# DuRock or Hardibacker 500



## bowhunter3714 (Dec 27, 2007)

I'll be up loading a picture in a few days of the construction area for the stove. We have a storm coming in tonight and I'm going to go buy the cement board today to start the floor layout. 
Question: Which is better for using under tile, which the stove will be sitting on?
DuRock 3'x5'x1/2" or Hardibacker 3'x5'x1/2" Thanks for the quick repiles.


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## Harley (Dec 27, 2007)

Assuming Hardibacker is something you could use and it would pass inspection, I would use that.  It is a hell of a lot easier to cut and handle than durock, and makes much less of a mess.  I think there is some debate as to whether or not it would be accepted.  I'd check with your BI first.


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## nshif (Dec 27, 2007)

Duroc is better as it is speced by the manuf for use in hearths. Hardi is somewhat non commital on its product but has worked for many people. Micor is beter then either but hard to find in some areas


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## begreen (Dec 27, 2007)

Durock has no fillers, Hardibacker does have some cellulose fillers. My tile guy said he won't use Hardibacker, even if it's easier to work with.  Micore is entirely different. It's insulation, not an underlayment. 

BH, what is the plan for the hearth? What is the plan for the walls?


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## DriftWood (Dec 28, 2007)

Hardy backer is made of cellulose; I called James Hardie technical support 1-888-JHARDIE about the lack of R value off their ½ inch hardybacker product. They told me ½ inch hardybacker has no Rated R value,* “it conducts heat”*. Hardy backer is not the stuff you want behind your stove or under it. WonderBoard or Durock cement boards are R rated and UL Listed for that application. I’ve only used Durock brand board because it is 100% cement with a fiberglass backing.

# note
1/4” hardi backer board is R=0.13 per for specs check out this web link to conform fire resistance and r-value

http://www.jameshardie.com/homeowner/products_backerboard_halfInch.shtml 



*MICORE® Brand 300 * 
r-value 1.09 

http://www.acoustics.com/specs/USG_product/usg_spec.pdf#search=’micore 300 spec’ 

MICORE® Brand 300 Board from USG is a superior substrate for fabric and vinyl-covered wall panels, office 
dividers and tack boards. An excellent core for chalkboards,* stove boards* and similar applications, MICORE Brand 
300 Board offers outstanding resilience, superior machinability, high “k” factor, heavy density and highest surface hardness of any MICORE 

*½” Durock *
r=.26 

http://www.usg.com/USG_Marketing_Co...ts/DrckCement_Board-Submittal_Sheet_CB399.pdf 

Composition and Materials DUROCK Cement Board is formed in a continuous process of aggregated portland cement slurry with polymercoated, 
glass-fiber mesh completely encompassing edges, back and front surfaces. The edges are formed 
smooth—patent No. 4,916,004. The ends are square cut. 

Description 
DUROCK® Brand Cement Board provides a smooth, sound base for glass and ceramic mosaics; ceramic and quarry 
tile; lugged tile; and thin stone and thin brick. Suitable for application to wood or steel framing spaced 16 o.c. in 
new construction and in remodeling. Board is ideal for use in partitions, walls, floors, soffits and ceilings in wet or 
dry areas. It does not deteriorate in the presence of water so it is highly durable in high-moisture areas such as 
baths, showers, kitchens and laundry rooms. Also adaptable for fences, fireplace fronts, mobile home skirting, 
agricultural buildings,*UL-listed wall shield/floor protectors*, garage wainscoting and exterior finishes. 

Limitations 
A. DUROCK Cement Board is designed for positive or negative uniform loads up to 50 psf. For complete information 
on the use of DUROCK panels in exterior systems, consult your USG sales representative. 
B. Maximum stud spacing: 16” o.c. (24” o.c. for cavity shaft wall assembly); maximum allowable deflection, based 
on stud properties only, L/360. Maximum fastener spacing: 8” o.c. for wood and steel framing; 6” o.c. for ceiling 
applications. 
C. Maximum dead load for ceiling system is 7.5 psf. 
D. Steel framing must be 20-gauge or heavier. 
E. Do not use drywall screws or drywall nails. 
F. Do not use 5/16"DUROCK® Brand Underlayment for wall or ceiling applications. 
G. Do not use DUROCK Cement Board with vinyl flooring.


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## webbie (Dec 28, 2007)

I agree with Drift. Hardie could probably get a listing if they tested, but they have not done so, so I would only use the listed products. After all, just the fact that one cuts a little easier is no reason to go off-spec.


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## bowhunter3714 (Dec 28, 2007)

I should have pics up this afternoon. Moderator, the Hearth size will be aprox 10' x 11' and the walls will will be Durock with a 1" air space (if relocate plugin) or 3" air space if I don't. Have not decided on that yet. Will it matter as long as I have at least a 1" clearance? You'al see why in the pics. Thanks for everyones input and Driftwood, thanks for the links. I bought 2 ea 3'x5'x1/2" sheets of Durock to start my layout pattern on the floor. Again thanks.


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## webbie (Dec 28, 2007)

I don't think 1" or 3" will make a diff as long as stove clearance to the original combustible wall is maintained. This is 12" min. if using NFPA or possibly closer (or further) if your manual specifically addresses this wall protection.


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## bowhunter3714 (Dec 28, 2007)

Heres a pic. Location to be installed. I called insureance company again and had them did deeper into the clearance issue for me. I can go as close as the manual states as long as I have my Durock installed between the stove and the wall. Some questions:1. Which would allow more heat into the living room, in the corner as pictured, centered on back wall, or slid over closer to the right will? Or would it really matter. I'm would like to have room for logs in the left corner.2. If in corner the instructions read Corner distance from combustible wall at 11". If centered on back wall it reads 18 1/2 ". This seems to me a little close even with Durock up but 36" takes up a lot of room. Any input on this, Thanks.


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## begreen (Dec 28, 2007)

What's most important is the orientation of the ceiling joists that the support box will be mounted between. To a certain extent that will determine the stove location within the clearance limits. 

This stove doesn't list any close clearance specs, so the extra wall protection is more for your own peace of mind. 15" (B) is the Century back clearance spec. 18.5" (E) is from the flue connector to the wall.  36" is not required. That is for an unlisted stove. The corner clearance I'm reading (C) is 12" minimum.


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## webbie (Dec 28, 2007)

Yeah, looks like there is no reason other than style to do ANYTHING on the wall.
You can save a lot of time and money just installing it as per the manual.


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## bowhunter3714 (Dec 29, 2007)

BeGreen, your spec's  and the sheet that came with my stove are a little different. Which is right? My sheet reads the following:

A Sidewall 18 1/2
B Backwall 14
C Corner 11
D Sidewall 24 1/2
E Backwall 17 1/2
F Corner 17 1/2
G Ceiling 57 3/4


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## webbie (Dec 29, 2007)

Bow, check two things:
1. The label on your stove
2. The model number and then look for the newest brochure and manual online....

I'll let BG answer the other part.


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## begreen (Dec 29, 2007)

I should defer to the one that came with the stove. The sheet I posted came from online. But I like it better, it's a bit more conservative. 

Regardless, the backwall clearance is a long way from 36". If it were me I'd go with the newer spec. There's no penalty for exceeding specs. They are just the minimums. And actually, the centerline location of the flue pipe may be the final determinant. If your ceiling support box adds an inch or two away more than spec from the wall, then go with it.


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## webbie (Dec 29, 2007)

If the model numbers are exact and there are different (by a pretty wide margin) clearances, then you might want to call CFM customer care and get the right scoop on it.


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