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So I've built a metal frame that is going to be used as my outdoor bbq. I am ready to install siding on it and I was told to use HardiBacker.

I googled it and apparently it isn't for use outdoors. What is a good cement board or other material that I can use as the sidings for my bbq?

It is on the edge of a patio and lawn so the sprinklers WILL get it wet about every other day. I am open to other suggestions

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I am really surprised by that. I have used HB a ton of times... Left this stuff outside in a bucket of water. 10 mins later dry as a bone. Really wonder the reasoning behind it but I see it on their fact sheet. (I would still use it) –  DMoore Aug 1 '13 at 6:26
    
What is the intended end finish for the sides? Tile? Stucco? –  SpectralGhost Aug 1 '13 at 14:42
    
The sides are going to be stone veneer (the fake kind). I think I am going to stick with the HB. On their FAQ it says In accordance with National Evaluation Service Report NER-405, HardieBacker board is recognized only as an interior substrate. It doesn't necessarily say no. My dads outdoor BBQ is made with HB, although his is stucco'd –  Ronnie Aug 1 '13 at 18:27
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2 Answers 2

Edited to remove ANY subjectivity:

HardieBacker is made from wood (cellulose fibers) and cement and carries a limited warranty for exterior use and only in certain climate zones. See HardieBacker's 10-Year Limited Warranty for Exterior Use

Durock is made from cement and fiberglass mesh. Wonderboard and others are made similar to Durock.

Subjectivity Here:

Obviously, there is a reason for the substantial difference in warranty between interior and exterior applications. My belief is that the cellulose will eventually break down from the shifting between warm humidity/ and freezing temperatures, especially in applications that would limit the ability for the product to appropriately air out. Durock is cement and fiberglass, and while both products will react to hot/cold like poured concrete, I would prefer the product that does not use wood. Given that they cost about the same, I would rather use something that the manufacturer expects to be able to withstand the 10-year warranty, over one that doesn't expect it to in nearly half the U.S.

But again, that is my subjective opinion.

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When does it break down? I have a couple of pieces in my shed awning that get wet sometimes. They have been there for 7-8 years (too lazy to walk them to the trash and might use them). They look brand new. I would assume if used for a grill they would be completely covered with rock/tile/grout/stucc/whatever. –  DMoore Aug 2 '13 at 18:45
    
will be covered in stone veneer –  Ronnie Aug 2 '13 at 19:02
    
@DMoore -- updated my answer. –  Jacob S Aug 2 '13 at 19:23
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I would use Durock, a concrete board product of USG (United States Gypsum Company). It is very durable and works for exterior or interior applications. Here is the installation guide, and more information on their 10 year warranty for exterior installations.

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I have tested Durock side by side with HB. It is affected by moisture way more than HB. Really bugging me now why HB can't be outside. Maybe they are saying that so you buy their siding. –  DMoore Aug 1 '13 at 6:34
    
I think for code compliance you cannot use it outside. It probably doesn't block the minimum amount of moisture, but I bet it would be fine. What if I paint the HB with a water sealant? I'm in southern cali so it doesn't rain all that much. I'm more concerned about my sprinklers –  Ronnie Aug 1 '13 at 18:43
    
Given that you use it in shower stalls, I'd think that it would be fine as long as the surface material applied to it is waterproof. You are not going to use it unfinished as an outdoor sheet-rock but as the substrate for stone veneer. Make sure the mortar isn't porous and you should be ok. –  Fiasco Labs Aug 1 '13 at 20:29
    
Well, I'll be using this: airstone.com and it says no mortar required. It simply gets "glued" on with some special adhesive which is why I was wondering about a water sealant directly on the HB. In use for my application: airstone.com/nice-work-charlie –  Ronnie Aug 1 '13 at 20:35
    
@FiascoLabs sorry, forgot to tag you –  Ronnie Aug 1 '13 at 21:35
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