1. Visiting from the US? Why not try DIYnot.US instead? Click here to continue to DIYnot.US.
    Dismiss Notice

Joints on hearth slabs cracking.

Discussion in 'Building' started by Soggy Bottom, 3 Jun 2019.

  1. Soggy Bottom

    Soggy Bottom

    Joined:
    12 May 2019
    Messages:
    33
    Thanks Received:
    1
    Country:
    United Kingdom
    I know this is an in the garden forum but this is the hearth in my living room. I put it here as it's still essentially paving slabs & the joints on them so figured it may be the best spot to ask this?

    Basically our living room suffers terrible damp. Those that installed the fire installed these black limestone paving slabs and from what i remember they put bonding in the mix which popped the front right flag up.
    They came out, re-did it with a sand and cement mix, no bonding this time. They also laid down a DPM. I can't remember whether it was wide DPC or whether it was visqueen. I've a funny feeling it was a fairly wide DPC. Obviously this was to stop the damp getting through since ours is quite bad.

    Photo 29-05-2019, 7 05 58 pm.jpg

    Now we've needed the fire out because of a separate ongoing issue but you can see there the joints have gone.


    Is there a way to stop that happening again or due to it being damp underneath, even with DPC strips there, and then the heat from the fire, it's just going to happen again & again & there's nothing you can do about it?
     
  2. Sponsored Links
  3. Ian H

    Ian H

    Joined:
    14 Sep 2010
    Messages:
    7,026
    Thanks Received:
    853
    Location:
    Rochdale
    Country:
    United Kingdom
    It looks a bit shallow to me.

    Could you raise it so there is a good thick layer of concrete under it?

    Or use 1 big slab?
     
  4. conny

    conny

    Joined:
    30 Jun 2008
    Messages:
    13,966
    Thanks Received:
    783
    Location:
    Suffolk
    Country:
    United Kingdom
    Is the floor below the slabs concrete or wooden suspended?
     
  5. Soggy Bottom

    Soggy Bottom

    Joined:
    12 May 2019
    Messages:
    33
    Thanks Received:
    1
    Country:
    United Kingdom
    1 big slab is something i've been thinking of. It would surely be have to cut to size though but it's something i've thought of. Not sure of material though. We went for black Indian limestone as we liked the look of it.

    I've just been & measured the bed and it seems to be 20mm in most places, 15mm in some. No idea if that's not thick enough or what.

    Regards the floor below the slabs - the living room is generally suspended timber floor however the hearth is on a stack of bricks which go in to the foundations. It's not actual brick under the flags. There must be some kind of material between the bricks & the flags but not too sure what it is.

    House was built early 1930s if that helps any with what it may be.
     
  6. Sponsored Links
  7. Munroast

    Munroast

    Joined:
    17 Aug 2010
    Messages:
    1,690
    Thanks Received:
    254
    Country:
    United Kingdom
    A full size slab would probably crack with the heat of the fire (esp if you use coal). That is why hearths are usually laid in two or three pieces, (our marble hearth is a 4 piece)

    As for the pointing coming loose - have they used a proper 'fire cement putty' ? if they skimped and just used regular cement then that fails pretty quickly.

    My guess is the damp has little to do with it .
     
  8. Mr Chibs

    Mr Chibs

    Joined:
    28 Jul 2015
    Messages:
    849
    Thanks Received:
    150
    Country:
    United Kingdom
    Some of the hearth could be on the suspended wooden floor, if this is rock steady all well and good.
    If there's a little spring/movement and mortar has been used, then you'll get cracking in the pointing.

    There could be a damp issue, as well, but probably not what's caused the problem you have.

    Presume you have a woodburner? Does it throw a lot of heat down to the hearth, so do some don't.
    I've one piece slate hearth 30mm and it's fine, but heavy, so less likely to suffer from flex/movement, especially when the weight of the burner is on it.
     
  9. Soggy Bottom

    Soggy Bottom

    Joined:
    12 May 2019
    Messages:
    33
    Thanks Received:
    1
    Country:
    United Kingdom
    That's exactly what's going down. The paving slabs have been taken out.

    Photo 16-06-2019, 7 28 25 am.jpg
    Photo 16-06-2019, 7 28 35 am.jpg

    I knocked out the old cracked cement and it had this layer of sand like stuff underneath in the middle.

    Regards fire cement putty, i don't think so. I'm pretty sure they sat it on a bed of sand & cement. I didn't think you'd sit paving on putty? I thought that was for things like around your windows? It's all over my head anyway.


    Yes the wood burner does kick out a fair bit of heat on to the paving slabs. After it's been going for a while & you touch them it'll burn your hand that's for sure.

    I don't think the hearth was on the suspended floor. Perhaps a little of the bed may have been but i didn't think it was. Difficult to tell, but there is flexion in the flooring, or at least there was in the old flooring and i don't imagine this would be any different.
     
  10. Soggy Bottom

    Soggy Bottom

    Joined:
    12 May 2019
    Messages:
    33
    Thanks Received:
    1
    Country:
    United Kingdom
    I just went looking for a brickwork forum but i guess this is probably the most suitable part? So may as well ask this here...

    Photo 16-06-2019, 1 49 37 pm.jpg

    I don't know what that chalky like coating is on the bricks. I'm guessing possibly what was left over from the dabs when we had boards attached to the walls. I can't get it off at any rate.

    We'll be leaving the wall exposed. I know you're not going to get a perfect looking brick as it's had stuff applied on top of it over time and it's an original 1930s wall but i was wondering if it'd be possible to get the chalky looking stuff off the sides? If so then how?
     
  11. DIYnot Local

    DIYnot Local

    Joined:
    3 Sep 2019
    Country:
    United Kingdom

    If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

    Select the supplier or trade you require, enter your location to begin your search.


    Are you a trade or supplier? You can create your listing free at DIYnot Local

     
Loading...

Share This Page