What a Jersey City year does to a chimney
The chimney is one of the most exposed parts of any Jersey City home, and the local climate works on it from every angle. Summer brings humid heat and the hard, fast thunderstorms that drive rain sideways against a stack standing well above the roofline. Fall and winter bring the real damage, because once water has soaked into the masonry, the freeze-thaw cycling of a Hudson County winter takes over. Water trapped in a brick or a mortar joint expands as it freezes, prying the joint a little wider, and repeats that with every cold snap until the joint opens, the brick face spalls, and the crown develops the hairline cracks that let still more water in.
Burning adds its own wear from the inside. Every wood fire deposits creosote on the flue walls, and on the shared and oversized flues common in older Jersey City buildings, a fire that drafts poorly deposits it faster. Gas and oil appliances leave their own acidic residue that quietly eats at an old clay liner and at the mortar joints between the tiles. So the chimney is attacked from both sides at once, weather working in from the outside and combustion working out from the inside, and the structure in the middle is the brick-and-tile shaft that has to keep the smoke in and the water out. Catching that wear while it is still a repair, rather than after a liner has failed or a crown has let water into the framing, is the entire argument for a regular look.