My Damp Hearth

[oursurveysaid]

In my 1880 Victorian End of Terrace, the relative humidity in my front living room is staying around 75%. Not good.

Part of the problem seems to be water ingress through the external flank wall (which used to be joining onto a house next door bombed in WW2). I'm hoping to cure that by having lead flashing installed on the roof instead of the cracked cement fillets, and probably removing all cement render and plaster from the wall, replacing with lime equivalents.

Today, I uncovered the old hearth area in front of the chimney breast, and found a bed of soggy clay soil. I'm hoping that it's only soggy from ingress rather than wicking up moisture from the ground.

What should I do? Should I did out the soil? Is there likely to be some sort of solid base to it or is it just a tunnel to the centre of the Earth?

Pics attached. Thanks.
Joe

 

[r896neo]

What level is the sub floor in other areas of the room? I assume there is more space under the joists outside the hearth area I hope so anyway as that very poor ventilation if not!?

If the subfloor is lower in other areas then your hearth may be a mix of weak concrete and rubble fill. I doubt its up to much.

In a house of your age the subfloor will not have oversite concrete of anykind obviously so of course the clay is probably damp it is bare earth and thats why your subfloor should be well vented.

If you have damp problems i would open up that chimney brest (or at least cut out that vent) and clear out anything in there and let it vent open for a while. Also make sure your air bricks are unobstructed and adequate.

These are both good things to do for long term building health even if not responsible for the damp so worth doing now when floor are exposed etc anyway

 

[oursurveysaid]

Thanks. You're right - the ground level is about a metre under the subfloor. Should I dig out all this damp soil and see what's underneath? It seems to just be packed earth rather than rubble or concrete.

Air bricks are fine. I'm hoping the dampness is just water coming down the chimney or trickling through the brickwork which should both be solved by my upcoming chimney and roof works.

I'm planning to install a wood burning stove in the fireplace once I've opened it up, but not really coming out into the room much. Will I need a hearth of some sort in this case?

 

[TheVictorian]

What is the other side of that wall, can you posty a photo of the ground. I had a similar problem and it was caused by the path sloping towards the house and water pooling against the wall when it rained. I relaid the path with a gradient away from the house and it was cured.

 

[TheVictorian]

You will need a hearth for the stove, last time I looked it had to project 300mm from the stove and be constructional (concrete under it). Check the regs though as I am no expert.

 

[oursurveysaid]

There's a concrete path. As the house used to be a mid terrace before WW2, the wall is my boundary with the house next door, so the path belongs to my neighbour.

The whole wall is cement rendered right down to the ground, and some idiots have injected DPC through the render. Theres a plinth thing on the bottom which is angled away a bit, so water seems to be running away quite well. As the render is cracked in a couple of places though, and is probably trapping moisture already present from defective cement fillets on the roof, I'm planning on having it taken off and probably lime rendered.

 

[r896neo]

Unused chimneys can be responsible for all manor of damp issues so opening it up and venting it fully is worth doing sooner rather than later to let it dry out a bit.

No need to dig out the soil too deep just get it well away from the joists and that sleeper wallplate on the photo looks pretty rotten. Ideally only create a constructional hearth the size you need so dig out the soil and make a basic box frame, line the base with a dpm and pour a small concrete slab. nothing too serious 4 inches thick would be fine.

 

[oursurveysaid]

Thanks for the advice, r896neo!

I've knocked part of the fireplace through, but am getting a bit nervous about the lintel/brick arch situation.

I can see this L-shaped strip of metalwork, but surely that's not supporting it?
Is it likely there's a brick arch in front of that concrete stuff above it?

My problem is the whole wall has been rendered in cement an inch thick! Tough to get off without damaging the brickwork too.

Any advice there?

 

[r896neo]

That angle iron could inded be the only support in there. Chimney brests are generally almost entirely self supporting and so the angle is only there to stop the immediate bricks above it dropping out. It has almost no structural load. You can happily carry on investigating without too much concern.

In a house of yours age there will have been an arch but this may have been removed or the angle used to lower the opening by building under the archbwhich may still be in place.

 

[oursurveysaid]

Thanks. Does the black stuff look familiar to you? It looks like it may be some sort of concrete lintel.
I was hoping it was just something on the back of the old brick arch to hold it together, but I can't see how there would be enough depth for the bricks to be there.
Think I'll have to just try and get through the rock hard render and have a look from the front. Very difficult to achieve carefully though!

 

[Doggit]

I've seen chimneys where the arch was there, and then a metal piece was a couple of courses higher, sort of belt and braces, but as arches are self supporting, it'd often depend on how shallow the arch was, as to whether it needed a metal support higher up.

How do you want the opening of the fireplace to be. If it's going to be square, will the opening be above the bar, or below it. If we assume the opening will be below the existing bar, then carefully cut in a brick out wither side at the top of the opening, put in a wickes concrete lintel that's 300mm wider than the opening, and put some mortar above the lintel, and then pack use pieces of slate either side to push up the lintel, then then cement it in.

As to the hearth, put some sand in the bottom of the hole, then put in a 1200 plastic dpm going up the sides, then fill with concrete. But you'll need to take out the joist nearest the chimney breast, as this wouldn't have been there when the hearth was originally built.

 

[oursurveysaid]

Thanks for all the great advice!

I will probably have the opening below the bar, as long as that gives enough height for a burner.

I had a reasonable quote from a fireplace installer who said he would also do the building work, though I may still have a go myself. What worries me is that the bricks above the angle iron are loose and falling out, so I'm worried about making the opening any wider without propping it up. As I don't have the tools for that, it's probably best to get someone in.





I'm digging out the soil in the hearth now, and worked out that it's 2 feet deep by hammering a metal pole into the soil. It's heavily compacted London clay soil, holding quite a bit of moisture, and I recognise the smell as being the same musty smell in the room when it's damp. In that case, should I remove it all right down to the solid (presumably concrete) base?

I've poked the subfloor with a stick and while it doesn't seem to be overpoured with concrete, it seems ash-like, very light grey, not like the soil in the hearth. Any idea what that would be? I also noticed lots of salt residue on the brick pillars supporting the joists. Do you think this will pose a problem, or is it normal in these sorts of houses?





I've had flashing installed on the roof now and it certainly looks like the dampness was/is coming from the chimney area, so hopefully removing the soil will get rid of the moisture leftover. (photo of the wall in front of the hearth)




Much appreciated,
Joe

 

[r896neo]

The salts are nothing to worry about. There is no need to dig out the hearth super deep as there will be no concrete under it most likely. Dig out to below the joists level to aid air flow in the sub floor and then form a box with scrap timber and line it with dpm and pour a hearth as mentioned. Dont make it hugely deep, 4'' is plenty but dont make it more than a foot or it will be so heavy it might gradually sink itself over the years.

 

[oursurveysaid]

Thanks. I definitely felt some sort of base (concrete or stone?) in the hearth when I hammered a pole into it though... Does that change your recommendation to dig out? I'm worried I'll be trapping moisture in the soil which will keep seeping into the brickwork. Relative humidity is still about 15% higher than other rooms in the house

 

[r896neo]

You most likely hit a large stone or perhaps a bit of the wall footing. If you get the soil well down below the joists and use a dpm then there should be no issue.

Is the sub floor ventilated properly? Ventilate well and let the area dry out. How long since the chimney was fixed?

Its almost a certainty that water was soaking the area from above, i.e the chimney rather than coming up like a magic spring from below. Water is not magic, it doesnt go uphill with major help such as big pressure and if your groundwater was under so much pressure it would flood your subfloor before creeping up your walls. True rising damp is almost a myth it is so rare and many people would argue its not real at all.