If the brick face on your chimney is flaking off in thin sheets, crumbling at the corners, or leaving a small pile of orange grit on the roof shingles, that is spalling. It is not cosmetic. It is the outer skin of the masonry failing because water got inside the brick and froze there, and in the southwest suburbs the clock on that damage runs from about November through March every single year.
By Daniel Watkins, Noble Chimney Sweepers.
What spalling actually is
Spalling is brick shedding its own face after absorbed water freezes and expands inside it. Fired brick is porous by design, and a healthy chimney sheds the water it takes on before temperatures drop. When the drying path is blocked — by a failed crown, a missing cap, hard modern mortar, or a sealant that trapped moisture in — the water has nowhere to go, so it turns to ice and pushes the face off from the inside.
Why Crest Hill chimneys give up their brick faster than you would expect
A chimney is the only masonry on the house exposed on all four sides, top to bottom, with no soffit above it and no heated interior behind most of its height. Around Crest Hill, the mix of mid-century brick stacks and 1990s-era subdivision chimneys means we see two very different failure patterns on the same street. Older stacks usually lose brick because the original soft mortar was repointed at some point with a hard portland mix that will not flex. Newer chimneys usually lose brick because a thin crown cracked early and has been feeding water straight down into the top eight courses ever since.
The freeze-thaw clock, and why late summer is the window
What makes northern Illinois hard on masonry is not the depth of the cold, it is the number of times we cross the freezing line. A stretch of days that thaws by afternoon and refreezes overnight puts a brick through the expansion cycle again and again, and every cycle takes a little more of the face. Doing the water-control work now, while the masonry is dry and mortar can cure in warm air, is the difference between a repair and a rebuild. Once the stack is wet going into December, nothing productive happens on it until spring.
Water control comes before brick work
Replacing spalled brick without fixing why it spalled buys you a season. Before any face repair, we look at the top of the chimney first: a crown that sheds water past the brick instead of onto it, a cap that keeps rain out of the flue, flashing that actually laps the way it should, and mortar joints that are sound rather than raked out by weather. Our chimney repair and masonry work starts at the top for that reason — fix the source, then fix the damage.
Repointing, replacement, or rebuild
Three honest outcomes, and which one you get depends on how deep the damage runs. If the mortar joints are eroded but the brick faces are intact, repointing with a mix matched to the original mortar is the right call. If a scattered handful of bricks have lost their faces, those get cut out and replaced individually. If the top courses are soft enough that a screwdriver sinks into them, the crown is gone, and the stack has visibly leaned, that section gets taken down and rebuilt. We tell you which of the three you are looking at, and you get the price up front before anything starts.
A note on sealers
Not every waterproofer belongs on a chimney. A film-forming sealer that leaves a shine will stop water from getting in and also stop the water already in the brick from getting out, which accelerates the exact damage you were trying to prevent. Breathable vapor-permeable masonry treatments are the category that works on a chimney, and they go on only after the joints and crown are sound.
What you can check from the ground
Walk the perimeter with binoculars on a clear day. Look for brick faces that have popped off and left a rough recessed pocket, white powdery staining, joints that look recessed compared to their neighbors, and grit collecting in the gutter below the chimney. Our DIY chimney maintenance guide covers what is reasonable to inspect yourself and where the line is. Nothing on that list requires a ladder, and none of it should.
Noble Chimney Sweepers is certified, bonded and insured, owner-operated, and has been working on chimneys in this area for 14 years. We are here 7 days a week, 7 AM to 7 PM. Call (708) 432-5747 to get a look at your masonry before the first freeze, or see current rates on our pricing page.
Frequently asked questions
Is spalling brick dangerous or just ugly?
It is structural over time. Each spalled face exposes the softer interior of the brick to more water, which accelerates the next round of damage. Left alone for several winters, the affected courses lose enough material that the stack can lean or shed loose brick.
Can I just paint or seal over spalled brick?
No. Paint and film-forming sealers trap moisture inside masonry that is already saturated, which makes spalling worse rather than stopping it. Damaged brick has to be repointed or replaced, and any treatment afterward needs to be vapor-permeable.
How many bricks have to fail before it needs repair?
There is no fixed count. What matters is depth and location. A few shallow faces low on the stack can wait a season; anything in the top courses, near the crown, or deep enough to expose the flue behind it should be handled before winter.
Does a chimney cap help with spalling?
Yes, indirectly and significantly. A cap keeps rain out of the flue and off the interior masonry, which cuts the total water load the chimney has to dry out. It does not protect the exterior faces, which is why the crown matters just as much.
What is the difference between the crown and the cap?
The crown is the sloped masonry or concrete slab covering the top of the chimney around the flue tiles. The cap is the metal cover with mesh sides that sits over the flue opening itself. Both control water, and both fail in different ways.
Will repointing match my existing brick?
Mortar color and joint profile can be matched closely, though fresh mortar is lighter until it weathers in over a season or two. For replacement brick, we source the closest available match, and older or discontinued brick sometimes shows a visible difference.
How long does chimney masonry repair take?
Most repointing and partial brick replacement is a one-day job. A rebuild of the upper section usually runs two days, plus cure time before we recommend running a fire.
Should I have the flue swept at the same time?
It is efficient to do both in one visit since we are already on the roof and in the firebox. A sweep and inspection also tells us whether water has been getting into the flue, which changes the repair plan.
Published August 21, 2026