Stair-step cracks in brick follow the mortar joints diagonally and signal differential movement in the wall or foundation. Most are cosmetic once the movement has stopped. A crack narrower than 1/8 inch that has not changed in two or more seasons can be repointed. A crack wider than 1/4 inch, or any crack that is actively growing, needs professional assessment before repair.
What makes stair-step cracking instructive is that it appears on both the oldest and newest housing stock, for different reasons. A 1938 Lincolnwood two-flat cracks from decades of differential settlement between the main block and a rear addition. A 1994 Gurnee colonial cracks at corners because fill soil beneath its footings is still compacting. Same pattern on the wall. Different cause, different urgency, different repair approach.
Why Stair-Step Cracks Follow the Mortar Joints
Brick masonry is not monolithic. It is an assembly of individual units bound by mortar joints, and those joints are the deliberate weak point in the system. A well-specified mortar is intentionally softer than the brick it joins - ASTM C270 minimum compressive strengths reflect this hierarchy: Type O mortar at 350 PSI minimum works alongside soft historic brick that may test at 1,500 PSI or higher. The differential is designed in, so that when the wall moves, the joint fractures first and the brick is protected.
When a section of a wall shifts, the stress travels through the path of least resistance. In brick masonry, that path is the mortar joint. The stress does not cut through the center of a brick if it can travel along a joint instead.
The stair-step pattern reflects diagonal movement. Picture a grid: horizontal joints and vertical joints, staggered by the running bond. A diagonal force - one corner of a foundation dropping while the other stays level - creates a crack that travels diagonally through the grid. It steps from the end of one horizontal joint to the vertical joint above or below it, then steps again. The result is a staircase.
The direction and geometry of the steps tell you about the direction of movement. A crack that steps upward from left to right and opens at the top tells a different story than one that steps upward from right to left. The open end is where the two sections of wall have moved apart; the tight end is where movement is minimal.
For a broader guide on reading all crack types, see How to Read Cracks in a Brick Wall. Stair-step cracks are most informative when you understand how they differ from vertical cracks, diagonal cracks running through the brick units, and horizontal cracks.
Settlement vs. Frost Heave
The two most common causes of stair-step cracking in Chicagoland masonry are differential settlement and frost heave. They look similar in the wall but behave differently over time.
Differential Settlement
Settlement happens when the soil under a foundation compresses or shifts unevenly. In Chicago’s north and northwest suburbs, this is a normal part of a building’s life cycle. Clay soils in the region expand and contract with moisture changes. Old buildings with rubble-stone footings settled incrementally over their first few decades as loads consolidated the soil beneath them.
The classic settlement signature: a stair-step crack that opens wider at the top and tapers toward the bottom. The open top reflects the section that dropped - one part descended relative to the adjacent section.
Settlement that completed decades ago is different from active settlement. A crack that opened 40 years ago when a tree root was removed, or when a water main leak saturated the soil beneath one corner, may have been stable ever since. Monitoring tells you whether the crack is live.
Active settlement is a different matter. Cracks that are growing, that show fresh crumbling at the edges, or that correspond to new interior symptoms like sticking doors or sloping floors deserve structural evaluation, not just repointing.
Frost Heave
Frost heave is a seasonal process specific to climates with repeated freeze-thaw cycles. The Chicago region experiences dozens of freeze-thaw cycles each winter, and the Great Lakes region is documented as a high freeze-thaw zone. In poorly drained soils where water accumulates beneath a foundation or slab, frost heave can push masonry elements upward by measurable amounts.
Frost heave cracking is found at the base of brick walls, at stoops and front steps, at the transition between a main structure and an addition, and at exterior stair stringers. The crack pattern mirrors settlement cracking in its stair-step form, but the seasonality is diagnostic: frost heave cracks open in late winter and early spring, then partially close as the ground thaws.
If you check a crack in February and again in July and the width changes substantially, frost heave is the likely driver. Repeated frost heave can widen cracks incrementally season by season even if each individual heave partially reverses.
Improving drainage around the base of the wall reduces frost heave over time. If water does not accumulate against the foundation, the soil does not saturate and freeze with the same force.
Where Stair-Step Cracks Appear on Chicagoland Homes
Certain locations on a house are more prone to stair-step cracking than others. Knowing where to look makes a self-inspection more useful.
Des Plaines: Clay Soil and O’Hare Vibration
Des Plaines combines two stair-step crack drivers not found together in other communities. The city sits on heavy clay soil that expands when saturated and contracts when dry - that seasonal cycle creates foundation movement, and the walls above translate it into the characteristic stair-step pattern. Foundation tuckpointing here is rarely complete without also addressing drainage grading to reduce how much the clay saturates in spring. The median Des Plaines home was built in 1965, placing most of the housing stock at the 55- to 75-year mark where foundation mortar maintenance is due.
The second driver is low-frequency vibration from O’Hare flight paths. Homes near the airport experience cumulative vibration fatigue from decades of aircraft operations. This vibration gradually loosens mortar bonds and produces stair-step cracking at upper stories and around window lintels - a pattern that looks like settlement but originates from vibration, not soil movement. When you see step cracking primarily on the upper portion of the wall rather than at the foundation on a Des Plaines home, vibration fatigue is the likely contributor alongside whatever settlement has occurred.
We restored mortar joint continuity on a 1962 bi-level with clay soil settlement near Oakton Street, including crack repair, repointing of the exposed foundation course, and drainage recommendations.
Gurnee: Newer Construction and Settling Corners
Gurnee surprises homeowners because the housing stock is newer - median build date around 1992 - yet stair-step cracking is common. Homes built during rapid development in the 1990s sit on fill soil that continues to compact under load. The settling manifests as stair-step cracks in brick walls, mortar separation at corners, and in some cases visible gaps between the foundation and the first course of brick. These are the signatures of young soil compaction, not historic foundation failure.
Corner separation is the most common visible sign on Gurnee colonials. The two walls of a corner move slightly relative to each other as the footings beneath settle at different rates. The crack traces the mortar joint at the corner in a step pattern moving upward. Monitoring the rate of change over two seasons tells you whether the settling has stabilized.
Foundation Walls and the Above-Grade Transition
The most structurally significant location for stair-step cracking is on the foundation wall or at the transition between the foundation masonry and the above-grade brick. On older Chicago-area homes with brick or block foundation walls, look for stair-step cracking on the interior of the basement as well as the exterior. Interior cracks are sometimes more visible and often show the full extent of movement that the exterior face has partially concealed with previous patch repairs.
For homes with significant foundation cracking - where crack width is substantial or where bowing is visible - the question moves from masonry repair into foundation engineering. See our companion post on Brick Foundation Repair in Older Chicago Homes for the specific considerations around older masonry foundations in this region. Also relevant: Water in the Basement from Masonry covers the moisture consequences of foundation joint failure.
Lincolnwood Two-Flats: Settlement at the Addition Joint
Lincolnwood’s housing stock is a direct mix of Chicago-style two-flats alongside post-war ranch homes, with a median build date of 1955. The two-flats built with soft common brick and lime mortar represent the older half of that range, and they produce stair-step crack patterns that single-family homes rarely match. Multi-unit buildings carry more vertical load on the masonry walls, and differential settlement between a main block and a rear addition is a standard problem on buildings of this age.
Look at the rear corners of the main block where the building transitions to a rear addition. This is where differential settlement concentrates - a step in the foundation footing depth at this joint, or a difference in foundation type between the main block and the addition, makes this the point where movement shows up first. The mortar specification for Lincolnwood pre-1945 two-flats is Type N lime-based; the common error we find is a Portland cement repoint from the 1980s that is now damaging the soft brick at the joint edges.
On two-flats generally, stair-step cracks at the upper corners of window openings are also common. Lintels that span window openings carry the load of the masonry above. When a lintel corrodes or when the masonry above is inadequately supported, the courses above the window spread slightly outward, producing a stair-step crack from the upper corner of the opening. See Lintel Repair: Steel and Stone Above Windows and Doors for the full repair scope.
Front Stoops and Entry Steps
Brick stoops and entry stairs are among the most movement-prone masonry elements on a house. They sit on shallow footings, they are exposed on three or four sides, and they lack a basement to buffer soil temperature changes. Stair-step cracking on brick stoops is extremely common and is usually more cosmetic than structural. The stoop is not a load-bearing element for the building. Monitoring for actual displacement, for cracks wide enough to trap water and accelerate freeze-thaw damage, and for settlement that has tilted the stoop toward the house rather than away from it tells you whether intervention is needed.
Rear Additions
Many Chicagoland houses from the 1920s and 1930s had additions built a generation after the original structure, often on shallower footings or on soil disturbed by the original construction. Differential settlement between the main structure and the addition is predictable, and the crack usually appears at the joint between the two buildings. If you see a stair-step crack running along a line on the exterior that corresponds roughly to where an addition begins, look for a vertical control joint inside that matches. Some builders anticipated the movement; others did not, and the movement has opened a crack of its own.
How Wide Is Too Wide and How to Monitor
Width is the first thing most homeowners want to know, and it is useful but not the complete picture.
A hairline crack, 1/32 inch or less, is not visually significant and is common in older masonry. The mortar has fractured slightly, but no material is missing and no water is traveling through the joint.
A crack in the range of 1/16 to 1/8 inch is worth noting and monitoring. Mark both ends of the crack and both sides of the widest point with a pencil mark and a date. Photograph it at the same angle and light conditions. Come back in six months and in twelve months and compare. If it has not changed, it is likely stable and the repair is a repointing job.
At 1/8 to 1/4 inch, closer attention is warranted. This is wide enough to allow water into the joint, which accelerates freeze-thaw damage and can cause mortar to spall out over time, widening the crack further. A stable crack in this range should be repointed. A growing crack in this range needs professional assessment.
Above 1/4 inch, consult a masonry professional or structural engineer, especially if the crack is on a foundation wall, on a structural bearing wall, or if any displacement is visible. Displacement means the two sides of the crack are at different planes: one side has moved forward or backward relative to the other. That is a structural concern.
The simplest monitoring method: press a slip of paper or a matchstick into the crack and tape both sides with a dated strip. If the paper tears or the matchstick breaks over a few weeks, the crack is active. A more precise method is to apply a small patch of plaster across the crack - if the plaster cracks, the wall moved.
For guidance on reading all crack types a masonry wall can produce, see How to Read Cracks in a Brick Wall.
Repair Approaches: From Repointing to Underpinning
The appropriate repair depends entirely on whether the crack is stable, what caused it, and where it is. There is no single answer.
Repointing Stable Cracks
If monitoring confirms that a crack has been stable for two or more years and the cause is normal differential settlement that has completed, the repair is repointing the affected mortar joints. Old mortar is removed to a depth of at least 3/4 inch per BIA Technical Note 7B, then new mortar is applied in lifts matched to the color and composition of the existing mortar.
On pre-1920 homes, this means using Type N or Type O mortar, or a lime putty mix, to match the historic material. NPS Preservation Brief 2 is explicit: mortar must be softer than the masonry units it contacts, and pre-1920 soft brick requires nothing harder than Type N. On post-war construction, standard Type S (minimum compressive strength 1,800 PSI) is often appropriate for foundation work, and Type N above grade.
The mortar match is not just about appearance. A repointing mortar harder than the original creates a rigid patch in a wall that still moves seasonally. That patch fails at its edges as the surrounding original mortar flexes and the patch does not.
For more on mortar types and why the specification matters, see Type N vs. Type S Mortar and Lime vs. Portland Cement Mortar.
Addressing Active Settlement
If a crack is growing, or if it is accompanied by interior symptoms like doors that no longer close correctly or new cracks in plaster, the cause needs to be identified before masonry repair is done. Repointing an active crack is a cosmetic repair on a structural problem. The crack will reopen.
In some cases, improved drainage around the foundation stops water accumulation that has been causing ongoing settlement. In other cases, tree roots have been undermining the footing. A structural engineer assesses these situations and recommends whether foundation intervention or drainage work is needed before masonry work proceeds. For walls where bowing accompanies the cracking, see Bowing and Bulging Brick Walls.
Underpinning
For cases where the foundation footing has been undermined and the settlement is structural and ongoing, underpinning may be required. It involves excavating around the footing and extending it to bearing soil, or driving piers to stable substrate. This is not a common recommendation - most stair-step cracking in Chicagoland homes does not require it. The range of responses runs from basic repointing at one end to full structural intervention at the other, and what is appropriate depends on what is actually happening in the foundation soil.
Cosmetic vs. Structural: How to Draw the Line
Probably cosmetic: The crack is less than 1/8 inch wide. It has been stable for several years. It is on a non-load-bearing element like a stoop or garden wall. No interior symptoms accompany it. The crack follows the mortar joint cleanly with no displacement between the two sides.
Needs closer attention: The crack is between 1/8 and 1/4 inch wide. You are not sure how long it has been there or whether it has grown. It is on a foundation wall or a structural exterior wall. Slight displacement is visible on close inspection.
Professional assessment warranted: The crack is wider than 1/4 inch. It has grown visibly in the past year. Interior symptoms accompany it. There is displacement between the two sides. Multiple cracks are appearing in a pattern that suggests a corner or section of the building is moving.
Emergency: Wide cracks with displacement, bulging of the masonry face outward, or cracks accompanied by sagging structural members above the wall are urgent situations requiring immediate professional review. See Emergency Masonry Repair for the escalation criteria.
Most stair-step cracks homeowners call us about are in the first or second category. We assess them in the field, monitor the ones that are ambiguous, and repair the ones that are stable. The third and fourth categories require bringing in a structural engineer, and that is the right call: a masonry contractor’s job is the brick and the mortar, not the soil mechanics under the foundation.
Getting the Assessment and Repair Right
If you have stair-step cracking on your home in Evanston, Waukegan, Highland Park, or anywhere across Chicagoland’s North Shore and northwest suburbs, the starting point is an accurate read of what the crack is doing.
Delta - Masonry and Tuckpointing has been working with the older brick housing stock in this region since 1987. We assess stair-step cracks in the context of the full building: foundation type, soil conditions, previous repairs, and whether interior symptoms are present. We handle repointing of stable cracks, brick repair for areas where freeze-thaw or incompatible mortar has damaged the face, and full masonry repair scopes where the damage extends beyond a few joints.
We work across Lincolnwood, Northbrook, Des Plaines, Gurnee, and the surrounding communities. For a free on-site assessment, call (847) 713-1648 or contact us online.
The crack follows the mortar joint because mortar is the weakest plane in the wall. The wall is telling you exactly where the movement happened.