What it means:Too much moisture inside the chimney.
Efflorescence is the white material that appears on brick. It occurs when moisture moves through masonry. That moisture picks up minerals and leaves them behind in the form of tiny crystals. The minerals themselves do no harm, and a small amount of efflorescence is common.
But heavy efflorescence on your chimney is a cause for concern. It’s a sign of moisture inside the chimney—and when that moisture freezes, it can slowly wreck the chimney from the inside out. Even more alarming, your flue liner could be cracked or broken, and deadly combustion gases from your furnace, fireplace or water heater may be leaking into your home.