Damp in floor where there was a fireplace

[timmo26]

Hello All.

Would really appreciate help on this. We have recently moved in to a 1930s house, which has has a fireplace removed at some point, see outline on floor: https://lh6.googleusercontent.com/-7SJp3efPLX8/T5lNr94zWNI/AAAAAAAAAFo/2BCis6Kum_0/s677/IMG_0099.jpg

There has been a bit of damp coming up through the joints between the newer grey concrete, and the original red screed.

I have pulled up quite a bit of the concrete to find the remainder of the chimney breast, etc.: https://lh6.googleusercontent.com/-...I/AAAAAAAAAGw/q1ZtUYNCj3g/s508/photo+(39).JPG

In between the two ends of the chimney breast is just some sort of loose hardcore packing, which is dampish, but not sopping. As far as I can see, the red screed also has hardcore packed under it, but no DPM or anything like that. There is no obvious damp coming through anywhere else on the floor, but the floor does show high damp readings.

Mainly I'd like to know if anyone can tell me what I should do to fill in where the fireplace was, so that I don't get damp coming up through the floor again, i.e. so I can decorate the room and get on with things.

Thanks for any help,

Tim

 

[stem]

I'm not sure if this is 'professional' solution, but I overcame the same thing in the dining room of a 1960's built house I purchased 17 years ago.

I had rotten floorboards over the fireplace area which were laid on timber sitting in the damp hardcore and a black (because of mildew) section of skirting / wall. I opened up the fireplace, dug down below the blue brick damp course, removing the wet hardcore / soil. I then lined the hole with a single piece (without any joints) of blue DPC plastic, filling it in with concrete which when hardened, I painting the top with rubber damp-proof paint before reinstalling the wooden floor on top. Finally I bricked up the fireplace opening in the wall and installed an airbrick to ventilate the chimney. There has not been any damp since.

In your photo I don't see any airbrick in the fireplace. This is necessary to prevent damp by allowing some airflow through the unused chimney. Also if the chimney top is not capped properly rain may be coming down the chimney causing the damp.

 

[timmo26]

I'm not sure if this is 'professional' solution, but I overcame the same thing in the dining room of a 1960's built house I purchased 17 years ago.

I had rotten floorboards over the fireplace area which were laid on timber sitting in the damp hardcore and a black (because of mildew) section of skirting / wall. I opened up the fireplace, dug down below the blue brick damp course, removing the wet hardcore / soil. I then lined the hole with a single piece (without any joints) of blue DPC plastic, filling it in with concrete which when hardened, I painting the top with rubber damp-proof paint before reinstalling the wooden floor on top. Finally I bricked up the fireplace opening in the wall and installed an airbrick to ventilate the chimney. There has not been any damp since.

In your photo I don't see any airbrick in the fireplace. This is necessary to prevent damp by allowing some airflow through the unused chimney. Also if the chimney top is not capped properly rain may be coming down the chimney causing the damp.

Hi Stem, thanks for replying.

It sounds like what you did is more or less what I was thinking that I would do.

But there are some differences. The chimney breast has been removed all the way up to the loft, so there's no water downstairs from the chimney; it's all in the floor.

Also, I'm concerned about where the ends of the DPM would go. Did you just take it to floor level and cut it off, or lay it across the floor? Wouldn't this solution run the risk of just forcing the moisture up around the membrane, and therefore just moving the damp?

That's what I can't get my head around.

Thanks again.

Tim

 

[stem]

I had exactly the same concerns about the moisture coming around the sides.

My chimney was capped and the chimney itself was dry, so I assumed that the damp was being drawn up through the soil & hardcore like a 'wick' rather than the water itself actually coming up that high. I thought that if the natural water level was above the damp-proof course I would be in a lot more trouble than I was and that the whole wall or house would be damp not just the fireplace area

I only mentioned checking that the damp wasn't coming down the chimney from above as a possibility as you didn't mention it. A lot of rain can come down an open chimney pot.

What I dug out was dripping wet BTW.

Once the concrete was dry I cut off the protruding plastic with a Stanley Knife before painting over the top with the waterproof paint.

By coincidence, I also lowered the chimney below the roof line, but only because I wanted matching bricks for a small repair elsewhere.

Like I said I can't say if this is the best method or not, but it worked in my case. The wall has been papered for the last 10 years and it's stuck fast with no sign of damp on the wall, skirting or floorboards.

 

[timmo26]

Thanks again Stem.

I have dug down a bit further, to find a layer of rough brick lying on the bare clay. The bricks are damp, but not sopping, and the hardcore that I dug out was generally fairly dry.

I think what I'm going to do is dry out the hardcore, then bung the bigger bits back in (not the sand, as I think it will go down the cracks and wick up the moisture).

I'm then going to make up some concrete with Sika-1 waterproofing additive (apparently nothing gets through Sika), and bung that in the hole. I can't decide whether to use a DPM, as there isn't one on the rest of the floor, and I'm not even entirely sure that there's a DPC in the brick.

Once I've done all this, I'm going to paint over it with a water-based epoxy, and hope for the best.

However, as this is a party wall, I'm a bit concerned that maybe it's next door who have some sort of leak going on in their fireplace, which is causing our problem.

Any thoughts on that?

 

[stem]

I can't profess to be an expert in these matters, just someone like yourself that tries to fathom out what a problem is and how to overcome it.

My chimney walls had two rows of engineering bricks as a damp-proof course the bricks below that were wet and those above were dry, so I concluded that the loose rubble filling the centre was 'wicking' the wet up. In your case, if the hardcore is sitting in wet soil, then I would assume that it will wick it up too, so would address that anyway. If that doesn't solve the problem then could be the time to worry about what's happening next door. Although I would imagine that if you have damp from them, their situation would be much worse and prompt them to take action.

I didn't have that consideration as my home is detached.

 

[gregers]

dig it all out and lay some joists in with wall plates where needed,make sure you have good underfloor ventiltion,jobs a gooden no more damp.