Spalling brick is brick whose face has flaked, chipped, or popped off, leaving a rough, crumbly surface and often a pile of red chips on the roof or in the gutter. On a chimney it usually starts near the top, on the side that faces the weather, and spreads downward. The cause is almost always the same: the brick got saturated with water, the water froze and expanded inside the pores, and the outer face broke away. Seattle's climate is built to do exactly that.
The fix depends on how far it has gone. A few spalled bricks near the crown can be cut out and replaced, with the crown and cap fixed so water stops getting in. A chimney where most of the exposed brick has lost its face usually needs the top courses rebuilt. Either way, the first step is stopping the water, because replacing brick without fixing the water source just resets the clock. Here is why Seattle is hard on chimney brick, what spalling looks like, and what we do about it.
Why Seattle weather spalls chimney brick
It is wet for half the year
Sea-Tac's annual rainfall normal is about 40 inches, but the timing matters more than the total. Roughly 73 percent of that rain falls between October and March. November alone averages over six inches. During those months a chimney top rarely dries out. The crown, the top few courses of brick, and the mortar joints sit damp for weeks at a time, and any crack in the crown or open joint pulls water deeper into the masonry.
It freezes and thaws instead of staying frozen
Seattle does not get long hard freezes. Winter low temperatures at Sea-Tac average just above freezing, around 37 degrees in December through February. But the city touches 32 degrees or lower on about 60 days a year while only about 4 days stay below freezing all day. That means the same wet brick can freeze overnight and thaw by lunch, over and over, all winter. Every cycle pushes the brick face out a little more.
Saturated brick plus freezing equals spalling
The Brick Industry Association's technical notes explain the mechanism directly: water in saturated brick pores expands when it freezes, and repeated freeze-thaw of saturated masonry causes cracking, crazing, spalling, and disintegration. The key word is saturated. Dry brick survives freezing fine. Brick that is wet to the core does not. Building science research on clay brick reaches the same conclusion: damage risk is driven by saturation plus freezing, so keeping the masonry dry, not warm, is what protects it.
Moss makes it worse
Western Washington moss grows fastest from October through April and on shaded, north-facing surfaces that dry slowly. A chimney on the shady side of the roof gets the same treatment. Moss holds water against the brick and its root-like rhizoids can lodge in open mortar joints, which keeps the masonry saturated longer and gives freeze-thaw more to work with.
How to recognize spalling on your chimney
You can see most of this from the ground or from a window with a clear view. Do not go on the roof to check; we will do that.
- Flaked or pitted brick faces. The smooth fired surface is gone and the softer inner brick is exposed. Once the face is gone the brick absorbs water even faster.
- Red chips in the gutter or on the roof. Brick fragments collect at the base of the chimney and wash into the gutters.
- White powdery stains (efflorescence). Salts left behind as water moves through the brick and evaporates. A sign the masonry is getting wet from the inside.
- Recessed or missing mortar. Joints that have washed out let water in behind the brick.
- Damage concentrated at the top. The top courses sit under the crown and take the most water. If the crown is cracked, the bricks just below it fail first.
- Damage on one side. The side facing prevailing weather, or the shaded side that never dries, usually goes first.
Where the water is coming from
Spalling is a symptom. Before we replace a single brick we find the entry point, because almost every spalled Seattle chimney has one of these feeding it.
A cracked or flat crown
The crown is the sloped slab on top that sheds water away from the brick. A cracked crown lets water straight into the top courses. A crown poured flat, or without an overhang, drips water down the brick faces instead of away from them. Depending on condition, we either seal it with a flexible coating (crown repair) or remove it and form a new one with proper slope and drip edge (crown rebuild, starting at $299).
A missing or damaged cap
Without a cap, rain falls directly down the flue. The flue tiles and the brick around them stay wet, and the moisture migrates outward. A chimney cap is one of the least expensive parts of the system and one of the most important.
Open mortar joints
The Brick Industry Association notes that improperly filled mortar joints lead to leaky walls and contribute to cracking and disintegration from water penetration followed by freezing and thawing. Joints that have eroded below the brick face hold water like a shelf. Repacking them is part of any spalling repair.
Failed flashing
Flashing problems usually show up as leaks inside the house rather than spalling, but lifted flashing can keep the base of the chimney wet. We check it during the same inspection.
How we repair spalled brick
Stop the water first
Every spalling repair starts at the top. We fix the crown, confirm the cap, and seal or repack joints so the masonry can start drying out. Replacing brick under a cracked crown is wasted money.
Replace individual bricks when the damage is limited
When a handful of bricks have spalled and the rest are sound, we cut out the damaged units, clean the pocket, and set new brick matched as closely as possible in size, color, and absorption. Mortar is mixed to suit the existing brick rather than defaulting to the hardest mix, because mortar that is stronger than the brick pushes stress into the brick and causes more spalling.
Rebuild the top courses when the damage is widespread
If most of the exposed brick above the roofline has lost its face, or the chimney is leaning or separating, replacing bricks one at a time stops making sense. We take the chimney down to sound brick, rebuild the courses, and pour a new crown with a proper overhang. This is the most common form of chimney repair on older Seattle homes, and it is almost always a partial rebuild from the roofline up rather than a full teardown.
Keep it dry afterward
A new crown with overhang and drip edge, a proper cap, and full mortar joints are the three things that keep a repaired chimney from spalling again. We also recommend clearing moss from the roof around the chimney so the brick gets a chance to dry between storms.
Which Seattle homes get this most
Seattle's median home was built in 1976, and about half the city's houses date from before the late 1980s. Pre-1970 homes in Ballard, Wallingford, Greenwood, West Seattle, and Beacon Hill almost all have brick masonry chimneys that have now been through many wet winters. Shoreline and Edmonds, with housing stock from the 1940s through the 1970s, see the same pattern. Tacoma's older Craftsman and bungalow neighborhoods are the same story further south. If your house is from that era and nobody has looked at the chimney top in a few years, it is worth a free quote before the rain returns in October.
What to do next
- Look from the ground or a window for flaked brick faces, red chips in the gutters, or white staining. Do not climb on the roof.
- Stop using the fireplace if brick is falling or the chimney looks like it is leaning, and call us.
- Call 206-453-2045 or request a free quote. We inspect the crown, cap, joints, and flashing, show you photos, and give you a written quote. Same-day service is often available in Seattle, Tacoma, Everett, and across the Puget Sound.
- Already have a quote? Ask for our free second opinion. We price match and take 10 to 25 percent off.
- Plan the repair for the dry season if you can. Summer in Seattle averages only about 3 inches of rain, which is the best window for masonry work and for the chimney to dry out.
We are certified and insured, we use safe and green materials, and if you are not happy, we are not done.
Questions homeowners ask
What is spalling brick?
Spalling is when the face of a brick flakes, chips, or pops off, exposing the softer material underneath. It happens when water soaks into the brick and then freezes and expands. On chimneys it usually starts at the top, on the side that faces the weather or stays shaded.
Why does Seattle weather cause spalling when it rarely gets very cold?
Seattle chimneys stay wet for months, since about 73 percent of the year's rain falls October through March. The city touches freezing on about 60 days a year but only stays frozen all day on about 4, so wet brick freezes and thaws repeatedly. Saturation plus repeated freezing is exactly what breaks brick faces.
Can spalled brick be repaired, or does the chimney need a rebuild?
A few spalled bricks can be cut out and replaced once the crown, cap, and joints are fixed. When most of the brick above the roofline has lost its face, or the chimney is leaning, a partial rebuild of the top courses is the better repair. We tell you which one your chimney needs and why.
Will sealing the brick stop spalling?
Not by itself. The water has to be stopped at the source first: crown, cap, and mortar joints. Sealing brick that is still taking on water from the top can trap moisture and make freeze-thaw damage worse.
Is a spalling chimney dangerous?
Loose brick can fall onto the roof or the ground, and a chimney that has lost a lot of brick can become unstable. If you see brick falling or the chimney looks like it is leaning, stop using the fireplace and call us for a free quote.
Related