Many homeowners notice a distinct, stair-step crack forming in the mortar joints above their windows and immediately worry about a failing foundation. However, in the vast majority of Chicago brick buildings, the culprit is much more localized: a failing steel window lintel.
What is a Lintel?
A lintel is the piece of angled steel installed horizontally above a window or door. Its job is to support the immense weight of the masonry above the opening.
What is "Rust Jacking"?
Over decades of exposure to Chicago's humidity and rain, the steel lintel inevitably begins to rust. As steel oxidizes and turns to rust, it expands to several times its original thickness. This phenomenon is known as "rust jacking" or "oxide jacking."
The expanding rust is so powerful that it physically lifts the courses of brick above the window. Because masonry is rigid and cannot flex, it cracks. The crack typically follows the path of least resistance — the mortar joints — creating that signature stair-step pattern moving upward and outward from the corners of the window.
Why Caulking Isn't a Solution
Caulking the crack is a temporary band-aid that actually accelerates the problem. It traps moisture inside the wall, speeding up the rusting process of the steel lintel.
The Permanent Repair
The only permanent solution is structural. At Star Tuckpointing, we temporarily shore up the brickwork, remove the rusted steel, install a new, properly flashed and primed steel lintel, and rebuild the masonry above it so it matches seamlessly.
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