see the point and I have never noticed any issue with the ventilated suspended floor that I have. Make sure you put your floor vents where you make the best use of them - like in the opposite corner(s) to where the exterior vents are.

If you have the floor up then be sure to get rid of all the rubbish underneath. I found that I had stub joists that rested one end correctly on a wall plate (etc) but the other ends rested just on old broken bricks beside the fireplace! Not a long term solution.

I also had a supporting wall under the floor very close to the outside wall. Rotting floor boards had filled this narrow gap with debris, which rather encouraged dampness. I rebuilt the wall about 3" further back - and honeycombed to encourage ventilation, as Ivor said.

malcolm
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Location: Bedford UK

Re: Mystifying damp issue

Post by malcolm » Sat 18th Jun, 2022 7:41 pm

As Ivor (88v8) suggested the idea of the underfloor vents is to get a bit of air circulation to dry out any water that might otherwise make it's way up to the underfloor beams. Generally vents are placed on opposite walls and the wind blows air through and dries things out without disturbing the occupants above.

The idea of making an opening in the floorboards is new to me and I'm not aware of it ever having being incorporated into a building as built. Won't it give you a cold draught?

Should you be able to organise the underfloor drying out process so it happens completely underfloor then adding insulation shouldn't be any problem. Fibre stuff pinned on with netting better than the solid celotex stuff in case of drying failure.

monica357
Posts: 5
Joined: Tue 10th May, 2022 12:21 pm

Re: Mystifying damp issue

Post by monica357 » Thu 23rd Jun, 2022 1:15 pm

a twig wrote:
Fri 10th Jun, 2022 12:50 pm
Alternatively it may be residual water in the timber finally exiting rather than new water being attracted, but as Clifford says, if salts were carried into the timber originally these would get left behind by any drying out and so make the timber more likely to absorb water / moisture in the future

Is the hearth on the party wall?
Hi, The hearth is on a party wall.

monica357
Posts: 5
Joined: Tue 10th May, 2022 12:21 pm

Re: Mystifying damp issue

Post by monica357 » Thu 23rd Jun, 2022 1:18 pm

Cubist wrote:
Sat 11th Jun, 2022 8:25 am
For obvious reasons perhaps but you don't mention the heat sources in the room concerned and where these may be in relation to the observed patches of damp. Any heat source will draw cold air toward it creating a convection current which sheds water moisture as it rises. What heat sources do you have in the room and where are they located in relation to the damp?
One radiator on another side wall where there is no damp, well away from the hearth. Within the hearth there is a gas fire-coal effect in a basket-which I haven't used for well over a year .

monica357
Posts: 5
Joined: Tue 10th May, 2022 12:21 pm

Re: Mystifying damp issue

Post by monica357 » Thu 23rd Jun, 2022 1:28 pm

MatthewC wrote:
Mon 13th Jun, 2022 3:03 pm
Hi Monica

Here's my two pen'orth: first, did either of your surveyors have any qualification re old buildings? Or were they the dreaded DPC salesmen who just pretend to know what they are talking about when all along they are going to recommend their product/service, i.e. extensive DPC, cement and modern chemicals etc? "remedial treatment involving water inhibiting sand/cement" also sounds worrying.

Second, "I have taken out a lot of rubble, bricks slates etc from under the floor but not all of it. There are two airbricks on the opposite outside window wall." You need to get rid of all the stuff under the floor, check the airbricks are clear (one of mine was blocked by concrete!) and put some vents in the floorboards as far as you can from the airbricks. BTW, how much clearance do you have between the ground and the floorboards?

Third, "my neighbour investigated his issue and found he had a leaking mains pipe"! You might think that this does not still affect your house but it could. It takes a very long time to dry out an old house, and I suggest that you concentrate on getting the underfloor space ventilated and then wait for a while. You cannot hurry this process - I thought that my indoors was dry when I moved in after months of work and a hot summer but the following year I could see signs where door panels had shrunk after I had painted.

Matthew
Hi Matthew, They were both PCA surveyors -£200+ a time! When I first noticed a minor issue with the walls I did contact 3 damp proof companies who did say I had rising damp, but being sceptical I decided to go down the independent surveyor route before doing anything more. The 2 airbricks are clear. Unfortunately it's difficult to remove all the rubble etc as it would involve lifting up the entire floor which isn't practical at the moment as it's a through room. I have been reaching under the boards which I have lifted! sounds a bit pathetic doesn't it?There are 10 inches between ground and floorboards.

monica357
Posts: 5
Joined: Tue 10th May, 2022 12:21 pm

Re: Mystifying damp issue

Post by monica357 » Thu 23rd Jun, 2022 1:43 pm

88v8 wrote:
Sun 12th Jun, 2022 10:28 am
monica357 wrote:
Thu 9th Jun, 2022 2:34 pm
(Tried to add pics but am told they are too large)
Hello and welcome

You can embed pics from an external site such as Photobucket.

There needs to be airflow beneath the floor. Air bricks on one side must be matched by airbricks on the other side. Any walls in between must be honeycomb so as not to impede airflow. Airbricks on one side only are near useless. Piles of debris may be a problem.

Sleeper walls under the floor, the little walls that support the beams that support the joists, those walls should be honeycomb and need to incorporate a damp course.

1910... I would have thought the house would already have a damp course, probably slate?

Your chimney breast... is it shared with the neighbour? Is it used by both of you? If not, are the pots capped to keep rain out, but not sealed so as to impede airflow? Is the flue open at the bottom or has the fireplace been blocked up with no air vent?

Damp brick and stone takes about one month per inch thickness to dry, once the cause of the damp is removed.

Ivor
Hi Ivor, I can't undestand why I can't attach photos. I used a camera and they are worth seeing. I've contacted Simon, the admin chap but he hasn't got back to me on this. Anyway-I can't put airbricks on the other side as that's where the fireplace and chimney are on the party wall. The ones I have are on the only external wall in that room. Honey comb means spaced, does it? Well, they are in a row at the bottom of the wall and around constructional hearth-no gaps and joists sit on them. I think in the wet corner there are remains of a slate damp proof course but it's hard to tell. Chimney breast. Must be shared as neighbour's fireplace is on the other side of mine. I do use mine but not recently with these issues. Had chimney swept in December and my stack repointed in March. Because it is a coal effect gas fire a vent was installed in the floor for ventilation very near where the wet area is oddly enough.

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