Cement for gap between firebox and hearth (picture)

[Tocramed]

Is there a certain cement/mortar that should be used to fill a gap between the firebox and the hearth? We have an insert installed, so there are no coals that will (hopefully) be in contact with this cement.

 

[bholler]

Well the right way to fix it is to tear it all out and replace it with a new hearth extension slab that is properly supported and tied into the hearth itself. But at the very least you need to support the hearth extension so it does not open up any more then confirm that the crack does not go down to combustible materials. At that point you can then fill the gap with regular mortar.

 

[Tocramed]

Hmm...it is hard to say why this ever moved in the first place. Clearly at some point it did and was filled in. It was like this when we bought the house, but we didn't notice until we pulled the old insert forward. Apparently this wasn't a concern during the chimney inspection and never got mentioned.

As far as I can tell, it is supported and the floor is a concrete slab on grade. So, if it is moving, I got bigger problems.

Once the Grizzly is out, I will clear the gap and see what it looks like. Thanks again for your help. Our new BK Princess in on the way.

 

[bholler]

As far as I can tell, it is supported and the floor is a concrete slab on grade.

If that is true then it is not a concern as far as chimney safety goes But it is a bit concerning otherwise

 

[Highbeam]

Meh, could have just been sloppy work when building the chimney/hearth in the first place. No need to worry about why it's there.

Fill it in with the same grout/mortar you used between the rocks on the wall. Matching whatever other material was used to fill joints in the hearth system for looks. Clean it out first, pick out loose junk first.

 

[bholler]

Meh, could have just been sloppy work when building the chimney/hearth in the first place. No need to worry about why it's there.

I agree if it is on slab it is not an issue but that very obviously moved and if it is on slab that could indicate a more major problem

 

[Tocramed]

The house was built in 1969 on a hill. There was an addition that did settle a bit, but that is supported by piers driven down to bed rock. No other signs of settling other than some cracks in the garage floor (about 15ft to the left of the fireplace), but they are hairline cracks. This doesn't mean much, but I am guessing this was a poor install of the heart extension.

I will clean it out, fill it, and hope for the best. If it ever opens up again, I will be calling a mason and/or foundation specialist. That would suck...the insert, liner, insulation, etc is already enough money. But hopefully it will be warm and it means I get to cut wood!

 

[Tocramed]

Thanks again guys!

 

[bholler]

I will clean it out, fill it, and hope for the best. If it ever opens up again, I will be calling a mason and/or foundation specialist.

That sounds like a good plan to me

 

[mrdinks]

My house had the same gap, I assumed it was an expansion slot and it was covered by the doors.
I would just mortar as others have stated.

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[bholler]

My house had the same gap, I assumed it was an expansion slot and it was covered by the doors.
I would just mortar as others have stated.

unless your house is on slab like his that gap can be potentially pretty dangerous. And it should not be there. the slab of the hearth extension should have been poured at the same time as the slab of the hearth with reinforcement in it.

 

[mrdinks]

Oh I agree if it actually moved that much then something is wrong.

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