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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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  1.  
    Hi all


    I have an old stone and brick fireplace and will soon be having a multi fuel stove stove installed. There are a handful of gaps between bricks, some of which are quite deep. I'm now finishing the prep and there's a few things I'm not sure about and wondered if anyone can help please?

    1. The constructional "hearth" in the recess could do with a lick of paint. Any suggestions as to what paint would be best to use? The fitter said emulsion should be ok, but a little googling seems to suggest emulsion isn't so great with high temps. I should add we are having a Woodwarm Fireview with no legs. So the ashpan section of the stove is in direct contact, although I won't really need to paint directly beneath the stove; just the visible parts to the side and front...

    2. There's the odd gap in the pointing, some of them very deep (150mm). I'd like to fill them before the stove goes in but I'm not sure what' best to use and whether it needs to be heat resistant? Saying that, I've no idea what the existing mortar repairs and pointing were done with?!

    3. One of the side walls is covered in "black stuff". I'm happy with the aesthetic; in fact I like it. But could it potentially cause any problems? If so, I'm thinking best to remove it now while I can...

    Photos below.

    Thanks a million
  2.  
    Photo 1
      01 Fireplace  Small.jpg
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    Photo 2
      IMG_20210201_095009665 (2)  Small.jpg
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    Photo 3
      IMG_20210201_145619265  Small.jpg
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    Photo 4
      IMG_20210201_145649313  Small.jpg
  6.  
    Sorry if that was a daft way to add the photos, but nothing else seemed to work...
    • CommentAuthorphiledge
    • CommentTimeFeb 4th 2021
     
    The black stuff is almost certainly soot/tar from a previous open fire. Over time bits will probably drop off but as the stove area will likely be dirty anyway, you may not be bothered??

    Theres what looks like the end of an old wooden lintel on the left of the fireplace that probably needs removing to get combustible materials away from the fire??

    Theres plenty of heat resistant paint around which my be a bit more durable than emulsion. Id imagine normal brick mortar would be fine for filling the gaps, but if you want a smooth finish you could line the recess with cement fibre board like Hardibacker and paint it black- thats what we did after the original skimmed render fell off!!
    • CommentAuthorgreenfinger
    • CommentTimeFeb 5th 2021 edited
     
    Hi there

    Many thanks for the helpful reply :)

    Yes, we're not bothered if bits fall off. The mess isn't a problem, and if it changes the look, well, then that's all part of the fireplace's journey through time! The wooden lintel is far enough away from the stove and twin wall can be used to get passed it. Thanks for pointing it out though.

    One of the paints we've found is a clay paint by Earthborn. Quite pricey though, but we'll only need a tester. I'll take a look at other heatproof options.

    We definitely want to keep it as is, so won't be rendering. Just need to fill / repair a few gaps. I'm glad you think a basic mortar will be ok, as I've been reading about lime based mortars but they take a long time to dry, and time's something we don't have!

    I've read through the Q&As on this page and the chap says this is not suitable around fireplaces:

    https://www.screwfix.com/p/cementone-general-purpose-mortar-grey-5kg/36857

    I can't work out if the ready made mortars in tubs like that are literally just cement and sand mixed, or if there's more to it?! If we mix our own...

    - What's the best ratio?
    - What type of sand?
    - Do I need to use a plasticiser or any additives?

    Also, would it be best to ram bits of stone or similar into the gaps so that they're not as deep?

    Many thanks

    PS - I can post some photos of the gaps if that would help?

    Thanks @philedge for your help, and to anyone else who joins in :)
    •  
      CommentAuthordjh
    • CommentTimeFeb 5th 2021
     
    Posted By: greenfingerOne of the paints we've found is a clay paint by Earthborn.

    That's what we have on all our walls. It's good stuff with good coverage, but do watch out for pencil marks. In the odd place our carpenters had put some lines on walls, which the paint covered but then after a while they show through again. So I might be careful about covering soot etc. No idea about its heat-resistance.

    You can buy heat resistant mortar, or there are DIY recipes on the net if you search.
  7.  
    Thanks for that tip.

    I have seen heat resistant mortars but they don't seem suitable. I think they are for in actual fireplaces. Our stove body maxes out at 230C. So the walls should be a fair bit lower than that. Yet the heat resistant mortars are ok up to 1400C. A tad overkill I thought. On top of that, this one:

    https://shop.vitcas.com/vitcas-heatproof-mortar-10kg.html

    Says "It is also not suitable for use as a rendering or gap filling material."

    Cheers
    • CommentAuthorphiledge
    • CommentTimeFeb 5th 2021
     
    Your walls arent going to get much above warm with all that thermal mass to heat up and conduct the heat away, so I wouldnt get too hung up about getting the perfect mortar for your application.
    • CommentAuthorrevor
    • CommentTimeFeb 6th 2021
     
    I plastered internally with lime render and painted with Earthborn paint, Have run stove for 2 winters now and the paint and plaster still looks like new. We allowed the plaster to dry out for at least 6 months before painting and refitting the stove. The stove shop said that lime plaster was the best and as we were doing the stone walls with it we did inside the reveal at same time. Alternative is to line with a fire board I think there is one made specifically for this situation but have no experience of it.
  8.  
    Excellent, thanks guys.

    The lime plaster is out as we only have a week. And we really like the aesthetic so would rather not hide it behind any fire board. See as we are only do a handful of repairs, I think I'll go with the basic mortar mix. I can't find out whether to use sharp or builders sand - there's a lot of conflicting info out there! So I'm think to compromise and hedge my bets with 2 part BS, 2 part SS, 1 part OPC. And possibly a dash of plasticiser. Then everyone's pleased :)

    Hopefully it will be fine. If it all goes wrong and what we do and/or what's existing falls out, then worst case scenario we can have the stove removed in the summer and do a proper job; removing ALL existing mortar repairs and pointing and redo with lime based mortar. The actual wall itself (ie not in the recess) we will definitely point with lime mortar when the time cometh.

    @revor - that's good RE the Earthborn paint. How close to the stove is your paint? Is it in any way translucent or totally opaque? I have been reading more about people having success with emulsion. And what we're aiming for is rough and ready so it doesn't have to be a perfect finish. That being said, my ultimate would be to get it looking like natural stone but I've no idea how to achieve that. In fact, I'm not even sure if it is a stone slab or just a concrete base. we don't like the colour of it as is (light grey) and so would still want to dye it, seal it, enhance the colour somehow, and with that comes considerations of heat and flammability and what the heck to use...

    Thanks for all the help :bigsmile:
    • CommentAuthorrevor
    • CommentTimeFeb 7th 2021
     
    The stove closet distance is 100 mm on one side and 300 from the back. Paint is opaque but I guess the darker colours will be more opaque. I used white and a pale yellow but they were going on a light coloured background i.e. lime plaster. Sounds like you are going to paint the bricks so you will need to remove as best you can the soot residues I would also prime the surface with SBR.
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