Mokena rarely stays frozen all winter, and that is exactly the problem for your chimney. It is the repeated thaw, not the cold itself, that pries brick and mortar apart.
The mechanism: water that grows when it freezes
Brick and mortar are not solid; they are riddled with tiny pores that drink in water like a sponge. When a chimney gets wet from rain, snowmelt, or condensation, that moisture soaks into the masonry. Then the temperature drops below freezing and the trapped water turns to ice. Here is the crucial physics: water expands by roughly nine percent as it freezes. That expansion has nowhere to go, so it pushes outward on the walls of every pore with surprising force.
One freeze does little harm. The damage is cumulative. Northern Illinois can swing above and below 32 degrees dozens of times in a single season, often within the same day as afternoon sun melts the surface and night refreezes it. Each cycle widens the pores a hair, draws in a little more water next time, and expands again. Over several winters the masonry fatigues from the inside out. This is freeze-thaw damage, and it is the number one reason chimneys in our area need masonry work. A chimney is especially vulnerable because it stands fully exposed on all sides and sits above the roofline, catching driving rain and wet snow that the walls of the house never see. That exposure is why the chimney often shows weather damage long before the rest of the masonry on a home does.
What it looks like from the ground
You can often spot freeze-thaw damage before it becomes serious if you know what to watch for:
- Brick faces that have popped off, flaked, or crumbled, leaving a rough, recessed pockmark.
- Mortar joints that have receded, softened, or washed out so you can see gaps between bricks.
- Pieces of brick or mortar grit collecting on the roof or in the gutter below the chimney.
- A crown with hairline cracks that let water sit and seep rather than shed.
- Bricks that feel loose or sound hollow when tapped.
Left alone, the cycle accelerates. Once water has an easy path in, it reaches the flue liner and the structure behind the facing brick, which turns a cosmetic repair into a structural one. Catching it early is far cheaper, which is why an annual look matters; we document the masonry condition during a chimney inspection so small damage is caught before another winter compounds it.
The fix: repair the damage and keep water out
Stopping freeze-thaw damage is a two-part job. First we repair what the cycles have already broken; then we interrupt the cycle by keeping water from soaking in.
- Repointing rakes out failed mortar joints and packs in fresh mortar matched to the original, restoring the seal between bricks.
- Brick replacement swaps out faces that have crumbled beyond repair so the wall sheds water again instead of holding it.
- Crown repair or rebuild fixes the concrete cap that is supposed to shed water off the top; a cracked crown feeds moisture straight into the masonry below.
- A correctly sized cap keeps rain and snow out of the flue, cutting the moisture load at the source.
- Breathable masonry water repellent lets the chimney release interior moisture as vapor while blocking liquid water from entering the pores, so the freeze has far less to work with.
We handle the structural and water-management side through our chimney masonry repair service, and we work to the NFPA 211 standard so the repairs support safe operation, not just appearance. Owner-operator Jason Lecter has rebuilt plenty of chimneys across chimney service in Mokena that could have been saved with earlier attention, so if you see flaking brick or grit in the gutter, do not wait for spring. For costs on repointing, brick work, or crown repair, see our pricing page.
Frequently asked questions
Why does freeze-thaw damage happen here more than in colder states?
Because our temperatures cross the freezing point repeatedly rather than staying frozen. Each thaw lets water soak in and each freeze expands it, so frequent cycling does more damage than steady deep cold.
How much does one freeze actually damage brick?
Very little on its own. The harm is cumulative across dozens of cycles a season, which is why chimneys show their age after several winters rather than overnight.
Can I just paint or seal the chimney myself?
Ordinary paint traps moisture inside and makes freeze-thaw worse. A breathable masonry repellent is the right product, and it should go on sound masonry after any needed repairs, not over crumbling brick.
Is flaking brick a structural problem?
It can become one. Once water reaches the structure and liner behind the facing brick, a cosmetic issue turns structural, so early repointing and brick replacement are the economical path.
How do I know if my crown is causing the damage?
A crown with cracks or a flat, un-shedding surface funnels water into the masonry below. We check the crown during inspection and repair or rebuild it if it is feeding the problem.
How often should the chimney be inspected for this?
Once a year, ideally in fall before the freeze-thaw season. An annual inspection catches small masonry damage while the repair is still minor and affordable.
Published October 26, 2026.
