hi, i hope someone can help me with this, i am quite a novice on DIY. i am building a fitted cupboard in to the alcove. when i tried to drill into the side of the chimney breast to attach wooden batten for my frame, after half and inch into drilling i hit something metal. what could it be? can i drill into it? we don't use any of the fireplaces. they all been boarded up by previous owner. Many thanks..