What older Main Line chimneys are up against
The stone and brick homes that fill Bala Cynwyd and the neighboring Main Line towns were built with serious masonry chimneys, and that heritage cuts both ways. The good news is that these stacks were constructed to a standard you rarely see in newer housing, with thick walls and real craftsmanship. The hard news is that the materials inside them age on a schedule of their own. The clay tile liners common in homes of this era crack and shift over the decades, the mortar joints between the flue tiles open up, and the crown at the very top, which is the chimney's first defense against rain, is often the original concrete cap that has been quietly failing for years. A chimney can look magnificent from the driveway and still be moving flue gas where it has no business going.
Then there is the water, which does more damage to local chimneys than fire ever will. A Pennsylvania winter runs the masonry through endless freeze and thaw cycles, and any water that has soaked into a porous brick, an open joint, or a cracked crown expands every time it freezes and pries the masonry apart a little further with each cold snap. The taller, larger chimneys on these older homes catch and hold a great deal of weather, and on the wooded lots common in Gladwyne and Penn Valley the constant shade keeps the masonry damp long after a storm. The spalling brick, the crumbling crowns, and the white efflorescence staining we see across the Main Line almost always trace back to water that found a way in and a winter that did the rest.