By James Rodriguez, Central Chimney Service.
Every older chimney looks a little rough up close. The useful skill is telling the difference between a chimney that is simply weathered and one that is actively coming apart, because the second one gets worse on a schedule and the first one does not.
What spalling actually is
Spalling is brick face failure: the outer surface flakes, pops, or sheets off, leaving a rough, lighter-colored, crumbly area behind. It happens when water inside the brick freezes and expands, pushing the hard fired face away from the softer body underneath.
Normal weathering looks different. Weathered brick is darkened, slightly eroded, maybe a little uneven, but the face is intact and hard. If you run a hand over it and nothing comes away, and the profile is still flat, that is age rather than failure.
The five-minute exterior read
Stand back with binoculars and work top to bottom. At the crown, look for cracks and missing corners. In the top courses, look for pale patches where the face has come off — these fail first because they get the most water.
In the mortar joints, look for recessed, sandy, or missing mortar; a joint that has eroded more than about a quarter inch deep is past due for attention. On the shaded north face, look for green or black biological growth, which indicates persistent dampness. At the roofline, look at the flashing for lifted edges, rust, or a bead of tar someone applied instead of doing it properly. And at ground level, look for brick fragments in the gutters or on the ground.
One band deserves particular attention while you are looking: the mortar joints right at the roofline where the chimney passes through. That course takes water shed off the roof plane in addition to direct rain, and it is where we most often find joints eroded well past the condition of the faces above and below. It is also the hardest area to read from the ground, because the gutter line, the roof edge, and the flashing itself all obscure it. If everything else looks like ordinary weathering and the chimney is still taking on water, that band is the first place to check.
Why mortar fails before brick
Mortar is intentionally the sacrificial component. It is designed to be softer than the brick so that movement and moisture damage the joints rather than the units, because repointing joints is a far smaller job than replacing brick.
That design only works if the joints are maintained. Once mortar has eroded, water enters the wall freely, and then the brick starts failing too. A great many of the older masonry chimneys we work on in Joliet are at exactly that transition point — joints gone, brick faces just beginning to go [Observed]. That is the moment where acting is cheapest.
What repair looks like at each stage
Eroded joints with sound brick means tuckpointing: the old mortar is cut out to a proper depth and new mortar is packed in and tooled to match. Critically, the new mortar has to be no harder than the original, or the brick becomes the sacrificial element and starts failing instead.
Localized spalling means cutting out and replacing the affected units. Widespread spalling in the top courses usually means rebuilding from a sound course upward, which is also the natural time to correct a bad crown. Either way, whatever is letting water in above — crown, cap, or flashing — gets fixed first. See chimney repair for how we scope this, and our DIY chimney care guide for the checks you can do yourself.
Getting an honest assessment in Joliet
Masonry is the area where quotes vary most, so get someone to show you the actual defect and explain why the proposed scope matches it. Central Chimney Service is insured and bonded, covers Joliet seven days a week from 7 AM to 7 PM, gives the price up front, and brings 29 years of local experience to the assessment. Call (815) 305-5510.
Frequently asked questions about chimney masonry and spalling brick
Is spalling brick dangerous?
It becomes dangerous when enough face material is lost that the wall’s structural section is reduced, or when spalling reaches the point that individual bricks work loose above a roof or walkway. Early surface spalling is not an emergency, but it is progressive and does not stabilize on its own.
Can I seal spalled brick to stop it getting worse?
Not effectively, and the wrong sealer makes it worse. Once the hard fired face is gone, the exposed body absorbs water even faster, and a film-forming sealer traps that water inside where the next freeze can work on it. Damaged units need replacing, not coating.
What is tuckpointing versus repointing?
In everyday use they are used interchangeably for cutting out deteriorated mortar and filling the joint with fresh mortar. Strictly, tuckpointing originally described a decorative technique using two mortar colors, but almost nobody uses the word that way now.
How do I know if the mortar used is too hard?
You generally do not by eye, which is why it matters who does the work. The signal that it was wrong shows up later: the brick faces adjacent to new joints start spalling while the joints stay perfect. On older soft brick this is a common and avoidable outcome.
Does a chimney need to be rebuilt if the top few courses are bad?
Not the whole chimney. A partial rebuild from the last sound course upward is a standard job, and it is usually paired with recasting the crown since the top is already open. Full rebuilds are for structural problems that run the height of the stack.
Why is only one side of my chimney damaged?
Prevailing weather. The face taking wind-driven rain gets far more water than the sheltered side, and a north face stays damp longer because it dries slowly. Uneven damage across faces is the normal pattern, not a sign of something unusual.
Can masonry repair be done any time of year?
It needs temperatures above roughly forty degrees for mortar to cure properly, and ideally not in direct blazing sun that dries it too fast. In this climate that puts the practical window from spring through early fall.
Should I repair the masonry or the liner first?
Whatever is letting water in gets addressed first, because everything else fails again underneath an active leak. After that, the liner takes priority over cosmetic masonry, since the liner is what makes the appliance safe to operate.
Published August 15, 2026 · Last updated August 9, 2026