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Concrete Hearth for Lopi 1750i

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by REDSLED88, Dec 9, 2012.

  1. REDSLED88

    REDSLED88 New Member

    Joined:
    Dec 9, 2012
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    Alright, so I'm new here, so go easy (LOL)

    What I'm doing is installing a Lopi Republic 1750 insert. My current hearth does not meat the 16" clearance in front from non-combustibles.

    Right now I have approx. 11" of hearth, which is stone approx. 1" thick.

    So, I've pulled the carpet back exposing the red oak hardwood floor under carpet and infront of existing hearth. I assume this is 3/4" thick.

    What I'm proposing to do is remove the 1" stone, and then cut back the 3/4" thick hardwood down to the subfloor, to create an area for a new hearth. (approx. 42" wide and 28" deep).... approx. 1 3/4" thick.

    My question is:

    I want to pour a concrete hearth. Can I just put some tar paper down, and put a layer of lathe down on top of the subfloor? Then pour an approx. 3" thick by 42" wide by 28" deep concrete slab on top of the lathe?

    Is this ok for code? The specs. I've found for a 2012 Lopi Republic 1750i say nothing about R value in front of the stove or hearth area. They only say "non-combustible material".

    Would this hearth be sufficient for non-combustible?

    An approx. 3" thick slab will yeild a hearth 1 1/4" of increased height.
    I'm affraid to install a 4" thick hearth, as the weight may be too heavy for the subfloor.

    I don't want to do tile, or stone or anything else. I'm going to do a concrete slab and acid wash
    to match existing 70's beige/brown/red flags in mantle.

    Also, I live in California, and the regulations are getting out of control, so I though I'd nip it in the bud and start here.

    I will call the County on Monday and find specs. for them, but wanted to run this by the forums first.

    Will post pics tomorrow,
    Thanks in Advance,

    TIMK

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  2. begreen

    begreen Mooderator Staff Member

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    Non-combustible is just that. If you had just 1/4" of cement it would be adequate.
  3. REDSLED88

    REDSLED88 New Member

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    Fewwww... I was hoping you would reply!
    I just wanted to confirm that the Lopi Republic 1750i had no R-value specifications?

    Should I put Micore 300 down first maybe for added protection? Then pour my slab (hearth) on top of that?

    My second concern is that a 3" thick concrete hearth (slab basically) will be really heavy in this area.
    At 42" wide by 28" deep by 3" thick it will weigh approx. 306lbs.

    I don't think I want to do anything less than 3" because structurally it will be weak, and can possibly crack

    Thanks again begreen!

    TIMK
  4. begreen

    begreen Mooderator Staff Member

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    Correct, the 1750 only needs a non-combustible hearth. I know little about concrete or it's structural needs. Best to ask a mason that question.
  5. suprz

    suprz Member

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    Rhode island
    I would also be wondering about the weight, but if you are from california, you dont have a basement to worry about, probably just a crawl space under the house? If so maybe just put footings under that area of the subfloor. I am originally from california so i know about crawlspaces..too bad your house isnt on a slab, you could just cut back the carpet and be done.
  6. Treacherous

    Treacherous Minister of Fire

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    WA state
    Would a hearth extension be an option for you if the concrete hearth won't work?
  7. REDSLED88

    REDSLED88 New Member

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    Yeah, just a crawlspace, but it would be a bear cat to go under there even to just re-inforce between joists. Its on the otherside from my crawlspace opening, and I don't think I could get any materials (piers, concrete, and lumber) back there... just too tight.

    I wish I could just go with say 2" of concrete over Micore 300.... but my mason says that it wouldn't be structurally strong enough... especially if you may split kindling in that area, or have multiple people stand around the fire.

    Yes, a hearth extension would be an option, if they didn't look like $*%#.


    I'm going to go back over today (new house, just purchased on 12/5/12.... first house BTW).
    I've got a bunch of other things to do over there, and I may just run it by some other options.
    Maybe new stone over Micore... basically extending the hearth from 11" to 28".
    I would be afraid that stone will weigh just as much as concrete.

    Thanks for all the replies..... keep the options coming.
    I'll post some pics and let everone know what I do.

    TIMK
  8. Bunsen

    Bunsen New Member

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    Nov 3, 2012
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    I just tore out a hearth and built a new one for my new 1750. My requirements seem less substantial than yours as I am not planning on using an axe to split anything on mine. I used durock (1/4" concrete board) with a layer of unmodified thinset under it on the subfloor. then 6x12 tile stuck down with modified thinset. All layers add up to about 3/4" of noncombustible material which is even with the finished floor. I also sistered the actual 2x6 floor joists with modern 2x6 to make sure the floor is very stiff under the stove.

    3" of concrete would be pretty heavy, plus another 400 lbs of stove on top of it. Plus wood if you keep some on the hearth. I don't do this sort of work for a living, just as a homeowner who can't always pay someone else to do it. In my opinion, pouring a concrete pad may be easiest, but there are probably ways to do this where weight wouldn't be a worry.
  9. begreen

    begreen Mooderator Staff Member

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    I would install something more attractive and less utilitarian. It will vastly simplify the project, will look better and will enhance resale value. Save the wood splitting for outdoors. A nice stone, tile or brick extension can be done so that it looks entirely intentional. If you can post some pictures of the existing hearth we may be able to offer more specific suggestions.
  10. alden

    alden New Member

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    There's no reason you couldn't pour a thinner slab. People pour concrete countertops all the time that are about 2 inches thick. You have to use steel reinforcement (welded wire mesh not lath, and maybe poly fibers), and select a smaller agregate size to do it,but it can be done. I know you said you don't want stone, but a nice stone slab would have the strength you want (depending on variety) and you could lay it over the top of your floor and not have to cut out your oak which would be a shame imo. With out seeing the area you want to do this in it's hard to give an accurate opinion though. I wouldn't worry too much about the weight either. If you have anything 2x6 or bigger and they don't span great distances, then you might be surprised at how much they support. Don't forget anything laying flat is distributing weight so you have to consider how much weight per square foot your floor can handle. Alot of lumber yards have structural consultants on their payroll. It costs nothing and they can help with issues just like this. Is the existing hearth part of an acutual fireplace, if so then that area should be framed for heavy masonry loads, I doubt adding a few inches off the front of it will hurt anything.

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