Damp marks on fireplace hearth

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RushupEdge
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Joined: Mon 7th Sep, 2020 6:47 pm

Damp marks on fireplace hearth

Post by RushupEdge » Tue 8th Sep, 2020 10:09 pm

I recently bought a Victorian end of terrace and over lockdown have gradually been making progress with restoring it.

We ripped up the carpets in the dining room and noticed the floor boards were in a bit of a state with some breaking away. I should also add we had the house re-wired and central heating installed. The external patio has been laid too high (it meets the bottom of the airbricks) and we're in the process of taking the slabs away from the wall and digging a bit of a drainage trench until we can afford to re-pave.

With all that said, we've noticed that the hearth itself seems to have developed a few damp patches.

Image

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We pulled up the floorboards and managed to dig out lots and lots of sand and rubble that was piled up around the edges of the room and the front of the hearth. Some of the rubble in front of the hearth included lots of chunks of slate, which I'm assuming is the damp proof course...

It also looks like the front of the fender wall has collapsed or been broken:

Image

You can still see a bit of slate to the left of the image. At first I thought the white substance on the bricks might be mould, but having looked close I actually think it might be salt?! There are no signs of mould on the bottom of the floorboards, though there are a few damp stains in places.

We were due to have the hearth replaced and re-tiled as well as a fireplace reinstated - does this wall need to be re-built properly?

Could that be causing the damp in the hearth?

One more bonus question that could be related -

On the other side of the room we also noticed this issue -this is directly below our under stairs cupboard where our water and gas meter are. The light grey cables are the old electrics with the darker grey cables being the newer install.

As you can see, there seems to be a rather large damp area... This looks far bigger than just a condensation issue to me, but I can't hear any evidence of running water or a leak. Do you think I should get a plumber to investigate? or is this more likely caused by something else?

Image

Feltwell
Posts: 5632
Joined: Sun 18th May, 2008 7:28 pm
Location: Shropshire, England

Re: Damp marks on fireplace hearth

Post by Feltwell » Wed 9th Sep, 2020 8:49 am

I'm sorry but it's very difficult to comment properly from that post, but there are a few points.

Yes, the white stuff is salts not mould - so it's been wet, which dissolves salts within the bricks, which get left behind when the damp evaporates from the surface. Does the top piece of that wall need rebuilding? I really can't say, the bit you've pictured doesn't look great though and it certainly wouldn't hurt from the top section rebuilding with some damp proof course under the timber.

There will be nothing under the dirt beneath your floor, so it could be damp because of a leaking pipe, it could also be damp just from groundwater - but - if groundwater I'd expect to see general damp across all of it, not a localised area like you're showing. It would be sensible to check the pipes. The timber in the hearth picture is quite damp, damp enough that if it had been a long-standing issue hidden beneath a carpet, I would have expected the timber to have rotted - so I'm leaning towards it being a recent problem.

Have a good old peer around under there as a first step would be my advice - get a good light down there, see what you can, get an old phone or camera in video mode and tape it to the end of a stick and follow the pipes, see what you can see. One trick is to place plastic sheet below any areas that you suspect a pipe may be dripping, so it becomes more obvious if it does - some newspaper on top makes it even more visible and leaves a stain if it dries again - although bear in mind water can track along a pipe for a good way before it drips. Your new central heating, is it a combi boiler? Is it losing pressure? It's change that you're looking for, so a new heating system - and it looks like you've got the pipes for it up under your joists? - would be my first thing to check.

Hope that is of a little help at least!

steveb
Posts: 335
Joined: Sat 14th May, 2011 5:23 pm

Re: Damp marks on fireplace hearth

Post by steveb » Wed 9th Sep, 2020 10:48 am

it's also not unknown for plumbers to throw a lot of water about whilst installing systems (leaky joints, bleeding off into the floor void, etc) , so if you are lucky it will be a one off event that has yet to dry out - depends on how long ago the heating was installed I guess.

plasticpigeon
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Location: Birmingham

Re: Damp marks on fireplace hearth

Post by plasticpigeon » Wed 9th Sep, 2020 12:04 pm

The wood round the hearth looks like it has got wet from above not below. Was it covered with polythene for a while? If so could it be condensation from the polythene? I also had to rebuild the bricks below floor level in my hearth in what sounds like a very similar house to yours. A lot of my house was really thrown together, and there is evidence of botching in the original construction all over the place. Luckily construction with solid heavy bricks and lime mortar is very forgiving and accomodating of poor quality contruction. I also agree with Steve. If the plumbing was relatively recent then it could be water from those works which should dry out reasonably quickly. If you have rubble under the floors, have you checked that it is not blocking the airflow from front to back of the under floor space through the air bricks, eg the wall between the two main rooms downstairs should be honeycomb construction below the floor, and the sleeper walls should have gaps in them or honeycomb or at least have the spaces beween joists left empty for airflow etc.

RushupEdge
Posts: 13
Joined: Mon 7th Sep, 2020 6:47 pm

Re: Damp marks on fireplace hearth

Post by RushupEdge » Wed 9th Sep, 2020 12:10 pm

Feltwell wrote:
Wed 9th Sep, 2020 8:49 am
Yes, the white stuff is salts not mould - so it's been wet, which dissolves salts within the bricks, which get left behind when the damp evaporates from the surface. Does the top piece of that wall need rebuilding? I really can't say, the bit you've pictured doesn't look great though and it certainly wouldn't hurt from the top section rebuilding with some damp proof course under the timber.

There will be nothing under the dirt beneath your floor, so it could be damp because of a leaking pipe, it could also be damp just from groundwater - but - if groundwater I'd expect to see general damp across all of it, not a localised area like you're showing. It would be sensible to check the pipes. The timber in the hearth picture is quite damp, damp enough that if it had been a long-standing issue hidden beneath a carpet, I would have expected the timber to have rotted - so I'm leaning towards it being a recent problem.

Have a good old peer around under there as a first step would be my advice - get a good light down there, see what you can, get an old phone or camera in video mode and tape it to the end of a stick and follow the pipes, see what you can see. One trick is to place plastic sheet below any areas that you suspect a pipe may be dripping, so it becomes more obvious if it does - some newspaper on top makes it even more visible and leaves a stain if it dries again - although bear in mind water can track along a pipe for a good way before it drips. Your new central heating, is it a combi boiler? Is it losing pressure? It's change that you're looking for, so a new heating system - and it looks like you've got the pipes for it up under your joists? - would be my first thing to check.

Hope that is of a little help at least!
Thanks, that is indeed helpful.

We actually had the engineer who installed our central heating come and look at the problem yesterday - he couldn't find any issue with the central heating pipes, and the boiler hasn't lost any pressure from when it was installed so he was at a bit of a loss and suggested it could be rising damp. At that point I kicked him out :lol:

Our main water supply actually comes into the cupboard that is above that area of floor, so our next plan of action is to have a plumber see if he can find where the supply pipe is and check that for any leaks. I'm almost 100% sure that will be the original lead pipe, so it could be that perhaps. The only thing is I would have thought there would be more water or obvious signs of flooding if it was the main supply pipe.

Fender wall - Good to know that it's salts! Do you think this needs to be treated? I think we will need to replace that top brick course. We have someone coming to look at installing the fireplace so I intend to ask them about the hearth and see if the top course can be re-layed at that time. Do you think it's wise to use slate as the DPC on this re-lay or should a modern DPC membrane be used on this wall?

steveb
Posts: 335
Joined: Sat 14th May, 2011 5:23 pm

Re: Damp marks on fireplace hearth

Post by steveb » Wed 9th Sep, 2020 10:45 pm

I had a lead pipe once with the tiniest pinhole leak in, probably caused by other work in the vicinity disturbing it's peace. Certainly a candidate for investigation - leaving some plastic bags or newspaper about as above might help you narrow it down

Feltwell
Posts: 5632
Joined: Sun 18th May, 2008 7:28 pm
Location: Shropshire, England

Re: Damp marks on fireplace hearth

Post by Feltwell » Wed 9th Sep, 2020 11:08 pm

RushupEdge wrote:
Wed 9th Sep, 2020 12:10 pm
Fender wall - Good to know that it's salts! Do you think this needs to be treated? I think we will need to replace that top brick course. We have someone coming to look at installing the fireplace so I intend to ask them about the hearth and see if the top course can be re-layed at that time. Do you think it's wise to use slate as the DPC on this re-lay or should a modern DPC membrane be used on this wall?
No, salts are only cosmetic, ignore them. You can brush them off when it's dry if you want to. A modern strip of DPC would do the job just fine, it's continuous then.

Lead water main - yes, worth investigating, trouble is what investigation you can do is limited to what you can see. My money is on you having a leak somewhere!

RushupEdge
Posts: 13
Joined: Mon 7th Sep, 2020 6:47 pm

Re: Damp marks on fireplace hearth

Post by RushupEdge » Thu 10th Sep, 2020 4:23 pm

Feltwell wrote:
Wed 9th Sep, 2020 11:08 pm
RushupEdge wrote:
Wed 9th Sep, 2020 12:10 pm
Fender wall - Good to know that it's salts! Do you think this needs to be treated? I think we will need to replace that top brick course. We have someone coming to look at installing the fireplace so I intend to ask them about the hearth and see if the top course can be re-layed at that time. Do you think it's wise to use slate as the DPC on this re-lay or should a modern DPC membrane be used on this wall?
No, salts are only cosmetic, ignore them. You can brush them off when it's dry if you want to. A modern strip of DPC would do the job just fine, it's continuous then.

Lead water main - yes, worth investigating, trouble is what investigation you can do is limited to what you can see. My money is on you having a leak somewhere!
Great stuff, thanks for the advice!

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