Masonry chimneys fail from the outside in, and almost always because of water. Ace Chimney Service repairs tuckpointing, spalled brick, failed flashing, and deteriorated crowns on homes across Crystal Lake and McHenry County.
Why chimneys in northern Illinois deteriorate
A chimney is the most exposed masonry on a house. It stands clear of the roof on all four sides, takes weather from every direction, and has no overhang protecting it. Then winter goes to work on it.
Water absorbed into brick and mortar expands by roughly nine percent when it freezes. Between November and March the temperature here crosses freezing again and again, and each cycle opens the joints a fraction more. Over years, mortar turns to sand and brick faces break away. Nothing about that is unusual — it is the normal life cycle of exposed masonry in this climate, and the only question is whether it gets addressed while the repair is still small.
Repairs we carry out
Tuckpointing and repointing
Failed mortar is ground out to a sound depth and replaced with new mortar matched to the original. Done properly this restores the joint’s weather seal and structural bond. Done badly — smeared over the surface without cutting out the old joint — it looks fine for a season and then falls out.
Brick replacement and partial rebuilds
Where brick faces have spalled away, individual units are cut out and replaced. Where the top courses have gone entirely, a rebuild from the roofline up is usually the sensible fix, and considerably less disruptive than taking the whole stack down.
Crown repair
The crown is the concrete slab across the top of the chimney. It sheds water off the masonry, and when it cracks, water runs straight down inside the structure. Crowns are covered in more detail on our caps and crowns page.
Flashing and leaks
Most chimney leaks are not chimney problems at all — they are flashing problems. Flashing is the metal seal where the chimney passes through the roof, and on almost every Crystal Lake home it is a two-part system: step flashing woven into each course of shingles, and counter-flashing bent into a cut in the mortar joint so it laps over the top. Done that way, water runs down the roof and off the brick. Skip a layer, or seal the joint with a bead of caulk or a smear of roofing tar instead, and it will leak again within a few seasons — usually worse, because the patch hardens and cracks through our freeze-thaw winters.
We see the same failures across McHenry County: galvanised step flashing rusted through, counter-flashing that has pulled out of its mortar groove, and wide chimneys with no cricket, so meltwater pools against the back wall instead of draining around it. A few signs that point to flashing — rather than the crown or cap — as the culprit:
- Brown ceiling or wall stains near the chimney chase, often showing only after wind-driven rain or snowmelt
- Damp drywall, peeling paint, or a musty smell in the attic around the chimney penetration
- Hardened black tar, open gaps, or daylight where the metal meets the brick
When flashing is the cause we do not caulk over it — we reflash it properly: new step flashing tucked under the shingles, counter-flashing set into a freshly cut groove in the mortar, and a cricket added behind wider stacks to send water around them. In quality aluminium, copper, or lead, a proper reflash lasts decades rather than seasons.
Waterproofing
Once the masonry is sound, a breathable water repellent keeps water out while still letting vapour escape. The order matters: repair first, waterproof second. Sealing damaged masonry traps moisture where it does the most harm.
Repair or replace?
Honest answer: it depends on how far it has gone, and you are entitled to see the evidence before deciding. We photograph what we find and explain what each option actually buys you. Surface deterioration on an otherwise sound stack is a repair. A chimney that has lost its structural integrity, is leaning, or has damage running the full height is usually a rebuild, and patching it is throwing money away.
Damage inside the flue is a separate question from the masonry outside it. If the liner has cracked, relining is what restores a safe exhaust path. A Level 2 inspection is how we tell the two apart.
Local, and available seven days
We work from Crystal Lake across McHenry County — Lake in the Hills, Algonquin, Cary, Woodstock, McHenry, Huntley and the towns between. Hours are 7am to 7pm, seven days a week.
Call (815) 320-0883 or request a visit online. Repair pricing is published on our pricing page.
Chimney flashing: the most common source of leaks
When a chimney leaks, homeowners assume the masonry has failed. Far more often the water is getting in through the flashing — the metal that seals the joint where the chimney passes through the roof. The chimney and the roof are two structures that expand, contract, and settle at different rates, and the flashing is the flexible seal that bridges that moving joint. Get it wrong and no amount of masonry work will keep the ceiling dry.
The three parts of a proper flashing job
A flashing system that actually lasts is not one piece of metal and a tube of sealant. It is three layered components:
- Base (apron) flashing — an L-shaped piece across the low side of the chimney that carries water down onto the shingles.
- Step flashing — individual bent pieces woven in behind each course of shingles up both sides, so every shingle overlaps the metal below it. Water can never find a continuous seam to follow.
- Counter-flashing — a second layer let into a groove cut in the mortar joint (a “reglet”), then folded down over the top of the step flashing. This is the piece that makes the difference: because it is embedded into the masonry rather than surface-sealed against it, water cannot run behind it.
Why most flashing fails
Nearly every flashing leak we trace in Crystal Lake comes down to one of three shortcuts. The first is caulk instead of counter-flashing — a bead of roofing sealant smeared where the metal meets the brick. It looks fine for a season or two, then the sun and freeze-thaw crack it and the water pours straight in. The second is rusted galvanized flashing: older galvanized steel corrodes through, staining the masonry with rust streaks on its way to failing. The third is movement — flashing that was never cut into the mortar simply works loose as the roof and chimney shift over the years.
Signs your flashing is the problem
Water stains on the ceiling or in the attic near the chimney, damp patches on the chimney breast after rain, rusty streaks running down the exterior brick, or peeling paint on the wall below the chimney all point to flashing rather than the flue or crown. Because water travels along framing before it drips, the stain is often several feet from the actual leak — which is why we trace it rather than guess.
Reflash properly, don’t re-seal
When flashing has failed, the durable fix is to reflash: cut a fresh reglet into the mortar, install new step and counter-flashing in corrosion-resistant metal, and tie it into the shingles the right way. Re-sealing old, loose flashing with more caulk only resets the clock on the same leak. On wider chimneys we also add a cricket — a small peaked saddle behind the chimney that splits water around it instead of letting it pond against the back wall. Flashing and its seal at the top of the stack work together with a sound crown and cap; a chimney inspection pins down exactly where the water is entering before any work begins.
Frequently Asked Questions
How do I know if my chimney needs tuckpointing?
Look at the mortar joints. If you can scratch mortar out with a screwdriver, if joints are recessed and crumbling, or if you find sand and grit at the base of the stack, the joints have failed and need repointing.
What causes brick to flake and crumble?
Spalling. Water soaks into the brick, freezes, and expands, breaking the face off. Northern Illinois runs through dozens of freeze-thaw cycles a winter, which is why it is so common here.
Can you repair just part of a chimney?
Often yes. If the damage is confined to the top few courses, a partial rebuild from the roofline up is far cheaper than a full rebuild and lasts just as well.
What is flashing and why does it leak?
Flashing is the metal seal where the chimney passes through the roof. It is the most common source of chimney leaks, and it usually fails because it was sealed with caulk instead of properly stepped and counter-flashed into the mortar joints.
Is a leaning chimney dangerous?
Treat it as urgent. A lean usually means a footing or structural problem rather than a surface one, and it can end with masonry coming down. Stop using the fireplace and have it looked at.
Will waterproofing stop my chimney deteriorating?
It helps a great deal once the masonry is sound, but it is not a substitute for repair. Sealing over failed joints traps moisture inside. Repoint first, then waterproof.
How long does masonry repair take?
Repointing a typical stack takes a day or two. A partial rebuild is usually two to three days. Mortar also needs reasonable temperatures to cure, so deep winter work sometimes has to wait.
Do you match existing brick and mortar?
We match as closely as the available materials allow, in both colour and mortar profile. On older Crystal Lake homes an exact match is not always possible, but a careful blend is rarely noticeable from the ground.
Published: July 24, 2026