What the lakefront climate does to a Waukegan flue
Living at the edge of Lake Michigan means living with a chimney that is wetter and colder than one a few counties inland. The lake throws moisture into the air year round, and in winter that moisture rides the wind straight into the porous brick and mortar of an exposed stack. Water that soaks into masonry on a January afternoon and freezes overnight expands inside every tiny pore and hairline crack, and the next thaw lets a little more water work its way deeper. Repeat that cycle through a Lake County winter and the freeze-thaw grind chews the face off the brick, opens the mortar joints, and lifts the crown a fraction at a time until water has a clear path inside.
The cold does its own kind of harm to the way the chimney drafts. When the air column inside a tall masonry flue chills down on a frigid night, the draft slows, smoke lingers in the flue longer, and a wood fire that is not burning hot enough lays down creosote faster than it would on a milder evening. The glassy, tar-like creosote that builds up in a sluggish flue is the fuel a chimney fire feeds on. So the same lakefront cold that pries at the brick from the outside is encouraging a hazard to grow on the inside, which is why we are so insistent that a Waukegan chimney be swept and looked at before the heating season rather than after something goes wrong.