Fireplace firebox cement/concrete?

[Jorj]

In my fireplace firebox, behind the lintel in the 'throat' on the front side, there is a coating of concrete or cement over the bricks that is relatively smooth so the draft will flow easily up past the damper.

One half of this concrete/cement has broken out over the years. I have removed all of the loose concrete and want to patch it. Does anyone know what material would work well and hold up to the heat in the firebox? I tired some clay like material that someone sold me and it dried up, cracked and most of it fell out because it contracted so much. It ended up looking like a salt flat that cracks after a heavy rain.

Any ideas on what type of concrete or cement to use to make this repair in the firebox??

 

[chopnhack]

Does anyone know what material would work well and hold up to the heat in the firebox?
Any ideas on what type of concrete or cement to use to make this repair in the firebox??

Hi Jorj, you are looking for refractory cement. That is what is used to make fireboxes and some folks use it to make forges. The key is the drying period after you place the cement. You need to moist cure it for a few days and then allow it to dry for a week or two on its own. Then start with small, short fires to help drive out any remaining moisture without cracking the cement. After its completely dry, you should have no further issues, unless there is some movement/settling causing the cracks in the first place.

 

[Jorj]

Chopnhack,

Thanks so much. That sounds right on. Have to get the soot off the old brick before I apply the refractory cement. Will probably use a 4" grinder with an abrasive brush to clean the brick and remaining solid cement.

Jorj

 

[chopnhack]

Awesome, good luck and don't rush the cure cycle!