Hearth pad extension questions

[faultymechanics]

To be proper, the hearth floor in the fireplace and the hearth extension, should be one continuous cement base that is reinforced with metal (rebar or mesh).

Thread 'help with rebuilding hearth'

Jan 25, 2023

We recently purchased a 1925 home in Philadelphia, and we're having a wood-burning insert professionally installed in early March (it was the earliest they could get to us). However, I've needed to do some demolition of the old mantle (a super ugly 2x4, drywall, and mirror monstrosity) and hearth to get it ready for the installers. We have a 2" piece of slate countertop we're going to use for the hearth extension, but the more I dug into the work around the hearth--literally and metaphorically--the more questions I had.

The hearth extension doesn't seem to be connected to the hearth...

• A Stove in Philly
• Replies: 10
• Forum: The Hearth Room - Wood Stoves and Fireplaces

Post in thread 'Hearth extension is not supported nor attached?'

Jul 31, 2023

Cement board to close fireplace, 3/4" plywood for hearth extension, level frame around extension, will use that as a guide.



...22 bags of sacrete 6000psi 25kg/bag later:


We had 2 wheelbarrows, mixing in one while another being unloaded.

Learn from our mistakes: down't mix 2 bags at a time, it takes too much effort to do this. It's easier and faster to mix one bag in a wheelbarrow.
Used a steel angle with a level to scrape and level the surface.
For compacting, we used bosh drill hammer set into hammer only mode, and 2x4 flat attached to a bit. When compacting...

• TomasB

• 

Oh the actual base of the hearth is one giant cement pour, from 1930 so we dont know if there is rebar.

Im just adding more thermal protection to the existing hearth extension (but i need to demo the old tile first to fit in the new micore, durock and tile.

 

[begreen]

Is the current hearth extension deep enough to meet the new requirements? Is it all cement underneath (no wood form supporting it)?

 

[faultymechanics]

Is the current hearth extension deep enough?

Won't know until I demo the old one. Im guessing it will be about 1" higher than the current setup. I plan to use durock under the insert to level that out with the newly increased height of the extension.

Just saw your edit, current hearth extension has the form still under it and we're unsure due to the age if its structural(no clue if theres rebar inside) which is why I'm beefing up the extension.

 

[begreen]

The form should have been removed. It is not allowed to be under the fireplace by code.

 

[faultymechanics]

The form should have been removed. It is not allowed to be under the fireplace by code.

It only remains under the extension, which is why I'm going through all this trouble. No idea why they left it back in the 30s.

The actual fireplace where the insert sits is concrete over dirt.

 

[faultymechanics]

Should I put down a layer of self leveling compound before the micore?

Additionally, if I wanted to use a slab of stone vs tiling, do I still need the Durock layer over the micore?

 

[begreen]

The micore should go down on a leveled and flat surface. I don't know about the thick stone. One definitely doesn't want to dent the micore. Some layer of protection seems worthy, but I am not a stone mason.

 

[faultymechanics]

Things have gotten interesting. It would appear the previous tile was not on cement board but tiles right to the cement hearth.

What's the easiest way to get q flat surface? Mortar coating and then lay cement board over it? Then two layers of micore and another layer of durock cement board?

Do I mix up some cement and level it out with the wood floors that way?

I plan to go out another few inches but since the R value will be high enough, I'm not planning to cut away more of the wood floors, just lay the new hearth extension(probably about 3") on top of the floor.

 

[faultymechanics]

Current plan:

Fill cracks, use floor leveling compound to make even with current wood floor. Use 3/4" plywood over top and extend extension from 19" to approximately 22"(may be more if it makes tiling easier). Screw plywood into masonry hearth.

Layer 1" of micore and 1/2" of durock on top of plywood, screw into plywood.
Tile with 1/2" square notched trowel and 1/4" tile. Should result in a 2.75" raised hearth extension.

Will be using 2.5" fire brick to raise stove to level of hearth extension, least that's what my sweep suggested. (Fireplace hearth its about 1/4" above wood floor level so 2.5" should get it even with new extension).

 

[faultymechanics]

Tiling is up next. Did I use enough screws? Haha. Hopefully those arent going to be transferring any substantial heat to the plywood below.