Why brick faces flake off, and what spalling means for the wall

Brick is porous. Water gets into it, the temperature drops below freezing, and the ice expands. Repeated cycles of water freezing inside saturated brick push the outer layer of the brick off in flakes. A National Institutes of Health technical bulletin describes the mechanism plainly. Recurring water accumulation and freezing in saturated brick, it says, results in the flaking of the outer layer.

Every lost face makes the brick thinner and more open to the next wetting, so spalling does not stay still. It is worth acting on, but it is worth acting on the cause, not only the face.

On older brick around Philadelphia and Delaware County, the usual cause is a repair done with the wrong mortar. Soft, old brick needs a soft, lime-rich mortar. A hard Portland-cement repointing job is harder and less permeable than the brick itself. Moisture that gets into the wall can then only escape through the brick faces. It escapes through the face, and in freezing weather it takes the face with it.

The National Park Service’s repointing brief states that mortar must be softer than the masonry units. It also documents a wall where hard cement mortar left water with nowhere to go. Water pressure eventually popped the surface off the bricks, which is spalling by another name. The Brick Industry Association says the same in trade terms. Stronger repointing mortar, its notes warn, can lead to spalling of the brick face.

This is why the fix for spalling is so often repointing rather than brick replacement. If the joints are why the wall is wet, replacing bricks alone just moves the problem to the next course.

Hard mortar is the usual offender on pre-war brick, but any wall that stays soaked will eventually spall. Before anyone prices a repair, the water source should be found:

• Gutters and downspouts that dump water down the wall instead of away from it.
• A failed chimney crown or cap letting water in at the top of the chimney.
• Soil, mulch or splash-back keeping the base of the wall damp.
• Sprinklers or an air-conditioner drip wetting the same spot daily.
• Paint or a coating sealing water in, which is its own cause below.
• Road or sidewalk salt thrown onto lower courses over a winter.

A mason who quotes spalling repairs without asking where the water comes from is pricing the symptom. Ask them which source they found and what they intend to do about it.

The tempting fix is a waterproof coating. It usually makes things worse. A film-forming sealer or a coat of paint stops water from getting in. It also stops the water already inside the wall from getting out. Brick is naturally breathable. The Masonry Advisory Council notes that in freeze-thaw climates, a coating blocking that breathability can cause surface spalling.

The National Park Service’s cleaning brief reaches the same conclusion. The wrong coating, it warns, or a coating that is not needed, can result in serious damage. Repointing with compatible mortar and fixing the water source are the repairs with a record behind them. Sealing the face is not.

In order, the work is usually: fix the water source, repoint the affected joints, and replace the worst bricks. The Brick Industry Association’s maintenance notes cover exactly this sequence. They explain how to inspect for spalled units and how replacement brick should match the wall.

Badly spalled bricks are replaced, not patched with surface filler. Surface patch compounds on exterior brick rarely survive a full winter in this climate. They also make the eventual replacement messier.

We found no published Philadelphia-specific figure for spalling work. These are national numbers, for sizing the job rather than pricing it.

For replacement work, Homewyse’s January 2026 estimate for a single-brick repair task is about $200–$265. That figure carries the setup for one small visit. A wall needing several bricks costs more per brick, but far less per task. For the repointing around it, Angi’s published range is $400–$2,500 per 100 square feet. Local quotes vary in both directions, and a real price needs somebody looking at your wall.

The fuller picture, with each figure's confidence stated, is in what masonry work costs in Philadelphia and Delco.

A few flaked faces at the base of a wall, with sound joints, can usually wait for a scheduled quote. Three kinds should not wait. One is spalling that goes through the full face of many bricks. Another is any spalling on a chimney, which always means water is getting in at the top. The third is spalling beside a rusted steel lintel at a window or door. A lintel that is rusting and expanding will crack the brick above it. That is a structural repair of a different kind.

If you are unsure which kind you have, that is precisely what photographs are for. Submit them once, and the masons who look at the wall will tell you which kind this is.

Every claim on this page traces to one of these published sources, read and checked before being used:

• NPS Preservation Brief 2, Repointing Mortar Joints in Historic Masonry Buildings
• NPS Preservation Brief 1, Assessing Cleaning and Water-Repellent Treatments
• BIA Technical Notes 46, Maintenance of Brick Masonry
• NIH Office of Research Facilities, The Freeze-Thaw Cycle in Concrete and Brick Assemblies (January 2019)
• Masonry Advisory Council, Why You Should Not Paint Brick
• Homewyse, Cost to Repair Brick (January 2026)
• Angi, How Much Does Brick Repointing Cost