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question on hearth fllor

Post in 'DIY and General non-hearth advice' started by georgepds, Jan 28, 2013.

  1. georgepds

    georgepds Member

    Joined:
    Nov 25, 2012
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    So I've decided on an insulated floor for the progress hybrid stove, and I have a question about how to fix one layer to another. I decided on the following pattern and would like some feed back on how to fix the layers one to the other.. (BTW.. if I'm all wrong about the approach, please let me know and suggest alternatives)

    1/4" tile
    1/2" cement board (durock)
    1/2" micron 300
    24 gage sheet metal
    3/4 " plywood

    First some notes on why I choose what. The tile is for show and for an incombustible surface. The cement board is for a hard back for the tile, and a bit of thermal resistance (R~0.2) . The micron 300 is for most of the thermal resistance ( R~1.0) . The 24 gage sheet metal is to avoid hotspots, and the plywood is for support. I'm not sure the durock is needed.. it's there mostly because tile is normally laid on durock , I know you can lay it on the micron 300, but the guy I have to do tile has never done so before.


    Tile to cement boad is is done with mortar, and grout between tiles

    Cement board to under layment is done with durock screws.. but should some type of matsic be used? Also I think the screws should go all the way down to the plywood

    Micron to to sheet metal is durock screws again , and again.. some type of mastic?

    Sheet metal to wood should be roofing nails , and again .. some type of mastic

    comments appreciated

    --G

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  2. semipro

    semipro Minister of Fire

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    I'm no expert on this but it seems like overkill. The stone under my wood stove just does not get that hot and mine has the short leg option.
    The radiant heat from most stoves goes sideways or upward. Heated air obviously moves upward.
    The ashes in the ash pan (assuming you have one) actually do a fairly good job of insulating the hearth from the firebox.
    I think the tile with backer board will be more than enough.
    Again, I've not taken temps or built a hearth like you're doing so....
  3. georgepds

    georgepds Member

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    Hi

    Might be.. but the PH manula calls for an R =1 , the durock has an R ~ 0.2
    Adios Pantalones likes this.
  4. Adios Pantalones

    Adios Pantalones Minister of Fire

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    Semipro- practically speaking, you may be right, but its wise to stick to code for insurance and other reasons.
  5. semipro

    semipro Minister of Fire

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    Agreed. I would never advise doing less than code.
    Adios Pantalones likes this.
  6. semipro

    semipro Minister of Fire

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    This is interesting though.
    Both our stoves sit on top of a foot of masonry, one with wood beneath it.
    We may not be meeting code requirements of R 1.0.
    Crazy-- but I learned something.
    I'm definitely fulfilling my role here as "not an expert". ;)

    Edit: actually this code requirement starts making sense to me when I think about hot coals falling from the stove to the hearth.
    Adios Pantalones likes this.
  7. Adios Pantalones

    Adios Pantalones Minister of Fire

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    Ya, I guess they're meant to cover extreme circumstances and stupidity, not normal operation. Not that I ever do anything stupid. uhhemmm.
  8. begreen

    begreen Mooderator Staff Member

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    Screw down the Durock, thru the micore to the plywood per instructions (one special screw every 8"). No thinset or mastic between those layers.
  9. georgepds

    georgepds Member

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    Might not need R 1, The progress hybrid call for R=1 in the manual, but if you use the version with an "ash lip" this is reduced to R= 0.4... For reference here is what the woodstock soapstone company lists on their blog .. R values add .. double the thickness and you double the R

    material / thickness / r
    ceramic tile / 1/4" / 0.02
    cement mortar / 1/2" / 0.025
    cement board / 1/2 " / 0.26
    brick / 4" / 0.8
    Durock Next Gen / 1/2 "/ 0.39
    micore 300 / 1/2" / 1.03

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