I have recently whitewashed my brick chimney. It’s irrelevant to the problem but white background color makes efflorescence more noticeable.  After a month of whitewashing, my chimney (January in MA, which is the coldest month) developed yellow efflorescence. My chimney or roof does not seem to be leaking, or is it? I see the efflorescence on random bricks.

Questions I have:

  • Do I have a water leak somewhere? I have a chimney cap, it’s a two floor house, and the chimney is on the first floor. I have three furnaces heating the house and exhaust goes into chimney. When I touch the bricks on cold days, there is moisture. There is no one at home during the day so I keep it at 57F, and at night 63-68F.

  • Is it possible that condensation is forming on the bricks which is causing efflorescence?

  • Finally, do I need to do anything about it? Is it going to deteriorate my chimney, do I need to call a professional, or just ignore it and keep cleaning it. Is there a way of preventing condensation and stopping efflorescence?

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  • What is the RH of your house? The mortar looks wet with liquid moisture signs. You could easily have water seaping into your chimney from the roof and running down the inside of the chimney. You might also just have moisture from the furnace exhaust condensing somewhere on the inside cold surface of the chimney and running back down. Commented Feb 5 at 7:59
  • 1
    You've got way too many questions in one here. Please pick the most important one and edit it down to that one, then ask other questions for the other issues. Maybe start with the "do I need to do anything about it", because if the answer to that is "no", the rest are moot points.
    – FreeMan
    Commented Feb 5 at 13:19
  • Relative Humidity in this room is around 40-43%
    – Supertech
    Commented Feb 5 at 23:56

1 Answer 1


Use exterior chimney brick waterproofing spray or cream. It’s siloxane based. Use as described. It’s looks like your mortar or brick at roof line is taking in water. That water gets behind the chimney flashing and behind the ice and water shield. Cheap fix and you should waterproof the chimney brick and seal coat the crown anyways to prevent issues. Is there any water in the fire place?

  • No there is no water in the fire place. I will call a chimney person to have him a take a look at it.
    – Supertech
    Commented May 5 at 4:16

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