Whether running up an exterior wall or emerging through the roof, the last few feet of chimneys are completely exposed to the wrath of Mother Nature. These positions mean that chimneys are regularly subjected to intense heat, windblown rain, freezing temperatures, and other environmental insults.
The fact that most chimneys sail through decades of such abuse with little or no damage is truly a testimony to the durability of masonry. The one possible chink in the chimney's armor is the cap (or "wash," as it's called in my part of the country).
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