Hello, The chimney goes right up through the center of my house. We are doing some remodeling and now want the entire chimney to be exposed. It used to be behind a wall. It is 17x17 block. The problem is that there is a gap of about 3" all the way around it where it comes from the basement up to the 1st floor. There is no fire hazard as there is no burning in the basement. Any ideas/experience on sealing the gap? Thanks!