It's not supporting the chimney breast at this portion. You can drill pilot holes to a few inches thick and then bolster the top layer of the structural hearth a way to allow you to fit boards above. Or borrow an SDS chisel.
@rodabod started
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It's not supporting the chimney breast at this portion. You can drill pilot holes to a few inches thick and then bolster the top layer of the structural hearth a way to allow you to fit boards above. Or borrow an SDS chisel.