Water Leak Through a Brick Wall? Start Here

Water showing up inside a brick wall is a symptom, and the wall is rarely the whole story. Brick walls are built to let some water in and send it back out through flashing and weepholes. A leak means that system is failing at one spot: joints, a sill, a lintel, the top of the wall, or where the wall meets a roof. Find that spot first. Sealing the wall before you know the source is the most common mistake.

Where is the water getting in?

Work from the outside, starting with the wettest spot inside and looking higher. Water often travels before it shows. The usual entry points:

• Open or crumbling mortar joints. The City requires masonry joints to be kept weather resistant and water tight (City of Chicago). Our guide on signs your brick needs tuckpointing shows what to look for.
• Sills and the tops of windows and doors. The Brick Industry Association says through-wall flashing belongs at sills and at the heads of openings, collecting water behind the brick and sending it back out (BIA). Over a steel lintel, flashing and weepholes belong at the lintel level (BIA). Rust stains below a window are a clue (lintel failure signs).
• The top of the wall. Caps and copings exist to channel water away from the wall. Brick caps, with many mortar joints, are a weak choice at the most exposed spot (BIA).
• A chimney or roof edge. Flashing belongs where a chimney meets the roof and at the base and top of walls (BIA). A roof leak can look like a wall leak.
• Things that are not the brick. Gutters or downspouts spilling onto the wall, a pipe, or window and door frames that no longer seal. A mason can tell which.

How do you check it?

1. Note when it shows up. After rain, after snow melts, or all the time? That tells you a lot about the source.
2. Look outside, up and down the wall for open joints, cracked or missing mortar, crumbling brick faces, cracked sills and missing caps.
3. Look for white powder on the brick. Efflorescence needs salts, water and a path to the surface. Appearing after the first year, it usually points to extra water getting in or poor drainage (BIA). It is usually harmless on its own, but it tells you the wall is staying wet. See efflorescence on brick.
4. Take photos with dates. A mason, a building owner or the City will want them.

Should you seal the brick?

Not first. The BIA says to find and fix the moisture cause before dealing with efflorescence, and that coatings alone are not recommended to control it (BIA and NPS). The National Park Service says water repellent coatings are appropriate only after a building is made watertight and dried (NPS). That guidance was written about early American brick generally, not Chicago common brick, but the order of operations holds: fix the entry points, let the wall dry, then ask whether a coating is needed at all. Our sealing after tuckpointing article covers that decision.

If the cause is open joints, the fix is repointing with mortar that is softer and more vapor permeable than the brick and no harder than the original (National Park Service). If it is a lintel, sill, cap or flashing problem, it is a repair on that part. A leak that has run for a long time can also have damaged the wall behind the brick, so get a mason on it early.

Water coming through your wall? Akats finds the entry point, repairs it and handles the permit side if one is needed. See our masonry service or the Chicago brick and masonry repair guide.

Common questions

This article explains general rules and common situations in Chicago. It is not legal advice, and City rules change. For a specific property, check with the Chicago Department of Buildings or a licensed professional.