Hi, don’t know if anyone can help me unpick this. We pulled out the gas fireplace that was previously installed and removed everything back to the original chimney breast brickwork. As we did that it became apparent that the person who installed it hacked the right angles off the fireplace brickwork. We are planning on lining the recess with Hardie board, but I am worried that where the board meets at a right angle the void behind it will render the board unstable or prone to break. I