How Water Actually Gets Through a Brick Wall — Finding the Leak Before You Pay to Fix It

The short answer

The stain is almost never below the hole.

Water enters a masonry wall at one point, travels inside the wall — down the back face of the brick, sideways along a mortar bed, a piece of flashing, a shelf angle or a framing member — and emerges somewhere else entirely. On a Chicagoland home the entry point is commonly several feet above and offset to one side of the damage you can see.

That single fact explains why so many masonry leaks get repaired twice: the first contractor fixed the wall behind the stain.

Paul Lally's Masonry Inc. has been tracing this work across Chicago and the Chicagoland suburbs since 1988. This is how the water actually moves, where it actually gets in, and how to find it before anyone starts cutting joints. Free on-site estimates: (708) 448-8866.

Brick is not waterproof, and it was never supposed to be

Start here, because it corrects the assumption most homeowners are working from.

Brick and mortar are porous. They absorb water. In a driving rain a brick wall takes on a significant amount of moisture through its face, and it always has. That is not a defect and it is not something a product fixes.

What keeps a masonry wall healthy is drying. Moisture absorbed during a storm evaporates back out over the following days. The wall is a sponge that is expected to wring itself out, and as long as it dries faster than it wets over the course of a season, it lasts a century.

Problems start in three ways:

1. Water enters through an actual opening — a crack, an open joint, a failed detail — rather than through the pore structure, so it arrives faster and in far greater volume.
2. Something blocks the drying — a film-forming coating, an interior vapor barrier, permanent shade, buried grade.
3. The wall's drainage system fails — on a veneer wall, the flashing and weep holes that are supposed to send water back out.

Nearly every masonry leak in Chicagoland is one of those three.

Two kinds of wall, two kinds of failure

Before you can diagnose a leak you have to know what you are standing in front of.

Solid masonry — brick two, three or four wythes thick, common on Chicago buildings built before roughly 1950 and on almost every bungalow, greystone, two-flat and courtyard building in the city. The wall's own mass is the weather barrier. Water gets partway in and dries back out. Failures are eroded joints, failed details at the top of the wall, and anything that soaks the wall faster than it can dry.

Brick veneer — a single four-inch skin standing an inch off a framed, sheathed wall, tied back with metal anchors. Standard on suburban construction from roughly the 1970s onward. The veneer is expected to leak; behind it, through-wall flashing catches water at the base and above openings and sends it back out through weep holes. Failures are almost always in that drainage path.

The tell: look at the base course for small open head joints every couple of feet. Those are weeps, and only veneer has them.

	Solid masonry	Brick veneer
What stops water	Wall thickness and drying	Flashing and weeps behind the brick
Typical era	Pre-1950 city stock	1970s onward suburban
Common failure	Eroded joints, failed crown/coping/sill	Blocked weeps, missing or reversed flashing, failed sealant
Wrong repair	Hard mortar, film coatings	Face-only repointing that never touches the drainage path

The entry points, in the order we check them

1. The chimney crown

The crown is the sloped slab across the top of the masonry that sheds water off the chimney — not to be confused with the cap, which covers the flue opening. A crown should overhang the brick with a drip edge so water is thrown clear.

An enormous number of Chicagoland crowns were simply troweled flush with the brick, so runoff pours straight down the face. Worse, a cracked crown is an open funnel into the middle of the chimney, and water entering there runs down the interior of the stack and shows up at a ceiling on the floor below — often nowhere near the chimney visually.

A chimney is the single most common source of a mysterious interior stain on a Chicago house. Four exposed sides, a top, no shelter, and a direct vertical path into the building.

2. Chimney and roof flashing

Where masonry passes through a roof, the joint is sealed with step flashing and counterflashing. Counterflashing must be set into a cut groove in a mortar joint and turned down over the step flashing.

What we find instead, constantly: counterflashing surface-caulked to the face of the brick. It looks fine for two or three seasons and then the sealant lets go, and the homeowner replaces a perfectly good roof over it.

3. The parapet and coping

On two-flats, three-flats and flat-roofed commercial buildings, the parapet is exposed on both faces and the top — the most weathered masonry on the building. Its coping (the stone, tile or metal cap along the top) is the roof of that wall.

Open coping joints let water directly into the core of the parapet, where it travels down inside the wall, freezes, and blows the parapet apart from within. A leak at the top floor of a two-flat is a coping or parapet problem far more often than it is anything else.

4. Lintels over openings

The steel over your windows, doors and garage openings rusts because water in the wall lands on it. As it corrodes it expands — rust jacking — and lifts the courses above, opening a horizontal crack.

That crack is then a wide-open entry point directly over a window. Water gets in, runs along the steel, and appears at the window head or the corner of the opening inside.

Rust staining weeping down the brick above an opening is the early warning, often years before the crack.

5. Window and door sills

A sill has two jobs: pitch and a drip edge. It must slope away so water runs off, and it must have a groove or projecting edge underneath so water drips clear rather than running back along the underside and into the wall below.

Over decades sills settle, lose pitch, crack across the middle, or get "repaired" with a mortar patch that fills the drip groove. Now the sill is delivering water into the wall instead of shedding it, and the courses directly beneath it will be the worst masonry on the elevation.

6. Sealant joints

The perimeter sealant at window and door frames, and the expansion and control joints in veneer walls, have the shortest service life of anything on a masonry building — often fifteen to twenty years. On plenty of 1980s and 1990s suburban houses they have never been replaced.

Failed sealant is an open slot into the wall. It is also one of the cheapest things on any masonry estimate.

7. Weep holes

On a veneer wall, blocked weeps turn a drainage system into a reservoir. We find them:

• Mortared shut by a previous repointing job by someone who thought open joints were sloppy work
• Buried under mulch beds and raised grade
• Packed with debris, insect nests or landscape fabric

If your veneer wall is wet and the weeps are closed, that is very likely your whole answer.

8. Open mortar joints on the weather elevation

The obvious one, and genuinely a major entry path — but note that it is number eight on this list, not number one. Joints recessed behind the brick face on a west or northwest wall let volume in during driven rain. This is what tuckpointing fixes, and it matters. It is just rarely the sole cause of a specific interior stain.

9. Below grade and at the splash line

Water at the base of a wall usually is not coming through the wall at all — it is being delivered there. A downspout discharging at the foundation, grade sloping back toward the house, a sump discharge running to the wall, or a window well with no drainage. The bottom three courses take splash-back thousands of times a season.

Reading the evidence inside

Where the stain is tells you less than when it appears.

• Only during and shortly after wind-driven rain → an above-grade entry point on the weather elevation. Chase the details above the stain.
• Hours after rain stops, or lasting for days → water stored inside the wall working its way out. Usually a larger entry higher up — crown, coping, parapet.
• Regardless of rain, worse in spring → groundwater and grade, not the wall face.
• In winter with no rain at all → often meltwater from snow banked against masonry, or condensation, or an ice-dam issue rather than a masonry one.
• Along a horizontal line at a floor level → shelf angle and its flashing on a veneer wall.
• At the top of a window → lintel. At the bottom → sill.
• Efflorescence spreading on the interior face → water is moving through the masonry in volume, carrying salts with it.

How we actually find it: the controlled water test

Guessing is expensive. Testing is not.

The method is simple and the discipline is everything: start low and work up, one small area at a time, with someone watching inside.

1. Wet only the lowest suspected area for several minutes. Watch inside. Nothing? Move up.
2. Next detail up — the sill, then the wall field, then the lintel, then the coping or crown, then the roof junction.
3. Stop at the first area that produces water inside. That is your entry point.

The reason to work bottom-up in small zones is that soaking the whole wall at once tells you only what you already knew — that the wall leaks. It does not tell you where, and where is the entire question.

The sequence that actually fixes it

1. Find the entry point. Everything else is guesswork until this is done.
2. Correct the water delivery. Gutters, downspout discharge, grade, sprinklers, window wells. Usually the cheapest line and the biggest effect.
3. Repair the detail. Rebuild the crown, reset the coping, replace the lintel with flashing and weeps, repitch or replace the sill, replace failed sealant with backer rod and proper sealant, open or re-drill blocked weeps, set counterflashing into a cut joint.
4. Repoint the failed joints — cut to roughly two and a half times the joint width, packed full, matched mortar, tooled to the original profile.
5. Let the wall dry. A wall that has been wet for years does not dry in a week.
6. Then, if appropriate, seal — with a breathable penetrating silane or siloxane sealer that lines the pore structure and lets vapor out.

Never a film-forming coating. Elastomeric and acrylic "waterproofing" paints close the drying path. On a Chicagoland wall that gets wet from behind, the trapped water freezes, expands, and pops the brick faces off, and then the coating blisters because water is pushing it off from the inside.

And never a sealer instead of a repair. A sealer reduces absorption through sound masonry. It does not close a hole.

Why waiting costs more

Water inside a wall is not a static condition, it is an active process:

• It freezes and expands through dozens of Chicagoland freeze-thaw cycles a winter, working joints open wider each season
• It corrodes steel — lintels, shelf angles, wall ties — and corroding steel expands and cracks the masonry around it
• It washes lime out of mortar, so joints degrade from the inside where you cannot see it
• Behind veneer, it reaches sheathing and framing, and that is no longer a masonry repair
• It carries salts that crystallize inside the brick and spall the faces off

A leak that costs a crown rebuild and some repointing this fall genuinely can cost a rebuilt wall section by spring.

Related services

• Chimney repair and rebuilds — crowns, caps and flashing, the most common source of interior stains
• Parapet wall repair — coping joints and the top of a flat-roofed building
• Lintel repair and replacement — rusted steel and the flashing that should have protected it
• Limestone and sill repair — pitch, drip edges and the courses below
• Tuckpointing and repointing — open joints on the weather elevation
• Masonry sealing and waterproofing — the last step, after the repair

Get it looked at before winter

If you have a stain that appears after storms, efflorescence spreading on an interior wall, rust running down the brick above a window, or a chimney you have never had inspected, have the water path traced before it freezes into the same joints again.

Paul Lally's Masonry Inc. is a family-owned, insured masonry contractor serving Chicago and the Chicagoland suburbs since 1988 — tuckpointing, brick repair and replacement, chimney repair and rebuilds, lintel replacement, masonry restoration, and waterproofing for residential and commercial properties. Built on Craftsmanship. Backed by Experience. We find the entry point before we write a scope, and if the answer is your roofer rather than your mason, we will tell you.

Free on-site estimates — call (708) 448-8866 or request one online.