“Freeze-Thaw” Warning: January’s Silent Killer

With its snowcapped roofs and crisp air, winter in Wisconsin is a wonderland for folks who enjoy cross-country skiing, ice skating, and other winter activities. However, while water and snow may appear harmless, they are quite damaging to masonry chimneys. When water freezes into ice, the resulting pressure can silently cause brick and mortar to crack or even shatter. This destructive process, known as the Freeze-Thaw Cycle, can become January’s “silent killer” if left unchecked.

What is the Freeze-Thaw Cycle?

The freeze-thaw cycle occurs when winter rain or melting snow seeps into the porous materials of your chimney—like bricks, mortar joints, and the concrete crown. When temperatures drop, that water freezes and expands. This expansion is like a slow-motion jackhammer, pushing against the masonry from the inside out. When the ice thaws, it leaves larger gaps, allowing even more water to freeze during the next cycle.

How Freeze-Thaw Cycles Affect Chimneys in Wisconsin?

Wisconsin winters are notorious for temperature fluctuations. In the Milwaukee area, it is common to experience several freeze-thaw cycles in a single week. Because masonry is porous, it absorbs moisture like a sponge. Without proper winter protection, a chimney in MKE undergoes hundreds of these practically silent “masonry busters” each season, rapidly accelerating the structure’s deterioration.

Dangers of Freeze-Thaw Damage

One of the biggest dangers of the freeze-thaw process is that minor hairline fractures can quickly turn into deep structural gaps, allowing water to seep deep inside the chimney and compromise the stack’s integrity. As mortar deteriorates, bricks lose their “grip” and can fall off the stack, posing a hazard to your roof or anyone walking below.

Unlike a tornado or hurricane that makes a lot of noise, the freeze-thaw cycle can be just as damaging without making a sound. That’s why it’s often referred to as January’s “silent killer.” It poses other dangers too:

Water Leaks

 Once the exterior masonry is breached, water enters your home, causing mold, rotted wood framing, and stained drywall.

Carbon Monoxide Poisoning

 If the internal flue tiles crack due to freezing, another “silent killer,” deadly carbon monoxide can leak into your living spaces instead of venting out the top of the stack.

Leaning/Tilting Chimney

 Severe internal damage can cause the chimney to pull away from the house or lean.

Chimney Collapse

 In extreme cases, the freeze-thaw process creates more holes than a slice of “Swiss cheese” due to ice damage, putting the entire structure in imminent danger of a collapse.

Signs of Freeze-Thaw Damage

Keep an eye out for these “red flags” this January:

• Spalling: This occurs when the surface of the brick flakes off, crumbles,  or “pops” out.
• Efflorescence: A white, powdery staining on the bricks, which indicates salt-heavy water is moving through the masonry.
• Mortar Deterioration: Sandy or crumbling gaps between the bricks.
• Damp Firebox: Moisture or staining on the walls inside your fireplace.
• Carbon Monoxide Poisoning: Headaches, dizziness, or nausea when using the fireplace.

Repairing Freeze-Thaw Damage

Depending on the extent of the freeze-thaw damage, the repair can be as simple as sealing the crown with a weather-resistant coating. Or it could be more extensive, such as a partial or complete chimney rebuilding.

Chimney Waterproofing

After making the necessary masonry repairs, we recommend waterproofing the chimney to prevent future water damage. Our certified technicians use a professional-grade, vapor-permeable water repellent. This specialized formula allows trapped moisture to escape while creating a moisture-resistant shield that protects the masonry against the damaging effects of rain, ice, and UV exposure.

Call Smokestacks to Prepare Your Chimney for Winter in the MKE

Don’t wait for a leaky chimney to ruin your winter! Lake-effect snow and freezing conditions can be unforgiving for your stack. Let Smokestacks prepare your chimney for the annual freeze-thaw cycle. Our Certified Chimney Professionals® serve the entire Milwaukee Metro area, including Elm Grove, Merton, Whitefish Bay, and Oak Creek, WI. Call Smokestacks today to winterize your chimney and escape January’s “silent killer.”