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?
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.
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.