I have tiled over my existing fire place hearth. The hearth ext. is solid concrete underneath and about 4” thick at its thinnest part. The concrete from below looks as if it is not supported on the end farthest from the fireplace opening. My question is, am I safe putting a my stove (~435 lbs) over the tile where the concrete hearth is. Not sure who to contact to make sure this is safe and not going to collapse.