Replacement hearth

[MikeStaten]

When tearing out my old hearth I noticed that the wood underneath was charred. I am planning on doing the following and was hoping that others could chime in on whether this will work or not.

A little background.. The fireplace is on the first floor on an exterior wall. Chimney and firebox are essentially outside/through the exterior wall and hearth starts at inside of exterior wall and goes into living room. My basement is unfinished so easy access to ceiling and floor of hearth. I plan on putting a wood burning insert in when I'm done. Leaning towards a jotul 450 kennebec but open to ideas.

Anyway, to rebuild the hearth I was planning on laminating 1/2 durock as the bottom layer, 3 sheets of micore 300, one 18 gauge stainless steel sheet metal and then another sheet of durock over that. I think what I've mentioned so far is probably overkill but I'm ok with that. My existing firebox has firebrick in there as a base but I'm not sure what's underneath that but it would be outside of the house so should not matter?? However, just in case, Can I extend this new hearth (durock, stainless, micore) material right over the existing firebrick within the fireplace itself so that I have a smooth continuous surface from front of hearth to the back of the fireplace? I then plan to add a 1.5" bluestone hearth outside of the firebox and then fill in the inside of the fireplace with additional layers of durock and refractory mortar until the inside floor of the fireplace is level with the bluestone hearth outside of the fireplace. This is just my initial idea so very open to suggestions on improvements. Sorry if my terms are unclear, not that familiar with fireplaces. My main goal is to have a safe fireplace that will be suitable for a wood insert.

Thanks,
Mike

 

[begreen]

Yes, that's overkill. 1" of micore will more than suffice. I think I would prefer one less layer of micore and 2 layers of durock on top for added rigidity. Micore is quite soft.

 

[MikeStaten]

Thanks. However, That insert requires almost r3 for the floor. Do you think it's ok to have bare durock under the stove in the firebox or better to cover it will mortar? I'll need to mortar all of the seams anyway. Plus the durock within the fireplace may not be the same level as the durock under the hearth so covering with mortar may be the easiest way to level it off.

 

[bholler]

Just cut the framing out make a form out of sheet metal and pour a hearth extension the way it should have been done to start with. Just make sure you anchor it to the hearth floor well with pins

 

[begreen]

Thanks. However, That insert requires almost r3 for the floor. Do you think it's ok to have bare durock under the stove in the firebox or better to cover it will mortar? I'll need to mortar all of the seams anyway. Plus the durock within the fireplace may not be the same level as the durock under the hearth so covering with mortar may be the easiest way to level it off.

The C450 requires R=2.92 for the hearth insulation, 3 layers of of 1/2" Durock will give you R=1.17, 1" of Micore 300 will provide an additional 2.22 r value for a total of R=3.39.

 

[MikeStaten]

Perfect. Thank you for your responses.