Hardie Board Woes

Did you pick up hardie Board?= Siding
or hardie brand of Durarock Tile backer

You should be looking for Dura rock

Take it back - you want the heavier stuff with the fibers exposed - don't worry about them.

Sounds like Kenny bought 3'x5' sheets of Hardie Backer. Not the best option for a hearth. lotta organics and cellulose in there, prone to emitting nasties when heated.

Dunno what you're planning to put over it, so dunno what - if any - R-value requirements you're trying to comply with. Might be you're ok with it.

Might be you wanna go find some Durock or Wonderboard to use. Homers sells all 3, typically. I'm a fan of the Durock, but not the Durock-NEXT, which is similarly "fortified" with similar cellulose-type materials. I used Wonderboard in my hearth build, and found it quite acceptable. It does get crumbly, but you can manage that. sweep it all up, use a good thinset (i.e. Versabond) and you'll be all good

I went with 1/2 inch Durock (old stuff) which will actually have a sticker/label on it saying it is listed and approved for hearth construction . . . or something to that effect. About three weeks ago the Inspector and I went on a "field trip" to Home Depot to see if they were still selling the old stuff or only the new stuff . . . the good news is that they were still selling the old stuff.

Smokey Foot said:

I used wonderboard also on my hearth as all I could find was the new Durock.

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And of course, not to bring up the Oslo hearth requirements again (do you think Jotul would be surprised if they read this forum?), you should be fine as your tile provides the ember protection with no r-value needed

Just finished adding 1/4" Hardi board and 3/8 slate under the new Mansfield. Please tell me you're not suggesting I move that stove again! I only used it to raise the stove 3/4", not for R value. I called James Hardie 800 number in the store and they told me it would transfer heat, but not burn...

Whatcha got under the 1/4" Hardie, Russ?

And they're right - it won't burn. it'll outgas and degrade.

The Mansfield is sitting in the middle of a double sided masonry fireplace, so under the slate and hardi backer is a layer of firebrick and more masonry under that. Not too interested in a slow, steady off gas

ah yes - you have that cool 2-sided fp. got the mansfield, didja? cool. stuck it over Hardie, huh? hmm...

well hottest spots are actually out front of the door. it's actually comparably quite cool directly under the stove. so might be your best bet is to replace it out front without moving it. or just leave it and see what happens.

You should go to your local lumber yard. They will have a good DuraRock (with out the styrafoam beads). It is heavy, but is what it is.... cement and a little fiberglass.