What are the white stains on a masonry chimney?

Why is There White Staining on My Chimney? - Stained chimney photo

Example of a chimney with white stains.

White staining on a chimney is more than an eyesore, its often an indication that excess moisture has gotten into the chimney masonry. That might not sound serious but water can cause a dramatic amount of damage to your chimney, traditional masonry fireplace, and even your home. Along with removing the white residue, its important to have the source of the problem identified and addressed.

What Causes Staining on a Chimney?

Efflorescence is the name of the white residue on your chimney. It is a powdery or crystallized substance that can develop on brick, stone and block. It is formed when excess moisture in masonry evaporates and leaves behind salt deposit stains. Though white staining is most common, the colour of efflorescence can vary depending on the type of compounds in the masonry. Twenty different kinds of compounds have created crystalline deposits on chimneys with varying colours of staining. Typically, efflorescence is produced by sulfates of sodium, calcium, magnesium, potassium and iron.

Three conditions are necessary for efflorescence to occur:

1. The masonry must contain soluble-salts.

2. Moisture must mix with the salts to create a soluble-solution.

3. The soluble-solution must be able to move through the masonry and evaporate.

While these salt deposits themselves do no harm to your chimney, the moisture that causes them can be very destructive. In most cases, this water gets into chimneys through a missing or cracked chimney cap, cracks in the chimney’s structure or improperly sealed masonry (unsealed brick acts like a sponge, absorbing excess water it comes in contact with). The absence of a chimney liner could also be a cause since one of the functions of a chimney liner is to protect the chimney from the water that is produced from combustion. All of these problems allow water to seep into stone or brick walls. Along with dissolving salt residue, this water can deteriorate the structure of your chimney and cause water damage to your home.

Damage Caused by Excessive Moisture

In the majority of cases, when efflorescence is visible on a chimney it is also present on the brick within the house. Along with these unsightly deposits, the excess moisture may be:

  • Causing the wood that connects with the chimney to rot and mold
  • Damaging the insulation, ceilings, carpet and padding
  • Causing the chimney to prematurely deteriorate, which could result in a leaning or collapsed chimney
  • Cracking or deteriorating the flue lining
  • The longer the problem is left unaddressed, the more significant the damage is likely to be. While efflorescence is not a mold, it forms in the same conditions that are ideal for mold production. Often the two go hand-in-hand.

What You Can Do to Prevent White Staining on your Chimney

Why is There White Staining on My Chimney? - Stained chimney photo

Another example of white stains on the outside of a chimney.

If your chimney has efflorescence, you should have it thoroughly examined by a professional chimney sweep to discover how water is seeping into the masonry and determine the extent of the damage. The chimney technician will be able to suggest ways to solve this problem and, depending on what is discovered, repairs may be suggested to restore the structural integrity of your home and chimney. Since mold is commonly discovered along with efflorescence, you may also want to have all organic material in your home near the chimney closely inspected for mold, allergens and bacteria.

Efflorescence itself will usually wash away overtime from weathering. You can also wash it away. Tough stains can be removed with cleaning products. The most effective products contain muriatic acid (a harsh chemical). You can find simple, step-by-step instructions on many DIY websites to help you remove it.

Only you can prevent damage from spreading by seeking out help from qualified professionals when problems arise. We would love to help you protect your home from extensive water damage. Our professional chimney technicians will do a thorough inspection and share with you what they believe to be the source of the problem, the extent of the damage (inside and outside of the chimney) and suggest the best course of action for correcting and preventing further damage.

Please contact our service department to book a chimney cleaning or annual servicing.

If you have any other questions about chimneys or any other aspect of your fireplace, insert, or stove servicing, please leave a comment below.

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