Help with hearth extension repair

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AStein

New Member
Jan 14, 2022
5
15238
Help please,
I pulled up the marble surround and hearth extension and found a mess.
The base was/ is filled with bricks and mortar, all crumbling and .... a mess.
House was built in the 1980s, the fireplace is gas logs, husband doesn't want an insert :(
I want to somehow refill/ level the extension area off and put a slate slab down.
Any help on how to achieve this is most welcome and thank you.

IMG_1029.jpeg IMG_1030.jpeg IMG_1031.jpeg
 

EbS-P

Minister of Fire
Jan 19, 2019
2,675
SE North Carolina
I’d mix up some mortar mix making sure that what ever I put down was lower by a bit than I wanted for the piece of slate. The use thin set to set the slate.

Your friend has shared a link to a Home Depot product they think you would be interested in seeing.



 
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bholler

Chimney sweep
Staff member
Jan 14, 2014
28,696
central pa
Help please,
I pulled up the marble surround and hearth extension and found a mess.
The base was/ is filled with bricks and mortar, all crumbling and .... a mess.
House was built in the 1980s, the fireplace is gas logs, husband doesn't want an insert :(
I want to somehow refill/ level the extension area off and put a slate slab down.
Any help on how to achieve this is most welcome and thank you.

View attachment 289853 View attachment 289854 View attachment 289855
It needs to be a self supporting concrete slab with no combustibles touching the bottom of that slab. So you need to either make removable wood forms or metal ones. Then drill holes in the hearth slab at differing angles for rebar to tie the two slabs together
 

AStein

New Member
Jan 14, 2022
5
15238
I’d mix up some mortar mix making sure that what ever I put down was lower by a bit than I wanted for the piece of slate. The use thin set to set the slate.

Your friend has shared a link to a Home Depot product they think you would be interested in seeing.



So with the mortar mix, should I remove all of the random bricks or just add mortar around them?
 

AStein

New Member
Jan 14, 2022
5
15238
It needs to be a self supporting concrete slab with no combustibles touching the bottom of that slab. So you need to either make removable wood forms or metal ones. Then drill holes in the hearth slab at differing angles for rebar to tie the two slabs together
Yikes. This is seems well beyond my diy skills and well beyond what was here before...
My understanding from reading the building codes is the extension needs to be 4 inch deep of noncombustible....can there be wood under those 4 inches?
Also is the rebar needed.
I want to do this correctly, but also don't want it to be overkill.
Thank you in advance for your help.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
28,696
central pa
Yikes. This is seems well beyond my diy skills and well beyond what was here before...
My understanding from reading the building codes is the extension needs to be 4 inch deep of noncombustible....can there be wood under those 4 inches?
Also is the rebar needed.
I want to do this correctly, but also don't want it to be overkill.
Thank you in advance for your help.
Yes minimum 4" thick and no combustibles can be in contact with the bottom of the slab. Rebar is not nessecarily required but the slab needs to be self supporting so pretty much it is required
 

AStein

New Member
Jan 14, 2022
5
15238
Yes minimum 4" thick and no combustibles can be in contact with the bottom of the slab. Rebar is not nessecarily required but the slab needs to be self supporting so pretty much it is required
So this fireplace in on the main level with a basement below...maybe a silly question, but how do I make the slab self supporting within a ceiling
 
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bholler

Chimney sweep
Staff member
Jan 14, 2014
28,696
central pa
So this fireplace in on the main level with a basement below...maybe a silly question, but how do I make the slab self supporting within a ceiling
Take everything out from the top. Then make metal forms you attach to the framing. Then you drill holes at varying angles into the main hearth slab for rebar to tie them together. After that make a rebar grid and pour your slab. Many times the main hearth slab isn't any good either so you end up doing a whole new slab. Redoing these is a big pain in the ass and takes allot of time. I always allow 2 days for me to do them without a top finish.
 

AStein

New Member
Jan 14, 2022
5
15238
Take everything out from the top. Then make metal forms you attach to the framing. Then you drill holes at varying angles into the main hearth slab for rebar to tie them together. After that make a rebar grid and pour your slab. Many times the main hearth slab isn't any good either so you end up doing a whole new slab. Redoing these is a big pain in the ass and takes allot of time. I always allow 2 days for me to do them without a top finish.
Thank you for the response.
Ugh, Am I ever regretting taking out the marble that was there.
So what grade/ type of metal do you recommend?
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
28,696
central pa
Thank you for the response.
Ugh, Am I ever regretting taking out the marble that was there.
So what grade/ type of metal do you recommend?
In situations like yours I would typically weld up a support frame out of angle iron first then use 20 gauge.
 

jalmondale

Member
Dec 16, 2021
118
NY
What's currently under the bricks? If there's already a self supporting non-combustible slab, and you just need to essentially repair the top of it (crumbling bricks), I think it'll be way easier than if you're trying to redo the entire thing.

I'm also curious about whether non combustible insulation (mycore) might simplify any of this (I don't actually know, but maybe someone else does).
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
28,696
central pa
What's currently under the bricks? If there's already a self supporting non-combustible slab, and you just need to essentially repair the top of it (crumbling bricks), I think it'll be way easier than if you're trying to redo the entire thing.

I'm also curious about whether non combustible insulation (mycore) might simplify any of this (I don't actually know, but maybe someone else does).
I can see wood form in the front which almost always means there is wood under it as well. And no there is no allowance in code for insulation to change anything.