HELP ! - Hearth build

[Vigil Igne]

Last minute and need input. Building hearth and not sure after seeing a previous post. Quadra fire Explorer III going on top and needs a Class I I hearth.

CONSTRUCTION: 2x6 frame, 3/4" plywood, 1/2" Micore 300, 1/2" Hardibacker, "Natural Stone and Large Format Tile" mortar (sold by HD), 12"x24" slate tile.

QUESTIONS:
1 - Hardie backer OK to use?
2 - is that mortar OK or do I have to use a non modified thinset?

 

[mol1jb]

Perhaps you could define Class II hearth so we understand the requirements.

 

[Vigil Igne]

From the install manual:

"FLOOR PROTECTION: Floor protector must be non-combustible material, extending beneath heater and to the front, sides and rear as indicated. The floor must be non-combustible or otherwise adequately protected from radiant heat given off by the unit and from sparks and falling embers. A layer of thin brick or ceramic tile over a combustible floor is not sufficient.
It is necessary to install a Type II floor protector of a minimum of 3/8 inch (9.5mm) thick metal clad millboard or equivalent with a minimum R value of 1.06, a minimum of 16 inches (406mm) in front of glass, and 8 inches (203mm) to both sides of the fuel loading door. Open the door and measure 8 inches (203mm) from the side edge of the opening in the face of the appliance.

I know I'm OK with the R value and clearances.

 

[begreen]

An alternative is to use higher R value Durock which is R=.39 for 1/2". 3 layers will easily exceed the required hearth R-value. Use of latex modified thinset is fine and recommended.

 

[mol1jb]

The last 2 tile jobs I have used Hardibacker over Durock as a personal preference, including my current hearth and stove install which I also used slate tile.

 

[begreen]

It will work when ember protection only is needed, though not my preference. Hardibacker is R=.26 vs Durock NexGen at R=.39.

 

[Vigil Igne]

Already have the Hardibacker so will just go with that. Good to know I can use the latex modified thinset! THANKS!