Why Chicago Brick Spalls: What a Popped Face Is Telling You
By Affordable Tuckpointing Pros, a Chicago tuckpointing and brick repair company in business since 1996. License number MC6337.
Direct answer
Spalling is the face of a brick breaking away from the body of the brick, and in Chicago it is almost always a water story. Water gets into the brick, cannot evaporate back out, and then freezes and expands. NPS describes water wicking into brick cores and, in a northern climate where winter freezes are prevalent, causing the brick to deteriorate from freeze-thaw action. [3] The reason the water cannot get out is usually one of four things: mortar harder than the brick, a coating on the wall, a sandblasted face, or salt crystallising under the surface. [1] [3]
TL;DR
- Spalling is the brick face delaminating or popping off. The brick is the victim, not the cause. The cause is water that got in and could not leave. [3]
- The most common self-inflicted cause is hard mortar. NPS documents a wall where portland-cement mortar less permeable than the soft brick trapped moisture until water pressure popped the surface off the bricks. [1]
- Mortar is supposed to be the sacrificial part. NPS says repointing mortar must be softer and more vapor permeable than the masonry units, so the joint fails before the brick does. [1]
- Salt does it too. NPS says salt crystallisation inside a unit creates pressure that can spall or delaminate the outer surface. That is subflorescence, and it is the dangerous kind. [1]
- Sandblasting is a permanent cause. NPS says blasting removes the outer hard surface of the brick and exposes the softer core, which then takes on water. [3]
- Sealing spalled brick makes it worse. NPS says waterproofing brick with chemicals or non-permeable paint will accelerate the decay by trapping moisture behind the coating, and BIA says not to put film-forming coatings on brickwork in freeze-thaw environments at all. [3] [5]
- Some spalling is a maintenance item and some is an engineering item. BIA puts widespread spalled brick, cracks over 0.075 in. and accumulated rust on lintels in the structural column, which warrants a professional engineer. [2]
One liner: A spalled face is a receipt. Something upstream put water in that brick and kept it there, and replacing the brick without finding it just buys you a repeat.
What is spalling brick?
In short: Spalling is the face of the brick separating from the body of the brick, and it means water got inside the unit and expanded there.
A spalled brick has lost its face. Sometimes it goes as a clean disc that falls off in one piece and leaves a shallow crater. Sometimes it flakes off in thin layers like old paint. Sometimes the corner of a sill or a step just crumbles into sand when you touch it. All three are the same failure: something inside the brick expanded harder than the brick could hold, and the outer skin gave way.
The expansion is nearly always water, in one of two forms. Liquid water that soaks into the brick and then freezes gains volume as it turns to ice, and it does that inside a pore structure that has nowhere to move. NPS puts it directly: water can wick into the brick cores, and in a northern climate where winter freezes are prevalent, it will cause the brick to deteriorate from freeze-thaw action. [3] Or dissolved salt travels into the brick with the water, the water evaporates, and the salt crystallises under the surface. NPS says that salt crystallisation within a masonry unit creates pressure that can cause parts of the outer surface to spall off or delaminate. [1]
Both mechanisms need the same precondition, and it is the part worth your attention: water has to get into the brick and then be unable to get back out. A brick wall that wets and dries freely survives Chicago winters for a century. BIA puts brick in walls at 100 to 150 years and beyond before repairs become necessary. [2] Bricks that spall at year forty are not weak bricks by default. They are usually bricks that were stopped from drying.
That is why the useful question is never “can you replace these bricks.” It is “what is keeping water in this wall.” Replace the brick and leave the cause in place, and you will be looking at the same crater in a few more winters.
Why the freeze-thaw cycle finds every weak brick
In short: Chicago does not need a record cold snap to spall brick. It needs a wet wall and a temperature that crosses freezing, over and over.
Freeze-thaw damage is cumulative and it is driven by the number of crossings, not by the depth of the cold. A wall that sits saturated at 20 degrees all February is doing less damage to itself than a wall that thaws in the afternoon sun and refreezes after dark, every day for a week. Each crossing is a small expansion inside the pore, and each one leaves the pore a little larger and a little more able to hold water for the next one.
That is why spalling shows up in patterns rather than at random, and the pattern tells you where the water is. Look at the bottom three or four courses above grade, where splash-back and snow piles keep brick wet. Look under a sill where a drip edge is missing. Look at a parapet or a chimney above the roofline, where brick is exposed on more than one face and stays wet longer. Look at the north elevation, which gets less sun to drive moisture out. BIA lists sills, parapets, chimneys and copings as the elements that see more severe exposures and may need repairs at shorter intervals than the field of the wall. [2]
The other half of the pattern is the brick itself. BIA says durability depends on achieving incipient fusion and partial vitrification during firing, which is the technical way of saying that how hard a brick was fired decides how much water it will take on. [4] In the same clay and the same process, darker colours go with higher firing temperatures and lower absorption. [4] On an older Chicago building you often have both in the same wall: harder face brick on the street elevation and softer common brick on the sides and the back, sometimes salvaged, sometimes underfired to begin with. The soft ones spall first, and that is not a defect in the repair. It is the wall telling you which units were always going to be the weak link.
None of this is fixable by making the brick tougher. You cannot re-fire a wall. What you can change is how much water reaches the brick and how easily it leaves, which is why almost every real fix for spalling is a drainage fix, a joint fix or a detail fix rather than a brick fix.
The hard mortar trap: when the last repair caused the spalling
In short: If a wall was repointed with a mortar harder than the brick, the repair itself is the most likely reason the faces are popping now.
This is the cause homeowners almost never suspect and the one that does the most damage in Chicago, because it is created by well-intentioned work. Mortar in a masonry wall is designed to be the weak component. NPS calls the mortar joint the wall’s first line of defence and says plainly that mortar joints are intended to be sacrificial. [1] The joint is supposed to absorb movement, carry moisture out of the wall and wear out on a schedule, so that the brick, which is expensive and irreplaceable, does not.
Modern portland-cement mortar breaks that arrangement. It is stronger and less permeable than a lot of older Chicago brick, and NPS is explicit about the consequence: a mortar stronger in compressive strength than the masonry units will not give, so stresses are relieved through the masonry units instead, resulting in permanent damage such as cracking and spalling that cannot be repaired easily. [1] The moisture path fails the same way. NPS documents a wall where hard portland-cement mortar less permeable than the soft bricks trapped moisture that could not evaporate through the joint, until water pressure eventually popped the surface off the bricks. [1] The same article repeats it for general cases: hard mortars with high concentrations of portland cement are less permeable than the surrounding brick and will often cause the surrounding masonry to deteriorate faster. [3]
So the failure runs in a specific direction. The wall gets repointed, the joints look sharp and sound for several years, and then the brick faces start letting go, often in a band right where the new work was done. The joint is fine. That is the tell. When the mortar looks better than the brick around it, the mortar is the reason.
The rule NPS sets for getting it right is short and it belongs on every quote you read: new mortar must have greater vapor permeability and be softer, measured in compressive strength, than the masonry units, and it must be as soft or softer than the historic mortar already in the wall. [1] BIA translates that into a specification you can ask for by name, recommending prehydrated Type N, O or K mortar for repointing. [2] If a contractor quotes you Type S or Type M on an older soft-brick Chicago building and cannot explain why, that is the conversation to have before the work starts, not after. Our post on tuckpointing versus repointing covers how to get the mix written into the scope.
Undoing it is the unhappy part. Hard mortar in the joints cannot be softened. It has to be cut out and replaced with a compatible mix, which is the full cost of the repointing job again, on top of replacing whatever brick was lost in the meantime.
Sandblasting: the cause you cannot reverse
In short: Abrasive cleaning strips the hard fired skin off the brick and leaves the soft core open to water, permanently.
A brick is not uniform. The outer surface is denser and harder than the inside, because that is the part that took the heat and the pressure during manufacture. BIA describes the smooth die skin formed by the steel die as the clay passes through it in extrusion. [4] Firing then hardens the exterior further. That skin is the brick’s weather protection, and it is a few millimetres thick.
Abrasive cleaning removes it. NPS is blunt about the sequence: the blasting operation causes the loss of the outer hard surface of the brick, exposing the softer core, and once exposed, water penetrates more easily, which makes the brick vulnerable to freeze-thaw deterioration. [3] BIA lists previous sandblasting among the probable causes to consider when you observe spalled units on a wall. [2] Acid cleaning done badly does a related kind of harm. BIA notes that improper cleaning, including insufficient prewetting, insufficient rinsing and strong chemical concentrations, can etch mortar joints and increase moisture penetration in brickwork. [2]
Chicago has a lot of this. Sandblasting brick was common through the 1960s and 1970s and the results are still standing. A blasted elevation often reads as unusually matte and slightly rough compared with an unblasted one, with the arrises of the bricks softened and the mortar joints cut back below the brick face. If your building was cleaned that way at some point, the spalling you are seeing now may have been set in motion decades before you owned it.
There is no repair that puts the skin back. NPS notes that even modern water-repellent products are not consolidants and that the composition of fired products such as brick does not lend itself to consolidation. [6] What is left is managing water: keeping joints sound, keeping drainage away from the wall, and replacing individual units as they fail. It is maintenance rather than cure, and a contractor who tells you otherwise about a blasted wall is selling you something.
Efflorescence, subflorescence and which one you should worry about
In short: The white powder on the outside of the wall is mostly harmless. The salt you cannot see, crystallising just under the brick face, is what spalls it.
Efflorescence is the white bloom that appears on brick, usually after a wet spell. BIA describes it as white deposits left on the brick surface when moisture carrying dissolved salts evaporates. [2] It is unattractive and it washes or brushes off, and on its own it does very little damage.
What it is actually reporting is more useful than what it looks like. Salt does not appear on a dry wall. Efflorescence means water is moving through the masonry, picking up soluble salts from the brick or the mortar, and carrying them to the surface. BIA’s instruction is to scrutinise masonry with persistent efflorescence for unresolved water penetration issues, and to investigate and resolve the water ingress before cleaning, because otherwise the efflorescence will simply come back. [2] Treat it as a gauge, not a stain.
The dangerous version is the one that never reaches the surface. If the salt crystallises inside the brick instead of on it, that is subflorescence, and NPS says it may eventually cause the surface of the masonry to spall. [6] The mechanism is the same pressure story as ice: crystals growing in a confined pore push outward until the face lets go.
This is where sealing a wall becomes actively harmful rather than merely useless. NPS says subflorescence is particularly likely to spall the surface where a water-repellent coating has been applied, because the coating reduces the flow of moisture out from the subsurface of the masonry, and that coatings can be especially damaging on masonry that contains salts because they limit the flow of moisture through it. [6] A wall showing efflorescence is a wall carrying salt. Putting a coating on it traps the salt where it does damage instead of letting it bloom harmlessly on the face.
Why sealing spalled brick makes the spalling worse
In short: A coating does not stop the water that is already getting in, and it does stop that water from leaving.
The instinct when brick starts crumbling is to seal it. It is the wrong move on a Chicago wall, and both authorities say so in unusually direct language. NPS states that waterproofing the brick either with chemicals sold for that purpose or by painting with non-permeable paint or other coatings will accelerate the decay by trapping moisture behind the new coating. [3] BIA’s recommendation for clear coatings includes a line that applies to every building in this city: do not apply film-forming coatings to brickwork located in freeze-thaw environments. [5]
The reason is that the coating is on the wrong side of the problem. Water rarely enters brickwork through the face of a sound brick. BIA says water usually penetrates at separations and cracks between brick and mortar or at junctures with other materials, and that penetrating water-repellent coatings seldom stop water penetration through cracks more than 0.02 in. wide. [5] So the coating fails to close the actual entry route, while it does reduce the wall’s ability to dry. On a spalling wall, drying is the only thing keeping the damage from accelerating.
BIA’s sequencing instruction is the one to follow: before considering application of external coatings, inspect the masonry and correct all deficiencies. [2] Correct the conditions contributing to water penetration before applying anything. [5] In practice on a spalling Chicago building that means repointing with a compatible mortar, fixing sills and copings that have lost their slope or their drip, clearing gutters and downspouts so water is not running down the wall, and replacing the units that are past saving. Do that and the wall usually does not need a coating. NPS says as much: if masonry buildings are kept watertight and in good repair, water-repellent coatings should not be necessary. [6]
When spalling is maintenance and when it is structural
In short: Scattered spalled faces are a repair item. Widespread spalling, wide cracks or rusting lintels are an engineering item, and BIA draws that line explicitly.
Not all spalling carries the same urgency, and BIA gives a usable threshold rather than a judgement call. It lists conditions that indicate structural issues and warrant investigation by a professional engineer: cracks in brick masonry exceeding 0.075 in. in width, cracks through multiple brick units, cracks following a stepped or diagonal pattern, widespread spalled brick, accumulated rust on lintels or shelf angles, out-of-plane movement of brick masonry or other wall elements, and neutral or negative slope on masonry sills and water tables. [2]
Read that list as a screening tool. A dozen spalled faces scattered across an elevation, with tight mortar and no cracking, is maintenance. The same elevation with a stair-step crack running through the bricks rather than around them, or with a wall that is visibly bowing, or with rust staining and lifted brick over the windows, is a different conversation and it starts with an engineer rather than a mason. Rust on a lintel in particular is on BIA’s structural list because the steel expands as it corrodes and lifts the masonry it is carrying.
The inspection habit that catches all of this early is seasonal. BIA recommends performing periodic inspections, preferably each season, so that the behaviour of the materials in various weather conditions can be observed, and suggests using binoculars and adjacent roofs or balconies to get a close view of upper floors. [2] For a Chicago building the highest-value look is the one in early spring, right after the freeze-thaw season has finished doing its work and before the summer hides it.
What you are looking for is on BIA’s own checklist: cracked units, loose units, spalled units, hairline cracks in mortar, deteriorated mortar joints, missing or clogged weeps, efflorescence, stains, inadequate slope on caps, copings and sills, and damaged or missing flashing. [2] Any one of those is a water route, and water routes are what produce spalled brick two or three winters later.
What replacing a spalled brick actually involves
In short: The unit is cut out without damaging its neighbours, a matched replacement is set, and the joints around it are pointed, which is why matching is the hard part.
Brick replacement is careful demolition before it is anything else. BIA’s method is to break the damaged brick to assist with removal, then cut and remove the remaining mortar without damage to adjacent units, then butter the surfaces of the new brick and the surrounding brick and point the joints around the new unit after installation. [2] The reason for breaking the unit first is that trying to lever a whole brick out puts force into the bricks beside it, and a replacement job that creates two new cracked units for every one it fixes is not a repair.
Matching is where these jobs are won or lost, and it is genuinely difficult on older Chicago stock. Colour in fired clay comes from its chemical composition and the firing temperature and method, so a brick from a different plant or a different decade rarely lands in the same place. [4] BIA’s answer is not to guess: when selecting new brick to match the appearance of existing brick, use mock-ups or sample panels, and do the same when selecting repointing mortar to match the existing joints. [2] On a visible elevation that step is worth insisting on. On buildings where a match is not achievable, salvaged brick from a hidden elevation of the same building, with new brick used in the concealed location, is often the better-looking result.
The pointing around the replacement follows the same compatibility rule as the rest of the wall, and BIA gives the workmanship detail: install repointing mortar in multiple quarter-inch lifts, tooling each when thumbprint hard. [2] That is the difference between a joint that lasts and one that shrinks back and cracks in its first winter.
Expect the scope to be larger than the visible damage. A brick that has spalled has been wet for a long time, and the units and joints around it usually have their own water history even if the faces are still on. Our brick repair and tuckpointing pages cover how the two get scoped together, and what actually drives the price on a Chicago quote.
Spalling brick questions Chicago homeowners ask
What causes brick to spall in Chicago?
Water inside the brick that cannot evaporate back out, then freezes. NPS describes water wicking into brick cores and causing freeze-thaw deterioration in northern climates. [3] The reason it cannot leave is usually mortar harder than the brick, a coating, a sandblasted face, or salt crystallising under the surface. [1] [3]
Is spalling brick a structural problem?
Sometimes. BIA puts widespread spalled brick on its list of conditions that warrant investigation by a professional engineer, along with cracks exceeding 0.075 in., cracks through multiple units, stepped or diagonal cracking, accumulated rust on lintels or shelf angles, and out-of-plane movement. [2] Scattered spalled faces with sound joints and no cracking are a maintenance item.
Can you repair a spalled brick or does it have to be replaced?
Replaced. The lost face is gone and cannot be rebuilt. BIA’s procedure is to break the damaged unit to assist removal, cut out the remaining mortar without damaging adjacent units, set a matched replacement, and point the joints around it. [2]
Should I seal my brick to stop it spalling?
No. NPS says waterproofing brick with chemicals or non-permeable coatings will accelerate the decay by trapping moisture behind the coating, and BIA says not to apply film-forming coatings to brickwork in freeze-thaw environments. [3] [5] Correct the water source first. [2]
Why did my brick start spalling after it was tuckpointed?
Almost certainly the mortar was too hard. NPS documents portland-cement mortar less permeable than the brick trapping moisture until water pressure popped the surface off the bricks, and says a mortar stronger than the units relieves stress through the units instead, causing cracking and spalling. [1] New mortar must be softer and more vapor permeable than the brick. [1]
Does sandblasting cause spalling?
Yes, and permanently. NPS says blasting removes the outer hard surface of the brick and exposes the softer core, after which water penetrates more easily and the brick becomes vulnerable to freeze-thaw. [3] BIA lists previous sandblasting as a probable cause of spalled units. [2]
Is the white powder on my brick a sign of spalling?
Not directly, but it is a warning. Efflorescence is salt left behind when moisture evaporates, and BIA says persistent efflorescence should be scrutinised for unresolved water penetration. [2] The damaging version is subflorescence, salt crystallising under the surface, which NPS says may eventually spall the face. [6]
How often should I be checking the brick?
BIA recommends periodic inspections, preferably each season, using binoculars and adjacent roofs or balconies for upper floors. [2] In Chicago the early-spring look is the valuable one, right after the freeze-thaw season.
How long should brick last before any of this is normal?
BIA estimates 100 to 150 years and beyond for brick in walls before repairs become necessary, against 50 years and beyond for the mortar. [2] Sills, parapets, chimneys and copings see more severe exposure and may need repairs sooner. [2]
Stats box
| Figure | Value | Source | Date |
|---|---|---|---|
| Estimated time to repair, brick in walls | 100 to 150+ years | BIA Technical Note 46, Table 1 [2] | December 2017 |
| Estimated time to repair, mortar in walls | 50+ years | BIA Technical Note 46, Table 1 [2] | December 2017 |
| Estimated time to repair, water repellents on walls | 5 to 10 years | BIA Technical Note 46, Table 1 [2] | December 2017 |
| Crack width that indicates a structural issue | Over 0.075 in. (2 mm) | BIA Technical Note 46 [2] | December 2017 |
| Crack width a penetrating water repellent will not stop | Over 0.02 in. (0.5 mm) | BIA Technical Note 6A [5] | August 2008 |
| Recommended inspection interval | Each season | BIA Technical Note 46 [2] | December 2017 |
| Repointing mortar lift thickness | Quarter-inch lifts, tooled at thumbprint hard | BIA Technical Note 46 [2] | December 2017 |
Definition bank
| Term | Definition |
|---|---|
| Spalling | The face of a masonry unit breaking, flaking or popping away from its body, driven by pressure inside the unit from freezing water or crystallising salt. [1] [3] |
| Freeze-thaw action | Repeated freezing and thawing of water held inside masonry. NPS names it as the mechanism by which water wicked into brick cores deteriorates brick in northern climates. [3] |
| Sacrificial mortar | Mortar specified softer and more vapor permeable than the brick so the joint wears out first. NPS says mortar joints are intended to be sacrificial. [1] |
| Vapor permeability | How readily a material lets water vapor pass through it. NPS requires repointing mortar to be more vapor permeable than the masonry units. [1] |
| Efflorescence | White salt deposits left on the brick surface when moisture carrying dissolved salts evaporates. Largely cosmetic, but a signal of unresolved water penetration. [2] |
| Subflorescence | Salt crystallising below the surface rather than on it. NPS says it may eventually cause the masonry surface to spall. [6] |
| Die skin | The smooth dense surface formed by pressure from the steel die as clay is extruded, part of what makes the outside of a brick harder than its core. [4] |
| Incipient fusion | The partial vitrification achieved during firing that BIA identifies as what brick durability depends on. [4] |
| Film-forming coating | A coating that leaves a continuous film on the masonry surface. BIA says not to apply these to brickwork in freeze-thaw environments. [5] |
| Structural indicator | A condition BIA says warrants a professional engineer, including widespread spalled brick, cracks over 0.075 in., cracks through multiple units, stepped or diagonal cracking and accumulated rust on lintels or shelf angles. [2] |
Entity cards
Spalled brick
| Property | Value |
|---|---|
| What failed | The face of the unit, not the joint [1] [3] |
| Primary driver | Water held in the brick, then frozen [3] |
| Secondary driver | Salt crystallising below the surface [1] [6] |
| Common upstream cause | Mortar harder and less permeable than the brick [1] [3] |
| Repairable in place | No. The unit is replaced [2] |
| Structural when | Widespread across an elevation [2] |
Freeze-thaw action
| Property | Value |
|---|---|
| What it acts on | Water already absorbed into the brick core [3] |
| Where it shows first | Sills, parapets, chimneys, copings, low courses [2] |
| Made worse by | Anything that slows drying, including coatings [3] [5] |
| Not fixed by | Sealing the face of the wall [3] [5] |
| Fixed by | Removing the water route and restoring drying [2] [5] |
Hard mortar damage
| Property | Value |
|---|---|
| Mechanism, stress | Mortar will not give, so stress relieves through the brick [1] |
| Mechanism, moisture | Moisture cannot evaporate through the joint and pops the face [1] |
| Documented by | NPS Preservation Brief 2 [1] |
| Required property | Softer and more vapor permeable than the units [1] |
| Mortar types named | Prehydrated Type N, O or K [2] |
| Reversible | Only by cutting the mortar out and repointing again [1] [2] |
Abrasive cleaning damage
| Property | Value |
|---|---|
| What is removed | The outer hard surface of the brick [3] |
| What is exposed | The softer core [3] |
| Consequence | Easier water penetration, then freeze-thaw [3] |
| Listed as a cause by | BIA Technical Note 46, Table 3 [2] |
| Reversible | No. Brick does not lend itself to consolidation [6] |
Finding the water before you replace the brick
In short: Ask what is putting water into the wall and what is stopping it leaving, and you have asked the only two questions that decide whether the repair holds.
Spalled brick is the visible end of a process that started somewhere else. In Chicago that somewhere is a short list: joints that have opened, mortar that was specified too hard, a sill or coping that has lost its slope, a downspout putting water down the wall, a coating that stopped the wall drying, or a face that was sandblasted before you owned the building. [1] [2] [3] [5]
A contractor who quotes you brick replacement without naming which of those is happening on your wall is quoting you a repeat job. One who walks the elevation, looks at the joints and the sills and the drainage first, and tells you what mix is going back in, is pricing a repair that lasts. BIA’s own sequence is to inspect the masonry and correct all deficiencies before anything else goes on the wall. [2]
If you want that written down for your building, get a free quote from our team and we will tell you which one it is.
Sources
- National Park Service, Preservation Brief 2, “Repointing Mortar Joints in Historic Masonry Buildings”, Mack and Speweik, rev. 1998. https://www.nps.gov/orgs/1739/upload/preservation-brief-02-repointing.pdf
- Brick Industry Association, Technical Note 46, “Maintenance of Brick Masonry”, December 2017. https://www.gobrick.com/media/file/46-maintenance-of-brick-masonry.pdf
- National Park Service, “Common Problems with Brick Masonry”, Technical Preservation Services. https://www.nps.gov/articles/common-problems-with-brick-masonry.htm
- Brick Industry Association, Technical Note 9, “Manufacturing of Brick”. https://www.gobrick.com/media/file/9-manufacturing-of-brick.pdf
- Brick Industry Association, Technical Note 6A, “Colorless Coatings for Brick Masonry”, August 2008. https://www.gobrick.com/media/file/6a-colorless-coatings-for-brick-masonry.pdf
- National Park Service, Preservation Brief 1, “Assessing Cleaning and Water-Repellent Treatments for Historic Masonry Buildings”, Mack and Grimmer, 2000. https://www.nps.gov/orgs/1739/upload/preservation-brief-01-cleaning-masonry.pdf