Hi, I’ve just had a new gas fire and Portuguese limestone fire surround fitted. The problem is that the hearth is approx 3 inches from the floor. I’ve been told that this is because the fire is sitting on concrete in the chimney. The fitters told me that if they tried to remove the concrete there may be a void below and it could collapse the opening. So I just need some advise on either how we can lower the fire or what would you suggest to put around the 3” gap below the hearth to cover the gap. The fire is brushed steal.