Hardie versus Durock in woodstove hearth

[Samandothers]

I am working on a hearth design. The R value needed is .40 . I plan to place a piece of Micore 300 over the subfloor and then cement board then tile. The cement board will help with R but is necessary for the tile install and to help protect the Micore. My question is which Durock cement board or Hardie. I see Durock mentioned a lot here. I don't seem much about Hardie. Is the Hardie a bad choice or does Durock properties that would give it the nod over Hardie.

Thanks for your help/thoughts on this.

 

[DAKSY]

Your call. HardieBacker 1/4" Cement Board is deemed noncombustible when tested to ASTM E 136 and can be used in conjunction with other noncombustible materials around a fireplace. Durock cement boards are more textured thus they are easier to apply. The texture allows the cement board to stick more firmly because of the friction between the adhesive and texture. HardieBacker cement boards also adhere firmly but lesser than Durock cement boards because they have a smooth surface.

 

[Samandothers]

Your call. HardieBacker 1/4" Cement Board is deemed noncombustible when tested to ASTM E 136 and can be used in conjunction with other noncombustible materials around a fireplace. Durock cement boards are more textured thus they are easier to apply. The texture allows the cement board to stick more firmly because of the friction between the adhesive and texture. HardieBacker cement boards also adhere firmly but lesser than Durock cement boards because they have a smooth surface.

USG site indicates: "USG Durock® Brand Cement Board with EdgeGuard panels should not be used in areas where they are exposed to temperatures that exceed 200°F (93°C). "

This may be the limit of the ASTM E 136, not sure, and thus the reason for this. I have not yet seen Hardie's disclaimers still looking and reading.

 

[sesmith]

Durock specs say it has an r value of .39 per half inch. I've never found r value specs for Hardie backer when I've looked.

 

[Highbeam]

I’ve used both for tile jobs and much prefer the hardie. It’s just cleaner.

 

[Samandothers]

I have found something on Hardie in an older legacy report but it does not make a lot of sense. R values in the table don't increase in all cases with the thickness of the board. I may try to call Hardie to see if I can get some info.

I called USG about Durock and they basically stated it was not tested for this type use or only tested to 200 degrees.

I am leaning to Hardie as it appears the compressive strength is greater. You can see that in the screenshot from Hardie Backer Cement Board guide, if I am reading it right. With Micore below this layer of concrete board I should be ok on R value for protection of subfloor and trusses without the Hardie contributing.

You would think manufactures would make this easier to gain understanding how they product may help . Why is this such a difficult thing that everyone seems to struggle with. I guess it give the manufacturer and out should there be an issue. Sorry a bit of a rant there.

 

[Dustin]

my hearth didn’t actually need any R value, just ember protection.

That said, I used hardie for the entire project. I ran out toward the end and needed a small piece and could only get durrock.

point being, I found hardie to be more rigid than durrock, cleaner, and easier to work with

 

[Samandothers]

Thanks for the replies. Today I talked with the guy that will do the tile work in the house. I shared I had the Micore and wanted to use a cement board over it to help support the tile and spread the stove load. He indicated he has used both Hardie and Durock and can source both. Ironically he indicated he liked the Durock. I asked if he would do the hearth prior to installing the tile since he's done this before. He indicated he would. This greatly simplifies the process and I may go that route since the location of the house is 3 hours away.

 

[begreen]

Personally I'd skip the micore and put down 2 layers of 1/2" Durock in alternate directions so that no seams overlap. That will provide R=.78 hearth protection.

 

[Samandothers]

Personally I'd skip the micore and put down 2 layers of 1/2" Durock in alternate directions so that no seams overlap. That will provide R=.78 hearth protection.

Interesting
I have the Micore ordered and on its way. I am curious, why would you do this versus the Micore and Durock to get 1.4 ish of R?

 

[begreen]

Interesting
I have the Micore ordered and on its way. I am curious, why would you do this versus the Micore and Durock to get 1.4 ish of R?

Looks like there may be a typo in your original posting. It says "The R value needed is .40". R=1.40 would take 4 layers.

 

[Samandothers]

I do only need an R value of .4 and am in over kill area with the Micore and a cement board. Two layers of cement board would exceed the .4 R needed. I understand your point. Thank you