Staining on your chimney may be one home improvement project that can prove to be difficult to figure out by yourself. Discoloration on a 
chimney doesn’t usually happen because of old age or use. It’s typically a warning that there is an underlying problem. The color of the staining on your chimney can give you a clue as to what the problem is.
So…what color are the stains?
Black, Brown or Green Stains
These stains are usually located closer to the top of the chimney or around “shoulders.” At times they may extend top to bottom over just part of the surface of the chimney. While it’s possible that some black or brownish stains at the very top can be from condensate dripping off a cap, it is more likely (especially where there is no cap) these stains are a sign that mold, mildew and/or algae is growing in the chimney. Mold, mildew, and moss growing on the chimney surface are caused by excess moisture in the chimney structure. It could be growing on the chimney because of a water entry problem due to a clogged gutter causing overflow to run down the chimney. Or it may also be growing on the chimney because of excessive water absorbing into the chimney due to soft brick or mortar or holes in the mortar joints. This along with slow evaporation will lead to vegetative growth that will eventually undermine the mortar of the brick structure. If you notice these dark stains, it is a smart idea to call on a trained professional to evaluate your chimney to identify the source of the problem and recommend
resolutions.
Reddish Rust-like Stains
Rusty reddish stains on the chimney are a sign that a metal chimney component, like a chimney cap or chase cover, is rusting. Rusting of these components will produce pitting and flaking of the metal and will eventually develop holes that will allow damaging water to get into your
chimney.
White Stains (Efflorescence)
White powdery staining is called efflorescence. When water evaporates out of masonry, it leaves behind whitish salt deposits. The staining itself can sometimes be removed, but it is a sign of a more serious condensation or water absorption problem and will likely return if the
problems causing it are not corrected. Water absorption/intrusion of some kind is the root problem and eventually deteriorates bricks and mortar or causes other damage, if it is not stopped. Along with weakening the structure of your chimney, water damage can spread to
your home ruining walls, ceilings and floors.
Pretty much any of the stains can be traced back to a water problem of some kind. Regular inspections to determine necessary maintenance and replacement of deteriorating products will protect your investment and help avoid unexpected costly repairs. Let our trained professionals here at Blue Sky Chimney Sweeps|Bless Your Hearth help determine how water is getting into the chimney and solve the problems before things escalate.