# What do you think is causing this



## dom-mas (Nov 26, 2011)

builditguy said:


> If the house isn't very old, the furnaces will not be vented in the chimney. High effenciency furnaces will have their own pvc vents.
> .


SHOULD have their own vents


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## JJMasonry (Feb 4, 2014)

I don't think anyone would have vented high efficiency furnace through the chimney since they need two PVC pipes, one for intake and one for exhaust.
It does look like some serious moisture leakage causing the efflorescence.


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## CanCritter (Feb 9, 2010)

moisture intrusion..seal caps and clean..wouldn't hurt to seal entire chimney...
flue liner break and moisture create black stains
my experience with efflorescence is masonry has gotten wet before cureing or water intrusion


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## dom-mas (Nov 26, 2011)

CanCritter said:


> ..
> flue liner break and moisture create black stains


Never seen that. In my experience chimneys with exhaust gas leaks have very crumbly, often almost hollow units and HEAVY white buildup with large crystalline structure. Not like effloresence which is more powdery


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## JBM (Mar 31, 2011)

I visited a development where the corner of all the chimneys were wet where the 8x8 ran up. All the houses were gas with no liner in the flues. People were getting wetness seeping at the bottom of the cellar blockwork. And white chaulky stuff up the whole length of the chimneys.


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## fjn (Aug 17, 2011)

I'm not sure if a cracked liner or eroded mortar between a liner or two would have such a pronounced effect. I would be of the opinion that the strong draft of the chimney would disallow rising gas / moisture to do what is seen in the pictures .


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## CanCritter (Feb 9, 2010)

dom-mas said:


> Never seen that. In my experience chimneys with exhaust gas leaks have very crumbly, often almost hollow units and HEAVY white buildup with large crystalline structure. Not like effloresence which is more powdery


Domas is right...was referring to wood burning...gas would follow the lead above ..appoligies


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## dom-mas (Nov 26, 2011)

fjn said:


> I'm not sure if a cracked liner or eroded mortar between a liner or two would have such a pronounced effect. I would be of the opinion that the strong draft of the chimney would disallow rising gas / moisture to do what is seen in the pictures .


I've seen it numerous times in chimneys that have cheap flex liners for gas fireplaces. The flex liner rips and gas exhaust escapes into the surrounding masonry and everything goes really white and the units just crumble in your hand


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