Stage one flakes brush away easily; stage two tar clings like licorice; stage three forms armor that needs professional tools. Schedule sweeping after summer nesting season, verify brush sizing for liner diameter, and keep written logs for insurance and peace when embers start crackling.
A well-fitted cap blocks downdrafts and protects liners from freeze-split moisture. Screens deter birds, squirrels, and persistent wasps scouting warm spaces. Spark arrestors catch embers on windy nights. Inspect fasteners, mesh gauge, and seal between crown and flue tile so nothing loosens under snow load.