Perlite & Cement Mix Has Some Give

Mattone Barile & Mattone Barile Grande Ovens
1

I filled the void in my hearth slab 3 days ago. The mix is curing and feels hard to the touch, but does seem to have a bit of give. Is this normal? I would also like to know if it’s okay to expose it to sun, rain before I am ready to install the firebrick floor?

Thanks very much.
Greg

2

Hey Greg,

Yes, that sounds normal. Keep in mind that the material there is not meant to bear the load, so a little give is fine. If you are more than 3 days out, it’s also fine to uncover it and prepare for the next step of pouring in leveling sand. It will continue to cure underneath the sand layer.

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3

Thanks Matt, I appreciate the quick reply. One follow-up question: Is a drain hole recommended for the red brick frame on the hearth slab? I’m just wondering how rain water that makes its way inside the frame (say due to a crack in the bricks or brick mortar) can drain so that it does not sit in the sand layer.

Thanks again for all your help!
Greg

4

Good question. The only penetration area would be the transition between the hearth and the frame brick at the opening. Everything else is sealed by the arch base with no chance of penetration.

The hearth is meant to “float”—no bond between hearth and framing bricks. If you make the front joint tight to the frame you’ll minimize any moisture penetration.

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