Rusted Steel Door Repair Toronto: Rotted Bottoms, Rusted Frames & What to Do Before Winter (2026)

A steel door is a thin steel skin wrapped around a core. The paint and the factory coating are what keep it from rusting. Once that coating is broken, usually at the bottom edge, at a scrape from a cart, or where the weatherstripping has worn away, water gets to bare steel and rust starts.

The bottom of the door and the base of the frame get the worst of it. Rain runs down the face of the door and collects at the bottom rail. In winter, salt is tracked in and shovelled against the door, and meltwater sits in the corner between the frame and the floor or concrete. Salt speeds up rust a great deal, which is why so many back doors, exit doors and doors next to parking lots look worse every spring.

Rust also starts inside. Condensation forms inside the door and frame when warm indoor air meets the cold steel, and water that gets behind a damaged bottom edge has nowhere to dry out. By the time you see bubbling paint, the steel underneath has often been rusting for a while.

If the frame is still good, a new door can often be hung in the existing frame, which keeps the cost and disruption down. If the frame has rotted at the base, it's repaired or replaced along with the door. For a deeper look at the decision, see steel door repair vs replacement.

Steel frames, especially hollow metal frames set in masonry or concrete, rust from the floor up. Water and salt sit in the corner where the frame meets the floor, and because the frame is hollow, the inside rusts where no one can see it. The first sign is often the bottom few inches of the frame looking swollen, flaking, or simply gone.

A rotted frame base causes problems beyond looks. The hinge side loses support so the door sags. The strike side moves so the latch misses. And on an exit or back door, a weakened frame is easier to force. See door reinforcement for securing weakened openings.

Depending on how far the rust has gone, the bottom of the frame can be repaired, or the frame replaced. On commercial openings this is often done together with the door. See hollow metal door and frame replacement.

Back and exit doors at plazas and restaurants

Rear doors face lanes and parking areas where salt and slush collect, and they're used constantly for deliveries and garbage. See commercial back door repair.

Warehouse and industrial man doors

Doors next to loading areas and overhead doors get splashed by trucks and forklifts all winter.

Apartment and condo building service doors

Garbage room, parking garage and stairwell exit doors, where meltwater from cars runs to the door.

Home entry and side doors

Steel entry doors on homes, especially side doors along driveways and back doors onto decks. See back and side door replacement.

For more cold-weather problems, see winter door problems in Toronto and winter-proofing commercial doors.

See the commercial door repair cost guide and the residential door repair cost guide.

Also useful: steel door repair vs replacement, door slab replacement, commercial door maintenance, fire door inspections and common door problems in the GTA. Services: residential door repair, fire exit doors, break-in repairs and emergency door repair.