Why Is My Brick Flaking? Spalling Explained – Causes and What to Do Before It Spreads

You’ve noticed it on the gangway wall or the chimney: the smooth face of a brick has flaked away, exposing a rough, crumbly orange interior. That’s spalling – and it matters, because a spalled brick can’t be repaired, only replaced. Here’s what causes it, why it spreads, and how to stop it while most of your wall is still intact.

What exactly is brick spalling?

A fired brick isn’t the same material all the way through. The kiln gives it a dense outer skin – the “fire skin” – that sheds water and takes the weather, protecting a softer, more porous core. Spalling is what happens when that skin cracks, flakes, or pops off entirely. Once the core is exposed, it absorbs water like a sponge, freezes, and crumbles a little more every winter. That’s why spalling accelerates: each flake makes the next one easier.

This matters double on Chicago’s pre-1950 buildings, because their common brick – the soft, salmon-pink brick on side and rear walls – was fired unevenly at lower temperatures. Beautiful, but with a thinner skin and a softer core than modern brick. It has less margin for error than almost any masonry material we work with.

What causes spalling on Chicago buildings?

Nearly every case we inspect traces back to one root cause – trapped moisture – arriving through one of these doors:

Hard cement repointing. The most common cause we see. When old lime joints get repointed with Portland cement that’s harder and less breathable than the brick, moisture can no longer escape through the joints – so it exits through the brick face instead, freezing and popping the skin off along the way. The telltale pattern: bricks flaking right next to intact, proud gray joints. We’ve written a full guide to this mechanism in Lime Mortar vs. Portland Cement.
Failed water details up top. Parapets, copings, chimney crowns, and sills with failed drip edges pour water into the wall below. The spalling shows up mid-wall, but the cause is at the roofline.
Waterproofing sealers. Well-meaning owners coat a damp wall with sealer to “protect” it – and seal the moisture inside. A historic wall must breathe; a film-forming coating on soft brick often turns slow damage into fast damage. The National Park Service’s Preservation Brief 1: Assessing Cleaning and Water-Repellent Treatments calls inappropriate cleaning and coating treatments a major cause of damage to historic masonry – and explains when a coating is (rarely) justified.
Sandblasting in the building’s past. Popular decades ago for “cleaning,” sandblasting strips the fire skin off the entire wall at once. If your whole facade is uniformly rough and thirsty, this may be why – and it makes every other cause above hit harder. The NPS considers the danger serious enough that its library of Preservation Briefs devotes an entire brief (No. 6, “Dangers of Abrasive Cleaning to Historic Buildings”) to the subject.
Rising damp and salts. Moisture wicking up from the foundation carries dissolved salts that crystallize inside the brick face and push it apart. Look for white, crusty efflorescence bands low on the wall.

Can a spalled brick be repaired?

Honestly: no. Once the face is gone, no coating or patch restores the fire skin – cosmetic “brick repair” compounds smeared over a spalled face tend to trap moisture and fail. The real fix has two parts: replace the bricks that are past saving (we match salvaged Chicago common brick and vintage face brick so replacements disappear into the wall), and – far more important – remove the cause, or the new brick will spall just like the old one did.

Removing the cause usually means some combination of: taking out hard cement joints and repointing in a softer, breathable lime mix; rebuilding the water details at parapets, copings, and sills; and never, ever sealing or blasting the wall. This is the core of what proper brick mortar repair and masonry restoration actually do – they manage water, not just cosmetics.

How do I know if it’s urgent?

A quick triage you can do from the sidewalk:

A few scattered spalled faces, joints look original and sound – not an emergency. Photograph it, watch it, plan the repair within a season or two.
Spalling concentrated next to hard gray mortar, or below a parapet/chimney – the cause is active and feeding it. Get an assessment before the next winter; every freeze-thaw cycle is taking brick you can’t get back.
Deep spalling, bricks crumbling through, bulging or displaced areas – structural territory. Have it looked at now, not in spring.

Frequently asked questions

Is spalling covered by homeowner’s insurance?

Usually not – policies typically treat it as gradual deterioration or deferred maintenance rather than sudden damage. One more reason catching it early is worth real money: repointing a wall costs a fraction of rebuilding one.

Will painting the wall stop the spalling?

The opposite, usually. Most paints and sealers reduce the wall’s ability to dry outward, and on soft historic brick that traps the moisture that drives spalling. If a coating is ever appropriate, it has to be vapor-permeable and chosen for the specific wall – not a default fix.

The previous owner already repointed with cement. How bad is it?

It depends on how much brick has already been lost. If spalling is just beginning, carefully removing the cement and repointing in a matched lime mortar stops the mechanism, and the wall keeps most of its original brick. The longer the cement stays in, the more replacement brick the job eventually needs.

Why does spalling show up mostly on the side and back walls?

Because that’s where Chicago builders used common brick – softer and more porous than the pressed face brick on the street facade. Same wall, same weather, weaker skin. It’s also where budget “tuckpointing” tends to happen, which is how the most vulnerable brick ends up with the most damaging mortar.

Sources & further reading: National Park Service, Preservation Brief 1 – Assessing Cleaning and Water-Repellent Treatments for Historic Masonry Buildings · National Park Service, Preservation Briefs library (see No. 6 on abrasive cleaning and No. 39 on controlling unwanted moisture in historic buildings)

Seeing flaking brick on your building? Send us a few photos – we’ll tell you honestly whether it’s cosmetic, active, or urgent, and what’s feeding it. Learn more about our brick mortar repair and historic brick restoration services, or get in touch for a free assessment.