Walk up to almost any pre-1920 brick building in Chicagoland and what you are looking at is Chicago common brick. Pull up to a 1930s Tudor Revival in Highland Park and you are likely looking at clinker brick. Drive through Wilmette and Evanston and you will see face brick from the late 1920s and 1930s on houses where curb appeal was part of the spec. These are not interchangeable materials. Each type was made differently, fires at different temperatures, has a different hardness, and behaves differently under stress. Each type needs a different mortar specification.
Most homeowners have never been told any of this. A previous contractor may have repointed with Type S mortar because that is what was in the truck. If the wall had soft common brick, that is a slow-motion disaster. If it had hard pressed brick, it might have been fine. The brick type is the foundation of every repair decision. We have been working across these material categories since 1987, and the consequences of getting this wrong are visible on homes across the North Shore.
Why Brick Type Changes Everything About Repair
Masonry walls move. They expand and contract with temperature, shift with soil settlement, and absorb and release moisture across dozens of freeze-thaw cycles each winter. The original builders understood this. The wall system is designed so that stress travels through the path of least resistance: the mortar joint. The joint is supposed to be softer than the brick on either side of it. The joint erodes over decades. The brick is protected. Eventually you repoint. This is the expected maintenance cycle.
The problem arrives when a contractor uses mortar harder than the brick. The path of least resistance is no longer the joint. Stress transfers directly into the brick face. The face spalls. Thin flakes break away, then larger chips. Brick spalling is irreversible - replacement is the only remedy, which requires matching the original brick type, which brings you back to the question of what type is in your wall.
ASTM C270 governs mortar composition and sets minimum compressive strengths by type. It does not tell a mason which type to use on a given brick. That decision requires knowing the brick. NPS Preservation Brief 2 by Robert C. Mack and John P. Speweik is the authoritative guidance on historic mortar matching. See Type N vs. Type S Mortar for a focused look at that selection process.
Chicago Common Brick: The City’s Workhorse
Chicago common brick is the material that built this city. From the post-fire reconstruction of the 1870s through the bungalow construction wave of the 1910s and 1920s, common brick was the standard unit. It is sometimes called building brick or utility brick: structural function, not visual performance.
Common brick in the Chicago market came primarily from local clay pits along the Illinois and Chicago River corridors. The clay was relatively soft, firing temperatures were lower than modern production, and the result was a brick with comparatively low density. Surface texture was rough and varied. Dimensions were not held to tight tolerances. Color ranged from buff and cream to red and brown depending on clay source and kiln position.
The BIA Technical Note 3A on brick material properties documents the compressive strength range for this class of brick. The key characteristic for repair: this brick is soft. The lime mortar used on original Chicago common brick construction had a minimum compressive strength consistent with Type O (350 PSI minimum per ASTM C270). When Type S Portland cement mortar at 1,800 PSI minimum gets introduced into this system - as many 1970s through 1990s repointing jobs did - the differential reverses. Stress has nowhere to go except into the brick face.
A telling sign of incompatible past repointing: brick spalling precisely at joint edges, following the joint lines. This is not weather damage. It is the result of mortar harder than the brick it joined.
Evanston has the highest concentration of this failure pattern on the North Shore. The city’s oldest residential stock dates to the 1890s, and its greystones along the major corridors are soft common brick on the sides and rear with Indiana limestone facing on the front. Prior Portland cement repairs are documented as the leading cause of brick failure on these structures. See the Chicago bungalow masonry care guide for the broader bungalow-era context.
Face Brick: When Appearance Became the Specification
Face brick started appearing on Chicagoland residential construction in volume from the mid-1920s onward. As the housing market matured, exterior finish quality became a selling point. Face brick is manufactured to be visible: controlled firing temperatures, tighter clay mixes, more consistent dimensions, and a surface designed to be seen. Compressive strength is higher than soft common brick. Absorption rate is lower.
The BIA Technical Note 9A on brick specifications and classification covers the grading and appearance criteria that distinguish face brick from building brick in the production standards. Face brick houses from the 1930s through the 1950s are prevalent across the North Shore in Wilmette, Winnetka, and Kenilworth. BIA Technical Note 8 identifies Type N mortar - minimum 750 PSI per ASTM C270 - as the standard above-grade residential repointing specification for this class of brick. Type S at 1,800 PSI minimum is reserved for below-grade work and high lateral-load applications.
Joint profile matching matters on face brick work. Original construction often specified a particular recessed or flush finish, and changing the profile changes how the wall sheds water. For more on joint profiles, see understanding tuckpointing: the complete guide for Illinois homeowners.
In Wilmette, where the median home dates to 1948 and the primary era runs from the 1920s through the 1950s, face brick predominates on single-family homes. The high water table and lake-proximity humidity drive moisture through any joint that is not sealed correctly - a problem that face brick handles better than soft common brick, but that still requires correct mortar specification and proper joint depth on any repointing.
Pressed Brick: Machine-Made Precision
Pressed brick, sometimes called repressed or dry-pressed brick, was a late-19th and early-20th century product. Clay was pressed under high mechanical pressure into molds with much lower moisture content than typical brick mixes. The resulting unit was denser and more dimensionally precise than common brick, with sharper corners and smoother faces.
Pressed brick was used heavily in commercial and institutional construction from the 1880s through the 1920s. It appears on older residential construction in Chicagoland where a builder wanted a more refined appearance. The late-19th century mansion rows in Evanston and some of the older apartment buildings on the North Shore have pressed brick that is still in excellent condition because the material itself is dense and durable.
The key characteristic for repair purposes: pressed brick is harder than pre-1920 common brick but was still laid in lime-based mortar because Portland cement was not yet the dominant binder. Type O mortar - minimum 350 PSI per ASTM C270 - against brick that might test at 3,000 PSI or higher represents the largest hardness differential you find in Chicagoland masonry.
Repointing pressed brick with modern Portland cement mortar is less immediately catastrophic than on soft common brick, but it still violates the design logic of the original wall system. Cracking at joint edges - tight, straight hairline fractures tracing the mortar lines - is the signature failure pattern on pressed brick that has received an incompatible repointing. The correct specification is a lime-rich mortar: BIA Technical Note 8B on mortar selection supports Type O or a lime putty mix on pressed brick from this era. The joint will need attention again in 20 to 30 years. That is the design. The alternative is brick face damage that no mortar can reverse.
For replacement work on pressed brick, salvage sourcing is the reliable path. See Salvage Brick: Why Old Brick Matters.
Kenilworth: Custom-Fired Estate Brick and Ornamental Stone
Kenilworth sits at its own level in the North Shore brick hierarchy. The village was designed as a planned community in 1889, and the estates built from the 1900s through the 1940s used brick that was not pulled from a regional supplier’s standard run. These were custom-fired units, produced to specific color, texture, and hardness targets for individual estate commissions, typically accompanied by ornamental limestone accents at sills, lintels, and carved facade elements.
The median Kenilworth home was built in 1929 - nearly a century of direct Lake Michigan exposure on material that cannot be matched from any modern production plant. Mortar matching on these homes requires sample analysis of aggregate type, grain size, and pigment. A color chip comparison does not get close enough. Estates here often have three to five chimneys, each potentially in different mortar condition depending on orientation. Using bag mortar on a Kenilworth facade produces a visible mismatch within a season or two.
The ornamental limestone that accompanies the custom brick is a separate repair problem. Limestone sills and lintels delaminate through a different mechanism than brick weathering, and the mortar at stone-to-brick joints requires a different formulation than the brick-to-brick joints elsewhere on the same facade. For more on estate limestone work across the North Shore, see Lake Forest Limestone Estate Restoration.
Evanston Greystones: Two Materials, Two Mortar Systems
Evanston has the oldest residential masonry stock on Chicago’s North Shore, with median construction from 1939 and a significant share of homes dating to the 1890s and 1900s. Its greystones require a contractor to hold two repair systems in mind at once.
A greystone uses Indiana limestone facing on the front facade and soft common brick on the sides and rear. The limestone and brick are different materials that deteriorate through different mechanisms and require different mortar formulations. Joints between limestone blocks need softer mixes - often NHL hydraulic lime - to avoid trapping moisture inside the stone and causing delamination. The common brick sides, given their age, need lime-based mortar appropriate for pre-Portland construction.
Contractors competent at standard brick tuckpointing frequently treat both surfaces with the same mix when working an Evanston greystone. The result looks complete. On the limestone, it means progressive joint failure and eventual stone face deterioration. On the brick sides of a pre-1920 building, a Portland-heavy mortar reverses the mortar-to-brick hardness relationship and starts the spalling clock.
For service area details on Evanston and the specifics of multi-unit greystone work in the city, see the dedicated page.
Clinker Brick: The Over-Fired Outlier
Clinker brick is what you get when brick spends too long in the kiln. The clay over-fires, gases escape from the material, and the faces warp and bulge. The color darkens to deep browns and near-blacks with mottled combinations. The resulting unit is irregular, rough, and visually striking in a way that modern production deliberately avoids.
In the pre-industrial kiln era, clinker brick was spoilage - discarded or sold cheaply. By the 1910s and 1920s, Arts and Crafts and Tudor Revival architects started specifying it on purpose. The irregular surface and mottled color fit the aesthetic they wanted: natural, handcrafted, deliberately imperfect. Tudor Revival homes across Highland Park, Lake Forest, Glencoe, and Evanston use clinker brick as a design element. The dark, rough-textured brickwork is part of the character of these houses.
From a repair standpoint: clinker brick is extremely hard. Over-firing vitrifies the clay, reducing porosity and increasing density. The ASTM C67 test methods for brick absorption and freeze-thaw durability reflect this directly - vitrified brick scores at the high end of durability. But the irregular surface and variable dimensions mean repointing requires careful attention to joint profiles. The original mortar was typically a lime-Portland blend with colored aggregate to match the dark brick. Applying standard gray Portland cement to a clinker brick facade looks wrong immediately.
The starting specification for clinker brick is Type N mortar colored and textured to match the original per BIA Technical Note 8. The appearance matching, not the structural specification, is typically the hardest part of the job.
See Tuckpointing vs. Brick Replacement for when damaged clinker brick requires replacement versus repointing alone.
Modern Extruded Brick
Modern extruded brick - also called wire-cut brick - has been the dominant production method in the United States since the mid-20th century. The clay is extruded through a die and cut by wires into individual units. This produces consistent dimensions, a predictable compressive strength, and the characteristic wire-cut surface texture. Post-1950s residential construction and nearly all commercial construction uses this type.
For above-grade residential repointing, Type N mortar is the standard specification on modern extruded brick. The brick is dense enough that the mortar is well below the hardness threshold. Joint removal depth still matters: BIA Technical Note 7B requires 3/4-inch minimum removal, and that rule applies to modern brick just as it does to historic material. Repointing over a shallow scrape creates bond failure within a few seasons regardless of brick type. See what happens during a tuckpointing job for what proper joint preparation looks like in practice.
Hardness and Mortar: The Pairing Logic
The underlying rule is consistent across all brick types: mortar must be softer than the brick it joins. NPS Preservation Brief 2 is the authoritative source on this for historic masonry. ASTM C270 provides composition and minimum compressive strength standards by type.
Soft pre-1920 Chicago common brick: Type O (minimum 350 PSI) or lime putty. Type N (minimum 750 PSI) is the upper limit. Never Type S or Type M.
Face brick from the 1920s to 1950s: Type N for above-grade residential. Type S (minimum 1,800 PSI) for below-grade or high lateral-load applications.
Pressed brick: treat like soft historic brick regardless of the brick’s own hardness. Type O or Type N, lime-rich.
Clinker brick: Type N with color and texture matching. The challenge is appearance, not structural compatibility.
Modern extruded brick: Type N above grade. Type S where structurally required.
For a side-by-side on Type N and Type S across applications, see Type N vs. Type S Mortar.
How to Identify What Your Home Has
Age of construction is your first data point. Pre-1920 construction in Chicago and the northern suburbs almost always means soft common brick. Between roughly 1920 and 1940, you may have common brick, face brick, or on Tudor Revival and Arts and Crafts houses, clinker brick. Post-1940 construction is predominantly face brick or early extruded production. Post-1960 is overwhelmingly modern extruded brick.
Look at the surface texture. Soft common brick has a rough, varied, slightly irregular surface. Colors shift across the wall. Face brick has a cleaner, more consistent surface. Clinker brick is recognizable by its warped, dark, mottled appearance. Modern extruded brick shows the characteristic wire-cut texture.
The critical test is mortar-to-brick hardness comparison. Run a steel tool along the joint, then try to scratch the brick face. If the mortar scratches easier than the brick, the system is in the right relationship. If the mortar is harder than the brick, there is a compatibility problem and existing or future spalling will follow.
For a professional assessment on any home where you are uncertain, a masonry contractor experienced with historic construction can confirm brick type, mortar specification, and the scope of any existing damage before any work begins. See how to choose the right masonry contractor in Illinois for what to look for.
Why Matching Brick Matters for Replacement
When individual bricks need replacement, the replacement unit has to match the original as closely as possible. A replacement brick with significantly different hardness, absorption rate, or thermal expansion characteristics will behave differently from the surrounding wall, creating stress concentrations at the boundary between old and new material.
Soft Chicago common brick from the 1910s is not being produced by any modern manufacturer. The dimensional profile, the clay body, and the color range of original material cannot be replicated by a production plant. The only reliable source is salvage brick from demolition projects in Chicago and the surrounding area. For brick replacement on any historic or mid-century home, the sourcing question is part of the initial assessment.
See Brick Replacement vs. Tuckpointing to understand when replacement is necessary and when repointing alone is the right scope.
Scheduling an Assessment
If you are uncertain about the brick type in your wall - or if you have seen previous repointing that does not match the original material, or spalling at joint edges on a pre-1940 home - the right first step is a professional assessment that identifies what you have before any work begins.
Delta - Masonry and Tuckpointing works with the full range of brick types found across Chicagoland’s North Shore and northwest suburbs. We carry lime-compatible mortars and maintain salvage brick sourcing relationships for matching on older homes. We work with brick repair and historic restoration specifications on common brick, face brick, pressed brick, and clinker brick construction.
We serve homeowners in Evanston, Wilmette, Highland Park, Lake Forest, Winnetka, and throughout the North Shore and northwest suburbs. Call (847) 713-1648 to schedule an assessment, or contact us online.
The mortar must be softer than the brick it joins. Get that backwards and the wall tells you - one spalled face at a time.