Hearth and Hardibacker

[WhatIsChazaq]

Seems like quite a hearty issue around here, I've used the search facility and have read for about 2 hours about this "question"...but some of the posts are a little older and seems like some q's were waiting for answers from James Hardie.

I have a ton (a little over a full pallet of the stuff!) of 1/2" Hardibacker in the garage - so I'm not so keen on having to go buy something else. I'm also not so keen on killing myself and my family because I didn't use a proper hearth material.

I have to achieve an R-Value of at least .59 for the VC Encore I just purchased.

My design so far is for three layers of 1/2" Hardibacker over 3/4" plywood and topped with 1/2" slate. That should get me an R-Value of .78 at minimum.

Would spacing the 3/4" plywood with strapping strips help or would that be a useless step?

Thanks a ton!

 

[edthedawg]

Call me conservative (and I'll laugh... no seriously...) but I'm gonna say you want to rethink your plan.

I wouldn't bother doing anything funky on the other side of your protective material (i.e. strapping under the plywood). I just don't like the cloud of suspicion around the HardiBacker product. I really prefer the Wonderboard / Durock concrete product vs the hardibacker, which allegedly (and my suspicious eye really is inclined to agree) has a cellulose component to its makeup. I keep a supply of building materials around too, but I would go back out and get the Wonderboard/Durock. keep in mind - I can't tell you how hot it gets under/around a fully-fired VC Encore... I had to go R 1.2 for the Heritage and yesterday I was measuring 200+ temps on the hearth tiles in front of and below the stove.

If I can ever find a dang torch, i'm gonna try a back-to-back-to-back flammability survey of Hardibacker vs. Wonderboard vs. sheetrock vs. anything else I can think of testing, and then post the results... Both of my torches have gone AWOL and i'm not gonna buy one just for this, as fun as it may be... (plus it's cold out - i'll be more inclined to play outdoors in the springtime)

FYI - I follow Tom's R-value guidance: http://www.chimneysweeponline.com/horvalue.htm - seems like you are using the same numbers.

Good luck and I hope others chime in - I'd love to hear results back from the Hardie company themselves!

 

[Jags]

....has a cellulose component to its makeup.

As does the "new" Durock. The new stuff is NOT hearth approved. This has been confirmed with a call to their product engineers.

 

[edthedawg]

"New" Durock?? Sounds fabulously crapulent. What'd they change??

 

[WhatIsChazaq]

Great...now on the search for Durock Classic...ala Coke Classic.

 

[begreen]

Both cement board brands (Durock and Wonderboard) say they have responded to the market and are now producing "new generation" versions of their products. The new versions are lighter, which contractors like. They claim they are more mold resistant because instead of using cellulose as a filler (as in Hardiebacker), they use what appears to be tiny styrofoam pellets. The current pure cement board products are to be phased out and replaced by the new generation products which are not tested or approved for hearths or NFPA wall shields.

Write the mfgs now if you want them to continue to sell pure cement board.

edit: update, USG stated that the little white pellets are perlite and non-combustible.

 

[Jags]

Yeah, the new products meet the codes for fire retarding walls, but not as hearth components. In the name of "improvements". Jeesh.

 

[begreen]

Contact info:

USG (Durock):
800.950.3839
[email protected].

Custom Building Products (Wonderboard):
13001 Seal Beach Blvd
Seal Beach, CA 90740
562-598-8808
800-272-8786 (customer support)
webform: http://www.custombuildingproducts.com/ContactUs.aspx?user=arc&lang=en

 

[wolfkiller]

FYI The tile backer sold for hearths is not enough of these companys sales for them to care. This is from my Durock rep. I buy about 10000 sheets of tile backer a year. The new products perform a lot better in wet aplications. It sucks for hearth building but there is not a lot we can do with our small buying power.

 

[begreen]

I can see how these products are better in wet locations than HardieBacker board, but how do the new products perform better in wet locations than the pure cement product?

I'm guessing that this is more a case of contractors liking the new product more due to lighter weight and easier cutting, which are Hardiebacker's strengths. It wouldn't surprise me if the new product is also cheaper to manufacture due to the fillers.

 

[ecfinn]

So should I buy some old durock now or is it already OOS? I'm going to be building a hearth this summer and was planning to use that since that's what I used on my hearth extension in my living room. Are there any other products rated for this type of installation if these two are gone?

Thanks,
Eric

 

[begreen]

The last time I checked it was still available at HD. After it's gone, it's gone. To my knowledge there are no other approved materials for tile. It would be good to get the NFPA discussing this. Kind of like digital TV. Nice for some applications but for rural locations you are sol.

 

[jlow]

I used micore r =1.1, my mechanical inspector only needed to verify that i used it and he approved my hearth pad. I did put fiberock to set the brick pavers.

 

[begreen]

Fibrerock is similar to hardibacker, it has cellulose added. If the stove's hearth requirements are not high and there is a layer of thick brick or stone on top, then this is less an issue.

 

[Mikeyvon]

I did a lot of soldering (my radiant heat system) using mapp gas on sawhorse table made of hardibacker. I could get it glowing red hot when heat applied, but it would only stay red with the heat and did not catch fire. I tried and tried to get it to catch fire and it would not happen. Once heat was removed, it would stop glowing red and cool, leaving very little scorching (black).

 

[Jags]

I did a lot of soldering (my radiant heat system) using mapp gas on sawhorse table made of hardibacker. I could get it glowing red hot when heat applied, but it would only stay red with the heat and did not catch fire. I tried and tried to get it to catch fire and it would not happen. Once heat was removed, it would stop glowing red and cool, leaving very little scorching (black).

Its not so much that it will catch fire, but outgas when heated. The cellulose filler used in the new stuff is basically styrofoam beads.

 

[oldgrezmonke]

I used micore r =1.1, my mechanical inspector only needed to verify that i used it and he approved my hearth pad. I did put fiberock to set the brick pavers.

I also used Micore . It was a little hard to find , you will have to go to a builder's supply rather than the D.I.Y. places like Lowe's or Home Depot . Its website can help you find a supplier near you , though it only lists places to which they sell direct and some of those only do wholesale , but they can probably lead you to a place that will sell to anyone .

 

[begreen]

Micore is not suitable for tile underlayment. Even with a layer of Micore, a top layer of cement board is required for a good tile job.