Why rust stains appear above windows and doors

Brick above a window or door opening cannot hang in the air. A steel angle called a lintel carries it. On homes of the rowhome era, that lintel is usually a plain steel bar hidden behind the brick. You never see it until it starts to push or bleed.

Water and oxygen cause exposed steel to rust. Water can also get behind the brick and sit on the steel. Contractors check for failed flashing above the opening, blocked weep holes and cracked mortar joints. The right drainage detail depends on how the wall was built.

Rust takes up more space than the steel it replaces. That expansion can push the rigid brick courses upward and outward. Restoration contractors call this rust jacking.

Older steel lintels may have worn coatings or outdated drainage details. A century-old house may also have had earlier repairs. Do not assume the steel or flashing is original; ask the mason to check its condition.

• Stage one is a stain. Brown or orange streaks run down from the steel above the opening. The steel edge may show flaking, pitting or bubbled paint.
• Stage two is a horizontal crack. A crack opens in the mortar joint directly above the window or door, where the expanding lintel lifts the course.
• Stage three is stair-step cracking. The crack steps up and out from the corners of the opening through the mortar joints.
• Stage four is movement. The brickwork above the opening bows outward, brick faces spall off, and pieces can come loose or drop.

These signs can overlap; they are not a diagnosis or a fixed timetable. Rust stains alone do not prove the lintel has failed. Cracks can also come from other movement. A mason should inspect cracked, bowed or displaced masonry, not just cover the stain.

A stain by itself is not usually a same-day emergency, but it deserves an inspection. Continued water exposure can worsen corrosion. Freeze-thaw cycles can widen cracks and let in more water. Delaying repairs may increase the scope, especially if brickwork moves or breaks.

Two warnings from the trade are worth repeating. First, do not caulk the cracks. Caulk seals moisture against the steel and makes the rusting faster, while the movement continues underneath. Second, treat bulging or loose brick as urgent. Full collapse of a wall is uncommon, but falling masonry over a doorway is a real risk. If brick has already dropped, keep people away and call someone the same day.

At the staining stage, with the steel still sound, the repair is maintenance. The mason opens a few courses to expose the lintel. Rust gets ground or brushed back to sound metal, then coated with a rust converter and primer. Then the brickwork is rebuilt or repointed. Treatment can slow corrosion if water entry is corrected, but it cannot restore lost steel.

A badly corroded lintel may need replacement. A mason or structural engineer must assess the support, remaining steel and surrounding masonry. Replacement involves supporting the brickwork before removing the damaged lintel. The new lintel must be properly sized, with suitable corrosion protection. The courses above are rebuilt with matched brick and compatible mortar.

The step that decides whether it lasts is not the steel. The failed flashing and weep holes must be corrected too. Otherwise water goes right back onto the new lintel. Paint alone cannot repair weakened steel or failed drainage. A quote that covers brick but says nothing about flashing is worth questioning.

We found no published Philadelphia-specific figure for lintel replacement. These are national and regional numbers, for sizing the job rather than pricing it.

Angi’s 2026 cost data puts a simple window or door lintel swap at $280–$640, averaging $460. Contractors report higher figures once masonry is included. Pittsburgh masonry contractors quote $1,500–$3,000 for a single ground-floor opening, rising to $2,000–$5,000 with staging. Chicago sources report $800–$2,500 per lintel, and $2,000–$5,000 when the brick above is reset. Brick-heavy rowhome work will sit in the contractor ranges, not the low one.

A real price needs somebody at the house, because the flashing condition changes the scope more than the stain does. The fuller picture, with each figure’s confidence stated, is in what masonry work costs in Philadelphia and Delco. Lintel work is one of the lintel services local masons quote through us.

• Look at the exposed steel edge at the base of the opening. Flaking rust, pitting or bubbled paint means active corrosion.
• Measure or photograph any crack. A hairline in the mortar joint is common. A stair-step crack running from a window corner is not.
• Check the photo again in a few months. A crack that has widened is a wall that is still moving.
• Never stand or work under loose or bulging brick above a doorway.

If you are unsure which stage yours is, that is exactly what photographs are for. Submit them once, and the masons who look at the house will tell you which kind this is.

Other guides in this series cover problems a homeowner can spot from the ground:

• Spalling brick — what a flaking face means, which kinds wait, and which need a mason now.
• Leaning chimney — what a gap between chimney and house means, and why it is urgent.
• Masonry prices in Philadelphia and Delco — published price ranges for common work, with each figure’s confidence stated.

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

• RestoreWorks, Common Causes of Lintel Corrosion and How to Prevent It
• Delta Tuckpointing, Lintel Repair for Steel and Stone Windows
• Star Tuckpointing, Rusted Window Lintel Replacement and Stair-Step Cracks
• Ciriello Contracting (Pittsburgh), Rusting Lintels
• Integra Inspections, Cracked Brick on Exterior Walls
• Angi, What Does Lintel Repair Cost? (2026)