Brick spalling is one of the most misunderstood masonry problems in the Chicagoland area. When the face of a brick cracks, flakes, or pops off, homeowners often assume the brick itself was defective. In most cases, the brick was fine. Water, wrong mortar, or deferred maintenance created the conditions for the brick to fail. Understanding what causes spalling is the first step toward preventing it and avoiding thousands in repair costs.
What Is Brick Spalling?
Spalling is the deterioration of a brick’s surface layer. It ranges from minor surface flaking, where thin layers peel away, to deep fracturing where large chunks of the brick face break off, exposing the softer interior core. Once the hard-fired outer surface is compromised, deterioration accelerates because the porous inner brick absorbs water at a much higher rate than the original fired surface.
The term comes from the German word “spalten,” meaning to split. In masonry, it describes any surface failure where the face of the brick separates from the body. Mild spalling is cosmetic. Severe spalling is structural: it weakens the wall, allows increased water infiltration, and if deferred long enough, can compromise the load-bearing capacity of the masonry.
The Science: Freeze-Thaw and Hydraulic Pressure
The primary mechanism behind what causes brick spalling in Illinois is freeze-thaw cycling. Understanding the physics explains why certain walls fail while others on the same house remain intact.
How Water Destroys Brick From the Inside
All brick is porous to some degree. Modern fired brick typically absorbs between 5% and 12% of its weight in water, measured by the ASTM C67 Initial Rate of Absorption test. When water enters brick through cracks, failed mortar joints, or the brick surface itself, it fills microscopic pore networks within the clay body.
When temperature drops below 32 degrees F, that water begins to freeze. Water expands approximately 9% in volume when it becomes ice. In confined pore spaces, this expansion generates hydraulic pressure that can exceed 2,000 PSI, far more than the tensile strength of most brick - typically 200 to 500 PSI per BIA Technical Note 3A.
The first freeze cycle may cause invisible micro-cracking. The second cycle pushes those cracks slightly wider. Each subsequent cycle admits more water and expands the damage zone. After 5 to 10 winter seasons of this progression, the surface layer separates from the body and visible spalling appears.
Why Illinois Is Especially Destructive
The Chicagoland area sits in one of the highest freeze-thaw frequency zones in the continental U.S. per GLISA climate analysis. Each cycle is a small stress event. Homes on the North Shore - Winnetka, Glencoe, Wilmette - face additional moisture load from Lake Michigan, compounding the cycle count with higher saturation levels. East-facing Winnetka walls take the brunt of lake-effect moisture driven by northeast winds; these walls can experience mortar joint erosion two to three times faster than protected south or west exposures on the same house.
North-facing and east-facing walls are the most vulnerable because they receive less direct sunlight, stay wetter longer, and experience more freeze events than south-facing walls that warm and dry faster.
The Wrong Mortar Problem
After freeze-thaw, the second most common cause of brick spalling is incorrect mortar selection during previous tuckpointing or repair work. This is a problem we encounter on a significant share of the homes we inspect across the North Shore and northwest suburbs.
How Mortar Causes Brick to Fail
Mortar is engineered to be a sacrificial element in a masonry wall. It is supposed to be softer than the brick it surrounds. When thermal expansion, moisture cycling, or minor settlement creates stress in the wall, the mortar absorbs that stress - it cracks instead of the brick.
When a contractor uses mortar that is harder than the brick, the stress equation reverses. The mortar transfers force into the brick, and the brick cracks. This is especially damaging at the mortar-brick interface, where shear forces concentrate. The result is spalling that appears right at the joint line: the brick face pops off in a strip along the mortar joint. BIA Technical Note 3A documents the brick material property thresholds that govern this failure mode.
Type S on Residential Walls: A Common Mistake
Type S mortar (minimum compressive strength of 1,800 PSI per ASTM C270) is designed for below-grade applications, retaining walls, and areas subject to lateral pressure. It is frequently misapplied on above-grade residential walls where Type N at 750 PSI minimum is the correct choice.
The error is understandable but costly. Contractors who primarily do new construction often default to Type S because it sets faster and achieves higher bond strength. On a new wall with new brick, the mismatch may not manifest for years. On a tuckpointing job where the existing brick is already 50 to 100 years old, using Type S mortar can cause visible spalling within 2 to 5 years.
In Northbrook, where the housing stock from the 1960s to 1980s boom used hard machine-pressed brick and builder-grade mortar, the correct approach for tuckpointing is still Type S in most cases - the brick is hard enough to handle it. But on the older soft common brick of Wilmette homes from the 1920s to 1950s, Type S causes exactly the spalling failure mode described above.
Portland Cement on Pre-1920 Homes
Historic homes built before 1920 typically used lime-based mortar with little or no Portland cement. This mortar is intentionally soft, often below 300 PSI. When modern Portland cement mortar, even Type N, is used to repoint these joints, the hardness differential is extreme. The old, soft brick cannot absorb the stress, and spalling follows.
NPS Preservation Brief 2 is the authoritative reference for this issue: lime mortar or a lime-dominant blend formulated to match the original mortar’s hardness and flexibility is required for proper historic restoration on pre-1920 masonry. In Winnetka, where many homes date to the 1920s through 1940s and used soft Chicago common brick with original lime mortar, prior Portland cement repairs by earlier contractors are one of the most consistent causes of the spalling we repair today.
How to Identify Brick Spalling Early
Catching spalling early is the difference between a targeted brick repair and a full wall rebuild.
Stage 1: Surface Crazing (Earliest Sign)
Fine, hairline cracks on the brick face in a network or web pattern. The cracks do not penetrate deeply. The brick surface still feels solid. This stage is often mistaken for normal aging. In Illinois, it is a warning sign that moisture is cycling through the brick and freeze-thaw damage is beginning.
Stage 2: Flaking and Peeling
Thin layers of the brick face begin to separate. You may notice small flakes of brick on the ground below the wall, especially in spring after the winter freeze-thaw season. The brick surface feels rough or uneven compared to neighboring bricks. Color may appear lighter where the fired surface has detached.
Stage 3: Face Popping
Larger pieces of the brick face break away, leaving concave depressions. The exposed interior is softer, lighter in color, and more porous. At this stage, deterioration accelerates because the protective outer surface is gone. Water absorption rates can double or triple.
Stage 4: Deep Fracturing
The brick body cracks through its full depth. Pieces can be pulled away by hand. The structural contribution of the brick is compromised. Adjacent bricks may begin to shift as the wall loses bearing surface. This stage requires brick replacement, not surface repair.
Stage 5: Structural Compromise
Multiple bricks in a localized area have failed. The wall shows visible displacement, bowing, or cracking patterns. Mortar joints around failed bricks have opened, creating water pathways that accelerate damage to neighboring bricks. Rebuilding the affected section is the only repair option.
Prevention Strategies
Preventing brick spalling is far cheaper than repairing it. Most prevention measures are maintenance tasks that must be done consistently.
1. Maintain Mortar Joints
Failed mortar joints are the primary entry point for water. Annual inspection of all mortar joints, especially on exposed elevations, and prompt tuckpointing of deteriorated sections prevents the moisture saturation that drives spalling. BIA Technical Note 7B establishes that joints must be removed to a minimum depth of 3/4 inch before new mortar is applied to achieve adequate bond. Do not wait until the damage is widespread - early intervention costs a fraction of delayed repair.
2. Ensure Proper Drainage
Water pooling at the base of a brick wall saturates the lowest courses. Check that grading slopes away from the foundation, downspouts discharge at least 4 feet from the wall, and no sprinkler heads are hitting the brick directly. In Glencoe, where many homes sit adjacent to ravines that trap moisture and direct water flow against foundation masonry during heavy rain, drainage correction is often the most important single step in spalling prevention.
3. Repair Caps and Crowns
Chimney crowns, wall caps, and coping stones are the first line of defense against water entering the top of a masonry structure. A cracked chimney crown allows water to flow directly into the brick below, causing spalling from the top down. Crown repair or replacement is one of the highest-return masonry maintenance items.
4. Verify Mortar Type Before Any Repair
Before any tuckpointing or repointing work, confirm that the mortar type is appropriate for your brick. A professional contractor will assess the existing brick hardness and select a replacement mortar that is softer than the brick. If you are getting estimates, ask every contractor what mortar type they plan to use and why.
5. Address Flashing and Caulking
Failed flashing at rooflines, window heads, and wall penetrations allows concentrated water flow into the masonry. Inspect flashing at least annually and replace any sections that are lifted, rusted, or separated from the wall.
6. Do Not Apply Film-Forming Sealers Without Expert Advice
Film-forming sealers can trap moisture inside the brick, increasing spalling risk rather than reducing it. Breathable silane or siloxane-based water repellents can help in some situations, but they are not universally appropriate. On historic or very porous brick, sealers can cause more harm than good. Consult a masonry professional before applying any sealer product.
Repair Options for Spalled Brick
When spalling has already occurred, the repair approach depends on the severity and extent of the damage.
Localized Brick Replacement (Stages 2-4)
Individual spalled bricks can be cut out and replaced with matching brick. The key challenge is sourcing period-appropriate brick that matches the size, color, texture, and firing characteristics of the original. For homes in Libertyville, Northbrook, and surrounding communities, we maintain a salvage inventory of vintage Chicago common brick and pressed brick from demolished structures of similar vintage.
Section Rebuild (Stages 4-5)
When spalling has affected a contiguous area, individual replacement becomes impractical. The damaged section is dismantled course by course and rebuilt with matching brick and appropriate mortar. Proper bonding to the remaining wall is critical to maintain structural continuity.
Full Elevation Rebuild
In severe cases where an entire wall face has failed, the wall may need to be taken down to sound material and rebuilt. This is the most expensive outcome and the one that consistent maintenance prevents.
Patching (Limited Use)
Composite patching products exist for filling minor surface defects. They are a cosmetic stopgap, not a structural repair. Patching makes sense on isolated, shallow damage on otherwise sound brick. It is not a substitute for brick replacement when spalling is active and progressive.
The Spalling Problem on Specific North Shore and Lake County Homes
Winnetka and Kenilworth
Homes from the 1920s to 1940s in these communities used soft Chicago common brick laid originally in lime mortar. Prior Portland cement repairs by earlier contractors are the most common cause of spalling we find here. Repairs require lime-dominant mortar matched to the original per NPS Preservation Brief 2, and the correct brick must be sourced before work begins because today’s production brick does not match the color and texture of original 1920s-1930s common brick.
Wilmette
Wilmette’s high water table and lake-proximity humidity push moisture through foundation and lower-wall masonry year-round. Spalling on north-facing facades here is compounded by the combination of chronic moisture and the prior Portland cement repair pattern common on homes from the 1930s to 1950s. Efflorescence on lower courses is usually the visible warning sign that precedes more serious spalling.
Northbrook and Libertyville
These communities built their primary housing stock in the 1960s to 1980s using hard machine-pressed brick. The spalling mechanism here is different: the brick itself is more durable, but builder-grade mortar joints that are now 40 to 60 years old have eroded and are no longer providing an effective water seal. The freeze-thaw damage accumulates through open joints rather than through the brick body itself. Garage wall corners and chimney mortar are the first elements to show failure on this housing vintage.
Related Spalling Posts
If you are seeing spalling appear specifically in spring, the seasonal pattern has its own explanation: Why Brick Spalling Appears in Spring covers why winter damage becomes visible after the thaw. For the broader freeze-thaw picture, see Illinois Weather and Brick Freeze-Thaw Damage.
Take Action Before Another Winter
If you have noticed any signs of brick spalling on your home, waiting through another winter pushes the damage further and repair costs higher. Each freeze-thaw season widens existing cracks and creates new ones.
Delta - Masonry and Tuckpointing has been repairing and preventing brick spalling across Chicagoland since 1987. We assess the condition of your brick, identify the actual cause of the spalling, and provide a written estimate for the correct repair.
Call (847) 713-1648 or contact us online for a free inspection. If you are in Winnetka, Glencoe, Wilmette, Libertyville, or Northbrook, we can typically schedule an estimate within a few days.
Spalling has three causes and only one looks like weather. The other two are contractor errors that took 5 to 15 years to surface.