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Brick stains

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I sometimes see creosote stains like that when the chimney flashing has been leaking and the crud from around the top of the chimney leaks down the outside past the flashing.

Most older brick chimneys I see have a brick liner, with a space between the inner and the outer courses. The mortar is usually falling out, and they can't be trusted.

This '57 chimney must be saturated with creosote. It looks like it was oozing out thru the mortar joints. It now has a metal liner and is being used for gas appliances. But the flammable crud is still there. [:-thumbd]

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This can also happen when someone swaps out a standard furnace for a higher efficiency furnace and they do not upgrade the same chimney connection. The new furnace discharges cooler combustion gases that do not adequately exit the top of the chimney and the result is condensation that causes visible effloressence and staining. It mostly occurs on chimneys that are located on exterior walls but I have seen it happen on exposed chimneys in attic areas when the attic is well insulated and ventilated.

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Yeah, I agree with both theories; probably a cracked crown and/or lots of condensation in the stack due to an orphaned water heater or some such. There probably isn't any clay liner and the mortar is breaking down. Bet you could reach into the mouth of that stack from the roof, slide your finger along a mortared joint and the mortar would just fall out of the joint like dry corn starch.

If the mortar is degrading due to the lack of a lining and a failed crown, fixing the crown and lining it with a metal liner will slow degradation but won't impart any strength to the stack. Neither will tuckpointing it and it will simply be a big weapon waiting to drop projectiles one-by-one. They should probably start thinking about getting a cast-in-place liner to restore strength to the stack.








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