Bricks crack for five distinct reasons, and the repair strategy is different for each. The five causes are freeze-thaw saturation, mortar that is harder than the brick it contacts, foundation settlement, steel lintel rust, and structural movement from loads or lateral pressure. Knowing which one is driving the damage determines whether the job is a straightforward tuckpointing visit, a lintel replacement, or something that needs a structural assessment before any masonry work begins.
This post walks through each cause, how to identify it by the crack pattern and location, and what the correct repair looks like. If you are seeing cracks on your wall and want to know which category applies, start here.
Why Do Bricks Crack From Freeze-Thaw Cycling?
Water expands approximately 9 percent by volume when it freezes. That single fact explains more Chicagoland masonry damage than any other.
When mortar joints have eroded - even slightly, even just 1/4 inch recessed from the brick face - they create a channel where water pools. In a Northern Illinois winter with dozens of freeze-thaw cycles, that water freezes and expands inside the joint, then thaws and pulls back, then freezes again. Each cycle widens the crack. After several winters the crack is wide enough to let significantly more water in with the next rain. The process accelerates. The Great Lakes region is documented as a high freeze-thaw zone, and the density of those cycles in a Chicago winter is what separates our climate from regions where masonry survives neglect longer.
The damage pattern from freeze-thaw saturation is usually uniform across an exposed wall face, particularly on north-facing and west-facing surfaces that receive less sun and stay damp longer after rain and snowmelt. Widespread fine cracking in the mortar joints themselves - not through the brick bodies - and mortar that crumbles when touched are the visual signs. The bricks may show efflorescence: white salt deposits where moisture has been migrating repeatedly through the wall.
On Winnetka homes near Lake Michigan, east-facing facades take a compounded version of this damage. Moisture-laden air off the lake drives water into joints all season, and the rapid temperature swings between daytime and overnight accelerate the cycle. Our tuckpointing work along the Sheridan Road corridor involves walls where east-facing joint erosion is running two to three times faster than the protected west face of the same home.
The fix is straightforward but requires doing it right: remove deteriorated mortar to a minimum 3/4-inch depth per BIA Technical Note 7B, then pack fresh mortar matched to the compressive strength of the original. Shallow repointing - scraping the surface and applying a thin skin of new mortar - fails within two or three seasons because the new mortar has no bond depth to hold against the forces working on it.
For a detailed look at how freeze-thaw damage appears in spring and how to read its severity, see What Causes Brick Spalling and How to Prevent It.
The Mortar-Harder-Than-the-Brick Problem
This is the most preventable category of brick cracking, and also among the most common on older Chicagoland homes.
Brick masonry from before roughly 1920 used soft common brick and lime-based mortar. The mortar was intentionally softer than the brick it joined - ASTM C270 sets Type O mortar at a minimum compressive strength of 350 PSI, while the brick around it may test at 1,500 to 2,500 PSI. That differential was engineered into the system. When the wall moves from temperature cycling or minor settlement, stress travels through the path of least resistance: the mortar joint. The joint flexes and slowly erodes over decades. The brick is protected.
Evanston has the oldest residential masonry stock on the North Shore, with homes dating to the 1890s and many from the early 1900s. The city also has the longest history of repair contractors applying Portland cement mortar to those same homes. Portland cement mortar runs approximately 2,500 to 3,000 PSI - harder than the soft common brick it was applied over. The result, documented on hundreds of Evanston facades, is spalling: thin flakes of brick face popping off at the joint edges where the stress can no longer escape through the mortar. This pattern accelerates with each winter.
As NPS Preservation Brief 2 states, mortar must be softer than the masonry units it bonds. This is not a preference - it is the fundamental compatibility rule that determines whether a repair protects the wall or destroys it.
The identification test: look at the joint edges. If the mortar looks hard and uniformly gray, and the brick immediately adjacent to it is flaking or showing concave depressions, hard mortar is the likely cause. Original lime mortar on an unrepaired wall is lighter in color, slightly sandy in texture, and weathers back from the brick face gradually over decades without causing face loss.
The repair requires removing the incompatible mortar first - carefully, with narrow grinding tools and hand chisels to avoid damaging the soft brick edges - then replacing it with lime-based mortar matched to the original. On Evanston greystones, which use Indiana limestone facing over common brick backing, the limestone joints and brick joints require different mortar formulations.
For a full explanation of mortar types and which situations call for each, see Type N vs. Type S Mortar: Which Does Your Wall Need?
Foundation Settlement and the Stair-Step Crack
Foundation settlement is responsible for the most recognizable crack pattern in brick masonry: the stair-step crack, which follows the mortar joints diagonally at roughly 45 degrees, typically starting at a corner or an opening and working its way upward or outward.
The mechanism is differential settlement. One section of the foundation has dropped or shifted more than an adjacent section. The brick wall above has to accommodate that movement through the weakest path: the mortar joints.
Northbrook homes from the 1960s and 1970s building boom show this pattern regularly on attached and detached garages. Garage foundations are typically shallower than the main house foundation, and the large unsupported span above the garage door opening concentrates stress at the corners. Northbrook’s median build date is 1968, placing many garages at 55 to 60 years of service on foundations that were never engineered to the same depth as the house. Soil movement and frost heave work on the shallower footer year after year. We see stair-step cracking at garage corners and horizontal cracking directly above the door lintel on a significant share of Northbrook properties we assess from this era.
Highland Park adds a geographic variable: homes built near the ravine edges sit on sandy or disturbed soil that compacts and shifts. Differential settlement on ravine-adjacent properties can affect not just the garage but the main foundation walls and chimneys as well.
The critical question with settlement cracking is whether the movement is active or stabilized. Active movement needs a structural assessment before masonry repair, because repointing cracks that are still opening will simply reopen. Stabilized movement, where soil has compacted and reached equilibrium, can be repaired with confidence that the work will hold.
A simple activity test: mark the ends of a crack with pencil and date the marks. Check after 30 and 60 days. Any extension of the crack indicates active movement. Fresh, sharp crack edges suggest recent movement; rounded, weathered edges with organic growth suggest older, stabilized movement.
For a detailed look at what different crack patterns mean and how to assess them, see How to Read Cracks in a Brick Wall. For the specific stair-step pattern, see Stair-Step Cracks in Brick: What They Mean.
Steel Lintel Rust: The Hidden Cause That Looks Like Cracking
Steel lintels span the openings above windows and doors in brick veneer construction, carrying the weight of the brick courses above each opening. On most Chicagoland homes from the 1950s through the 1980s, these lintels are standard steel angle iron - bare or minimally protected, now 40 to 70 years old.
Steel corrodes when moisture reaches it. Corroding steel does not just weaken - it expands. That expansion pushes the brick courses above the lintel outward, cracking the mortar joints and eventually displacing individual bricks. The recognizable pattern: horizontal cracking in the mortar joint directly above the window or door, sometimes with rust staining visible on the brick face below, and often a slight outward displacement of the brick courses above the opening.
Deerfield’s colonial and split-level homes from the 1960s and 1970s are exactly the age cohort where lintel rust is most active. The city’s median build date is 1970, and Deerfield city-content data documents window and door lintel rust causing brick displacement as the top masonry problem - the why being straightforward: steel lintels on homes from this era are now past 50 years of service, often installed with minimal mortar cover over the steel, and they have been taking on moisture through eroded joint covers above them. The older the building and the thinner the original cover, the faster the corrosion advances.
The mistake homeowners and less experienced contractors make is to repoint the cracked mortar above the window and call it done. Repointing does not stop the lintel from expanding. Within one or two seasons the fresh mortar cracks again as the corrosion continues. The only fix is to remove the affected brick courses, replace the lintel with a new primed or galvanized steel angle, and reset the brick with proper mortar cover over the new metal.
Lintel replacement with brick reset runs $2,000 to $5,000 depending on the opening size, the number of brick courses affected, and brick matching difficulty. It is not the cheapest repair on this list, but it is the only one that actually addresses the cause.
For more on how to identify lintel failure and what the replacement process involves, see Lintel Repair: Steel and Stone Above Windows and Doors.
Structural Movement: Loads, Lateral Pressure, and Bowing Walls
The fifth cause of cracked brick is less common than the first four but more serious when it occurs: structural movement from loads the wall was not designed to carry, from lateral pressure behind a retaining section, or from failure of the wall ties that connect veneer to structure.
A brick veneer wall is not self-supporting - it is anchored to the structure behind it with metal wall ties embedded in mortar courses. When those ties corrode and fail, the veneer can begin to separate from the backing structure. This appears as a gradual outward lean or bow in the wall face, sometimes with horizontal cracking at the course where tie failure has concentrated movement. For the full diagnostic on this, see Solid Brick vs. Brick Veneer and Bowing and Bulging Brick Walls.
Evanston two-flats and three-flats that have deferred masonry maintenance for decades show this pattern. When individual owners share a building and maintenance decisions require coordination, repairs are often postponed longer than on single-family homes. What starts as simple joint erosion progresses to water infiltration into the wall cavity, tie corrosion, and eventually structural veneer movement. By the time the problem is visible from the street - an obvious bow or lean in the brick face - the underlying tie system has been compromised for years.
Lateral pressure from soil is a different mechanism that affects below-grade walls and low retaining sections. Where soil is pushing against a brick or block foundation wall, horizontal cracking at mid-height of the wall indicates the wall is deflecting under the soil load. This is a structural condition that may require wall anchors or helical piers as part of the repair scope, not just tuckpointing. See Retaining Wall Repair: Brick and Stone for that specific failure mode.
The key diagnostic: if a wall is out of plane - bowing, leaning, or tilting in a way visible to the eye or measurable with a level - that is structural movement, not just mortar failure.
How the Five Causes Look Different on the Same Block
Multiple causes can appear on the same house. A Deerfield colonial from 1975 might show:
- Widespread joint erosion from freeze-thaw on the north and west facades (Cause 1)
- A 1985 repointing job with Portland cement mortar that has been spalling the brick at joint edges for 20 years (Cause 2)
- Stair-step cracking at the garage wall corners from shallow foundation settlement (Cause 3)
- Horizontal cracking above two window openings where steel lintels are rusting (Cause 4)
All four on one property. Each requires a different repair sequence: proper tuckpointing for freeze-thaw damage; lime-based mortar to replace the hard Portland repointing; stability assessment before touching the settlement cracks; lintel replacement for the rust cracks.
Treating all four with one “repoint everything” scope misses the lintel rust entirely and potentially repoints active settlement cracks that will reopen. This is why a free on-site inspection before any scope is written matters.
Evanston: Soft Brick and a Long History of Wrong Repairs
Evanston concentrates several of these problems in one dense housing stock.
The city has the oldest residential masonry on the North Shore - median home built in 1939, with many homes predating 1920. It also has a documented pattern of prior Portland cement repairs that are now the primary source of brick damage. The city’s greystones use Indiana limestone facing on the front facade with soft common brick on the side and rear walls, meaning different repair specifications apply to different faces of the same building.
On a greystone near Davis Street, we typically see: limestone joints that need a soft NHL lime mortar; soft common brick on the rear and party walls that needs Type N or Type O; and Portland cement patches from previous work that need to come out before they cause more face loss.
For Evanston masonry repair, the standard protocol is mortar analysis before any work: test the original, test any previous repairs, and confirm hardness relative to the brick. BIA Technical Note 8 mortar selection guidance is the starting reference.
Northbrook: Garage Walls and Builder-Grade Mortar at End of Life
Northbrook’s housing stock from the 1960s through the 1980s was built with hard machine-pressed brick and standard builder-grade mortar. The mortar is not inherently incompatible with the brick - unlike the lime/Portland problem on older soft brick - but after 40 to 60 years of freeze-thaw cycling, it has reached the end of its service life. Joints are receding, cracking, and losing their weather seal.
The builder-grade mortar used during Northbrook’s post-war construction boom was adequate when installed, not premium. The brick has decades of life left; the joints are the weak link now. For attached and detached garages, the concern escalates because garage foundations are typically shallower than the main house and the above-door span is large. Frost heave on a shallow footer, combined with the structural stress of the wide opening, produces the stair-step corner cracks and horizontal above-door cracks described in the settlement section.
On a Northbrook masonry repair visit, we assess the main house walls and the garage walls separately - different causes, different urgency levels, and sometimes different mortar specifications if the garage was built at a different time than the house.
Deerfield: Lintel Rust as the Primary Driver
Of the communities we see most frequently in Lake County, Deerfield has the highest concentration of lintel-rust-driven cracking. The reason is the construction cohort: Deerfield’s median home was built in 1970. Steel lintels installed in 1965 to 1980 are now 45 to 60 years old, often with minimal mortar cover over the steel - a common production shortcut of that era - and the horizontal joints above windows and doors on many homes are showing the horizontal crack-plus-rust-stain signature.
Left unaddressed, lintel rust advances in one direction: worse. The steel continues to corrode and expand. The displaced brick courses shift further outward. Eventually the mortar above the lintel fails completely and the displaced bricks are held only by friction and gravity - a structural safety concern on upper-story windows.
On a recent project near Deerfield Road, we replaced steel lintels above three window openings on a 1975 colonial, reset the displaced brick, and tuckpointed the surrounding facade. Had the lintel rust been left another five years, brick replacement would have extended to more courses and brick sourcing difficulty would have increased. For the full lintel-to-brick repair process, see the lintel repair post linked earlier in this article.
Reading Your Wall Before You Call Anyone
A homeowner who can read basic crack signatures has a better conversation with any contractor. The quick field assessment:
Follow the mortar joints, not the brick. Cracking that follows joints is almost always mortar-related. Cracks running through brick bodies indicate structural movement or severe freeze-thaw saturation.
Location relative to openings. Horizontal cracking above a window or door with rust staining below it is lintel rust until proven otherwise. Diagonal stair-step cracking from a wall corner is settlement.
Edge condition. Fresh, sharp edges suggest recent movement. Rounded, weathered edges with organic growth suggest older, stabilized movement.
Uniformity. Widespread fine cracking across a full facade - especially north or east - points to freeze-thaw saturation. Localized cracking around one window points to a specific structural cause.
Brick face condition near joints. Flaking at joint edges on an older home points to hard mortar over soft brick.
None of these replace a professional assessment, but they help you describe what you are seeing accurately, which produces a faster estimate.
Getting It Right the First Time
Five causes, five different repair approaches. The most expensive masonry repairs we complete are usually jobs where a previous contractor applied the wrong fix - repointing active settlement cracks, applying Portland cement over soft brick, or chasing a lintel-rust crack with mortar fills that reopened the next season.
Delta - Masonry and Tuckpointing has been working across Chicagoland’s North Shore and northwest suburbs since 1987. Every job starts with a free on-site inspection that identifies the cause before a scope is written. Call (847) 713-1648 or request an estimate online.
We serve Deerfield, Highland Park, Winnetka, and communities across Lake County and the North Shore. Written estimate before any work begins. No surprises.
Hard Portland cement mortar on pre-1920 soft brick does not protect the wall - it transfers the damage from the mortar joint directly into the brick face.