Hearth extension is not supported nor attached?

[TomasB]

I have one of those cases, where the hearth extension is separating from the fireplace, by about 5mm or 1/4"



I can't see any rebar in the gap, just some loose cement crumbles.



The depth of extension from top is 21":



Looking from the bottom, it seems it sits on 2" ledge on fireplace, while the other end was just lodged against a joist?


This kinda made me quite nervous, and I added 2x4, glued crap out of it using PL Premium, added a thick bead of glue on top just to spread the load as well, and set in place using 1/4"x3" screws. Oh, before that I lifted the slab just slightly, by 3mm or so:


Question #1: I have no idea how it didn't go down before. Is it because it was simply lodged between fireplace and joist on angle?

I understand that this 2x4 technically is not to code, because hearth extension suppose to stay in place on its own attached to fireplace, but I consider this way better compared to what it used to be. We used to use the fireplace like that, and it was touching joist anyway.
Oh, and after lifting the hearth extension, now I can squeeze a metal cutting blade between the extension and the joist.

Going forward, the plan is to install a wood burning insert inside the fireplace (as opposed to on top of the hearth extension), bring the hearth extension height close to hearth level, and finish with granite slab.

Since we'll put on top more weight, I feel like there is a need to attach a hearth extension to the fireplace, and this is what I have in my mind, and would like to check with people who understand way more than me.

1. Drill horizontal holes into fireplace cement bricks at the ground level, 4" deep, drill vertical holes into the existing hearth extension slab, around 2-3" deep, and use "L" shape rebar to hook hearth extension. Then using epoxy or post setting cement to secure those rebars in place.
2. After that, prime existing hearth extension, and pour over concrete at 2.5-3" thick.
3. At this point, I think it should be quite a significant improvement over what it is right now, and I'd raise the hearth extension to the fireplace level using hollow concrete blocks spaced apart by 6" (all this to minimize weight), and cover all that with Hardie (cement) board from top and sides, screw in using tapcon screws - this would be the surface to attach granit slab to.
4. After that, repoint and improve the state of the fireplace brick work.



Let the poking at this plan begin, I appreciate everyone's input.

 

[Ashful]

Any chance to just cut the whole mess out and start over? Hearth extensions like this are often corbelled into the foundation of the fireplace, in cases where the foundation does not extend under them. This could be done without enormous effort, depending on the material and make-up of the fireplace foundation.

In many older houses (18th century), the hearth extension is framed out like yours, but I believe that today all hearth extensions must be entirely constructed of non-combustible materials.

 

[TomasB]

Hearth extensions like this are often corbelled into the foundation of the fireplace, in cases where the foundation does not extend under them. This could be done without enormous effort, depending on the material and make-up of the fireplace foundation.

The house is from 1950'ies, Canada, British Columbia. It would have been easier to just level the house and rebuild, it has/had so many screw-ups, every task/project takes so much more effort compared to what it would be to start from scratch.

Any chance to just cut the whole mess out and start over?

The upstairs, where the fireplace is located, is being renovated, and we live in the "not really finished" basement, so removing an existing hearth extension is not really an option.

I believe that today all hearth extensions must be entirely constructed of non-combustible materials.

Apart from that 2x4 I attached, I will not use combustible materials for hearth extension, so I'm pretty much covered there?

BTW, I updated the post with a drawing of the plan.

 

[Ashful]

Apart from that 2x4 I attached, I will not use combustible materials for hearth extension, so I'm pretty much covered there?

Paging @bholler.

 

[bholler]

The house is from 1950'ies, Canada, British Columbia. It would have been easier to just level the house and rebuild, it has/had so many screw-ups, every task/project takes so much more effort compared to what it would be to start from scratch.


The upstairs, where the fireplace is located, is being renovated, and we live in the "not really finished" basement, so removing an existing hearth extension is not really an option.


Apart from that 2x4 I attached, I will not use combustible materials for hearth extension, so I'm pretty much covered there?

BTW, I updated the post with a drawing of the plan.

The right way to do it is remove the existing slab make a metal pan under it drill rebar into the existing hearth pad at alternating angles and then pour a new extension pad.

 

[gthomas785]

Why not just support it with something non-combustible like a steel angle iron?

 

[Ctwoodtick]

Why not just support it with something non-combustible like a steel angle iron?

I think the main issue is that it’s a faulty set up, even with a steel angle iron.

 

[gthomas785]

I think the main issue is that it’s a faulty set up, even with a steel angle iron.

The OP said removing the hearth extension is not an option so I was just suggesting a way to add the desired support without creating an additional code violation.

 

[TomasB]

The right way to do it is remove the existing slab make a metal pan under it drill rebar into the existing hearth pad at alternating angles and then pour a new extension pad.

In which case, I don't see anything wrong of what I'm doing: consider an existing pad is your suggested "metal pan".

I thought about drilling holes into fireplace at angle too, like 30 degrees or so downwards:
- it would allow making those holes deeper
- should improve holding power.

A new concrete pad poured on top is like a rebuilt new pad. I think I am going to drill some vertical holes into existing hearth extension and screw some tapcon screws, leave them sticking out, to introduce mechanical bond between new pad and old one. But will see how it goes after I put those rebars

If you excuse me now, I'm going to drill some holes.

You mentioned "existing pad". If I understand you correctly, there is no pad in the hearth.

This is a picture of the hearth (I removed a couple fire bricks since they were loose anyway):


And here is a scary part at least for me, underneath of hearth pad, the picture taken through ash cleanup:


Question: will it be able to support a fireplace insert, considering that the rebar is all rusted out already?

If not, how this should be addressed, if possible, without too much intervention, ie rebuilding a whole thing.

 

[bholler]

In which case, I don't see anything wrong of what I'm doing: consider an existing pad is your suggested "metal pan".

I thought about drilling holes into fireplace at angle too, like 30 degrees or so downwards:
- it would allow making those holes deeper
- should improve holding power.

A new concrete pad poured on top is like a rebuilt new pad. I think I am going to drill some vertical holes into existing hearth extension and screw some tapcon screws, leave them sticking out, to introduce mechanical bond between new pad and old one. But will see how it goes after I put those rebars

If you excuse me now, I'm going to drill some holes.

You mentioned "existing pad". If I understand you correctly, there is no pad in the hearth.

This is a picture of the hearth (I removed a couple fire bricks since they were loose anyway):
View attachment 313485

And here is a scary part at least for me, underneath of hearth pad, the picture taken through ash cleanup:View attachment 313486

Question: will it be able to support a fireplace insert, considering that the rebar is all rusted out already?

If not, how this should be addressed, if possible, without too much intervention, ie rebuilding a whole thing.

Ok so you don't have a hearth slab at all and an unsupported hearth extension slab. Honestly I would take out the hearth floor and hearth extension and pour a new slab for both like it should have been to start with. The only other option I see is open up the ash dump, drill for rebar and build forms under your current hearth floor and pour through the ash dump. Then redo the hearth extension properly

 

[TomasB]

Ok so you don't have a hearth slab at all and an unsupported hearth extension slab. Honestly I would take out the hearth floor and hearth extension and pour a new slab for both like it should have been to start with. The only other option I see is open up the ash dump, drill for rebar and build forms under your current hearth floor and pour through the ash dump. Then redo the hearth extension properly

Thanks a lot for your input.
I was afraid you are going to suggest that.

In order to pour the proper hearth slab with extension (I think I see a way I could close the basement from underneath with plywood), does it mean I would need to gut the whole hearth? All those firebricks?
The issue I can see there is that the damper is sitting on the edges of the hearth. As well, the row of bricks that sit on top of damper are moving/loose! Initially, I was just planning to repoint them. Uhh!



It's quickly becoming too big job for me to handle.

 

[bholler]

Thanks a lot for your input.
I was afraid you are going to suggest that.

In order to pour the proper hearth slab with extension (I think I see a way I could close the basement from underneath with plywood), does it mean I would need to gut the whole hearth? All those firebricks?
The issue I can see there is that the damper is sitting on the edges of the hearth. As well, the row of bricks that sit on top of damper are moving/loose! Initially, I was just planning to repoint them. Uhh!

View attachment 313487

It's quickly becoming too big job for me to handle.

The plywood would need to be removed after the pour.

And yes the entire firebox and damper probably need to come out as well which is why I suggested opening up the ash dump and pouring a slab under that current floor

 

[TomasB]

The plywood would need to be removed after the pour.

The plywood is just for the demolition, to protect debris going downstairs.

 

[bholler]

The plywood is just for the demolition, to protect debris going downstairs.

Ahhh ok

 

[TomasB]

And yes the entire firebox and damper probably need to come out as well which is why I suggested opening up the ash dump and pouring a slab under that current floor

Building a form that size without proper access, through a tiny hole?
Because I can only see removing a couple rows of bricks from the current floor.
The rest would need to stay to support the hearth, correct?

 

[bholler]

Building a form that size without proper access, through a tiny hole?
Because I can only see removing a couple rows of bricks from the current floor.
The rest would need to stay to support the hearth, correct?

View attachment 313488

You would open up the wall of the ash pit and build the form from underneath not through the ash dump hole

 

[TomasB]

You would open up the wall of the ash pit and build the form from underneath not through the ash dump hole

Ouch! Thanks a lot!

 

[bholler]

Ouch! Thanks a lot!

It really isn't that big of a deal I open up ash pits 4 or 5 times a year. It's typically about 30 mins to open it up and about the same to close things up afterwards

 

[TomasB]

It really isn't that big of a deal I open up ash pits 4 or 5 times a year. It's typically about 30 mins to open it up and about the same to close things up afterwards

I would give the job to you on the spot. Planning visiting British Columbia, Canada any time soon? LOL

 

[bholler]

I would give the job to you on the spot. Planning visiting British Columbia, Canada any time soon? LOL

Lol nope

 

[TomasB]

Things are just falling apart without using any tools! I removed loose bricks by hand, I thought I will check what is the status of the rebar that suppose to hold hearth base, and it just fall out!


So, basically, the hearth is sitting on bricks that are not being held by any metal underneath.
I talked to a local mason, he suggested removing the hearth carefully, without causing a major collapse, which I'm doing right now brick by brick.


The plan is to build a proper slab once we remove what's possible to remove, and rebuild the hearth to fit a fireplace insert that we are yet to pick..

If you know a fireplace box/insert with a big window, please do chime.
At the moment, I'm thinking about Stuv 6-in or maybe Stuv 16-in: https://stuvamerica.com/en/products?scrollTo=wood-fireplaces-and-inserts

 

[TomMcDonald]

I would personally brick that thing up and move on. Not very helpful for your situation but geez, that looks like a major undertaking.

 

[TomasB]

I would personally brick that thing up and move on. Not very helpful for your situation but geez, that looks like a major undertaking.

Ha! I guess we have strong primal in us.. We like real wood fire.

At the same time, we are doing things that not many regular DIYers would be able to handle.

For instance, we have moved a beam into the attic, needing to cut into truss heals. I had to go through different engineers to get all the required specs - one for the beam, another for modifying trusses. That was quite a bit of fun, but the end of the result is awesome - no more beam glossing my hair as I cross to a sun-room. I consider that as a tax for being taller than the average.



Another one: installing hydronic heating across whole house:


So, yeah... I don't give up easy once I set my mind onto something.

 

[bholler]

Things are just falling apart without using any tools! I removed loose bricks by hand, I thought I will check what is the status of the rebar that suppose to hold hearth base, and it just fall out!

View attachment 313495
So, basically, the hearth is sitting on bricks that are not being held by any metal underneath.
I talked to a local mason, he suggested removing the hearth carefully, without causing a major collapse, which I'm doing right now brick by brick.
View attachment 313496

The plan is to build a proper slab once we remove what's possible to remove, and rebuild the hearth to fit a fireplace insert that we are yet to pick..

If you know a fireplace box/insert with a big window, please do chime.
At the moment, I'm thinking about Stuv 6-in or maybe Stuv 16-in: https://stuvamerica.com/en/products?scrollTo=wood-fireplaces-and-inserts

If you can do that without a collapse great. But good luck

 

[Ashful]

While the houses I generally work on are ~200 years older than yours, I've gotten myself into many similar projects, where the focus on rebuilding is so strong you can sometimes forget to step back and consider whether something different would have been better all along. The old "seeing the forrest from the trees" scenario.

If an insert in a fireplace really is your end goal, then carry on. But you might also consider this an opportunity to just blow this whole thing up and go to a freestanding stove in front of a brick wall. It would certainly perform better, give you more options, give you back more space, and might even look better.