Yes, steel lintels rust, but only when water gets to them and stays. A lintel behind properly flashed, drained masonry can last for many decades on a basic coat of primer. Rust problems almost always trace back to missing or failed flashing, blocked weep holes or a coating that was thin to begin with. The 2024 Ontario Building Code requires steel angle lintels supporting masonry to be prime painted or otherwise protected from corrosion (Sentence 9.20.5.2.(4)), and galvanizing is the common upgrade where a lintel is likely to get wet.
This post is about prevention: how lintels get wet, which finish to choose and how to look after the ones you have. If your lintel is already cracking the brick, see replacing a rusted steel lintel.
Why steel lintels rust
Ordinary structural steel corrodes when it's wet and exposed to oxygen. A lintel is at risk because of where it sits: at the head of an opening, which is exactly where water running down inside a masonry wall collects.
Masonry walls are not waterproof. Rain soaks into brick and mortar and some of it runs down the back of the outer wythe or the veneer. The wall is meant to catch that water and send it out, which is what flashing and weep holes do. The 2024 OBC requires:
- Flashing over openings in exterior masonry walls in most cases, specifically where the distance from the top of the window or door frame to the eave is more than one-quarter of the eave overhang (Clause 9.20.13.3.(1)(e)).
- Flashing that extends from the front edge of the masonry up behind the lintel (Sentence 9.20.13.4.(1)).
- Weep holes at no more than 800 mm apart, including in the cavities above lintels over windows and doors (Article 9.20.13.8.).
When those details are missing, damaged or blocked with mortar, water sits on the steel. Rust then does more than eat the lintel: it expands as it forms, and layers of rust can jack the brick above upward and outward, which is why rusting lintels crack walls.
How long do steel lintels last?
There's no reliable single number, and you should be wary of anyone quoting one. Lintel life depends on:
| Factor | Longer life | Shorter life |
|---|---|---|
| Water management | Flashing and clear weep holes | No flashing, weeps blocked |
| Coating | Galvanized, or galvanized and painted | Thin primer, or none |
| Exposure | Sheltered by a deep eave | Exposed wall facing driving rain |
| Location | Well above grade | Near grade, near downspouts, splash zones |
| Maintenance | Visible edge kept painted, sealant renewed | Rust left on the exposed edge |
| De-icing salts | None nearby | Garage door heads, entries near salted walks |
Older houses with simple primed angles and no flashing at all sometimes show lintels that are fine after many decades, and sometimes show lintels that have rusted badly. The difference is usually how much water reached them.
Primer, paint or galvanizing?
The code sets a minimum: prime painted or otherwise protected. Beyond that it's a judgement about how wet the lintel will get and how hard it would be to replace.
Shop primer
A rust-inhibitive primer applied in the shop is the baseline. It's appropriate for lintels behind properly flashed masonry that will stay dry. Primer is a thin coat, though, and it gets scraped and nicked in handling and setting.
Hot-dip galvanizing
Galvanizing coats the steel in zinc by dipping the fabricated piece in a molten zinc bath. A common specification for fabricated steel is ASTM A123. The zinc protects the steel in two ways: as a barrier, and by corroding first itself where the coating is scratched. That makes it more forgiving of handling damage and of the occasional wetting than primer alone.
Galvanizing makes most sense for:
- Exterior openings in walls with poor or no flashing
- Lintels near grade, at garage doors and anywhere exposed to splash or de-icing salts
- Replacement lintels, where you don't want to open the wall again
- Commercial and multi-unit work where the specification calls for it
Practical points: galvanizing happens after fabrication, so all cutting, drilling and welding has to be done first. It adds a step to the schedule. Field cuts or drilled holes through galvanized steel expose bare steel and should be touched up with a zinc-rich coating.
Galvanized and painted (duplex)
Where a lintel is visible and needs to match a colour, or where the specification demands maximum durability, the lintel is galvanized and then painted. Paint over galvanizing needs the right surface preparation and a compatible primer, so this is usually done by a coating shop rather than on site.
What doesn't help
- Caulking the bottom edge of the lintel to the brick. It blocks the drainage path and traps water on the steel.
- Mortaring over weep holes or filling the gap at the flashing.
- Painting over heavy, flaking rust without cleaning it back. The paint lifts off with the rust.
Painting an exposed lintel
Most of a lintel is hidden in the wall, but the front edge of the horizontal leg is usually visible above the window or door. Keeping that edge painted is ordinary house maintenance:
- Clean off loose rust and flaking paint with a wire brush or scraper back to sound metal.
- Prime bare spots with a rust-inhibitive metal primer.
- Topcoat with an exterior metal paint.
- Keep the weep holes and the flashing edge clear of paint, caulk and mortar.
This protects only the visible edge. It doesn't reach the part of the lintel inside the wall, and it won't fix a lintel that's already losing steel. If you see the warning signs (rust staining down the brick, a horizontal crack along the lintel, step cracks from the corners, brick lifting above the opening, or a lintel that has sagged), have it looked at by a qualified masonry contractor or engineer. Our guide to replacing a rusted steel lintel covers the signs and the repair options.
Getting the protection right on a new or replacement lintel
When a lintel is being replaced, or a new opening is being cut, it's the one time you can get every protection layer right:
- Size and bearing. The lintel has to suit the span and the masonry, with at least 150 mm of bearing on masonry, concrete or steel at each end. See steel lintel sizes under the Ontario Building Code and steel lintel bearing length.
- Coating. Decide on primer or galvanizing before the order goes in, since galvanizing has to be planned into the fabrication.
- Flashing and weep holes. Install flashing that runs from the face of the masonry up behind the lintel, with end dams where the detail calls for them, and weep holes kept open.
- Water sources above. Fix leaking eavestroughs, failed sills and open mortar joints, or the new lintel will be sitting in the same water as the old one.
Any lintel replacement in a loadbearing or veneer wall needs temporary support of the masonry and, depending on the scope, a designer and a building permit. Our guide on installing a steel lintel in an existing brick wall explains the process.
Ordering lintels with the right finish
We supply angle lintels cut to length, punched or welded as needed, and fabricate custom lintels to your drawings. Tell us the span, wall type and finish you want when you request a quote; we can prime or galvanize lintels to suit the job. See our steel products for what we make.
Frequently asked questions
Do steel lintels rust?
Yes, if water reaches the steel and stays there. A lintel behind well-flashed, well-drained masonry stays dry and lasts a long time. Missing flashing, blocked weep holes and a failed coating are what let lintels rust.
Do steel lintels need to be galvanized?
Not under the Ontario Building Code. Article 9.20.5.2. requires steel angle lintels supporting masonry to be prime painted or otherwise protected from corrosion. Galvanizing is one way to meet that and gives more protection where the lintel is likely to get wet.
Should steel lintels be painted?
The exposed edge of a lintel should be kept painted. If you can see rust on the visible face, clean it back and recoat it with a rust-inhibitive primer and an exterior metal paint, without blocking weep holes or sealing over the flashing.
How long do steel lintels last?
There is no fixed lifespan. It depends almost entirely on how wet the lintel gets and how well it was protected. Dry, primed lintels in older houses often last many decades, while a lintel in a wet detail with no flashing can deteriorate much sooner.
