 you know, cosmetic work that you see, the smalling brick chipping off, or if you've got cracks in the brick, of course. But a lot of folks don't understand that you have a flue liner that's a clay terracotta flue liner that goes up inside of the chimney, and that's what cracks and can't crack. If you want to have a great draft that's pulling and making sure none of the smoke or dangerous chemicals is coming back into the house, there can't be any cracks in these terracotta flue tiles that go up from the inside.