replacing old hearth and surround, questions about materials for hearth

[krisl123]

Hello
I'm new here, currently remodeling a fireplace hearth and surround, the house was built in 1969 its a tri level and the fireplace is on the lower level with a concrete floor. I'm trying to figure out the proper way to rebuild the hearth, the firebox is elevated about 14" off the floor, when we tore out the old hearth it was topped with flagstone, the surround was all old natural stone the hearth was created out of cinderblocks as the base.
I plan on using flagstone again as the hearth and below that as well as around the firebox will be manufactured stackstone. The stack stone cab be installed using cement board and polymer modified mortar which I plan to do. Can the hearth be built with 2x4 covered in plywood then cement board then the flagstone? Trying to achieve the non combustible materials status for the hearth, any advice or guidance would be greatly appreciated. I've attached a photo

 

[Sodbuster]

Why not just use cinder blocks again, they're not hard to work with, and since your work will be covered up, they don't need to be pretty. Would eliminate any noncombustible issues, and would be really rigid. Welcome to the forum!

 

[krisl123]

my total height from floor to bottom of the firebox is actually 15 1/4", since I'm not totally familiar with using cinder blocks I'm not entirely sure how easy or difficult it would be to achieve my desired height of 13 1/4" allowing 2" for flagstone

 

[bholler]

Can the hearth be built with 2x4 covered in plywood then cement board then the flagstone? Trying to achieve the non combustible materials status for the hearth, any advice or guidance would be greatly appreciated. I've attached a photo

No it needs to be made completely of noncombustible materials. here is a copy of the code you need to follow
http://www.rumford.com/code/clearances.html

 

[Sodbuster]

Go to your local home center and look at all the different size blocks they carry. You can make almost any dimension you need, don't forget about the mortar, it can make up some fudge factor. Do you want the flagstone to be flush with the firebrick or slightly above it? I assume this is going to be a natural fireplace, correct?

 

[Sodbuster]

I guess some people don't want to hear a real answer, they want confirmation of what they have planned in their head. To each his own.

 

[begreen]

8" full block + 4" half block + a couple layers of 1/2" Durock will get you close.