Why a coastal climate is harder on a Westminster chimney than the mild weather suggests
Nobody worries about a chimney in a place that never really freezes, and that is precisely the trap. Westminster sits only a few miles from the open water, and the air that moves across town carries a steady load of salt and moisture. That marine air is corrosive in a slow, patient way. It rusts the metal damper plate until it seizes or rots through, it eats at the galvanized or steel cap and the screws holding it down, and it keeps the masonry of the chimney damp far longer after a rain than the dry inland heat would. Brick and mortar are porous. They drink that moisture in, and over the decades the salt crystallizing inside the pores pushes the surface of the brick apart, leaving the flaking, crumbling faces and the soft, raked-out mortar joints we find on so many of the original tract chimneys here.
The other half of the story is how little these fireplaces actually run. A chimney that burns hard all winter at least dries itself out and gets looked at because the owner is using it constantly. A Westminster fireplace can sit cold and forgotten for ten or eleven months of the year, and a cold, dark, sheltered flue is an open invitation. Birds nest in it in spring, roof rats and the occasional raccoon move in, and the debris they bring plus the leaves and pods that drift down build up on the smoke shelf where no one can see it. Then a cool evening comes, someone strikes a match for the first fire in a year, and the blockage they never knew about sends smoke and carbon monoxide back into the room. The two forces work from opposite ends. Salt air corrodes and softens the chimney from the outside while disuse lets it silt up and grow a nest on the inside, and a flue that goes years without a scan is usually carrying both problems at once.