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clofgreen 10-27-2011 09:05 AM

Hardibacker as hearth leveler?
I've been doing some thinking about how to level the hearth so that bricks are level, especially over perlcrete insulation. The consencus seems to be using a layer of 50/50 sand/fireclay but I wonder if Hardibacker could be used. I've been doing some Internet searching, especially at | Wood Stoves, Fireplace, Pellet Stoves, Gas Stoves and More - Forums! and think that 1/4" hardibacker might be a good solution.

I have personally placed Hardibacker over a sustained high heat for five minutes and there was no damage to the board, no smoke, no fumes, just a very slight crack.

Has anyone tried Hardibacker under their floor? What are your thoughts?


mrchipster 10-27-2011 10:39 AM

Re: Hardibacker as hearth leveler?
The problem is really not the foundation but the variation in the thickness of most firebricks. I laid my floor out on a sheet of plywood for positioning and cutting and they were not level even on 3/4 inch sanded ply.

The sand/fire clay method is tried true and easy. Use a 1/4 inch notched trowel and a rubber hammer and it will go well. just like laying tile but easier.


clofgreen 10-27-2011 11:12 AM

Re: Hardibacker as hearth leveler?
Ah, good point. I was under the impression that the perlcrete and ceramic fiber board was causing the bricks to be uneven. The bricks I have are very uniform. But on another point, people use a 5:1 perlcrete mix to give the oven a solid base to sit on. If Hardibacker were used to distribute the weight, a much leaner mix could be used providing greater insulation values. I'm not trying to defend using Hardibacker, just trying to think through the issue.


GianniFocaccia 10-27-2011 02:03 PM

Re: Hardibacker as hearth leveler?
Hardibacker is not a refractory material. I called the James Hardie company at one point and they would not support the strength nor durability of their board in an environment nearing 500F. Floor bricks in direct contact with Hardibacker will exceed this temperature over many repetitive cycles.

Go with the sand and fireclay. Like Chip said: it's proven and easy, but also inexpensive.

clofgreen 10-27-2011 02:25 PM

Re: Hardibacker as hearth leveler?
Thanks Chip and John for your great comments.


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