What is hem rust on a car door?

Rust along the very bottom edge of a door, bonnet or boot lid is coming out of the hem. That is the fold where the outer skin wraps over the inner one. Water gets into the fold and sits there. Folded hems are a place corrosion starts on aluminium panels too.

What kind of repair does it need?

Cutting back to sound metal, treating it and painting. A proper repair opens or replaces the hem, because the corrosion is between the two skins. Grinding the outside leaves the cause in place.

Class of work Cut back, treat and refinish, or new metal let in where it has spread.

The repair goes out to where the metal is still sound. That is usually wider than the bubbling you can see.

What to do next

Expect the repair to be bigger than the rust you can see. Be wary of a cheap quote to make a hem rust spot disappear. Ask if they are treating the inside of the fold. Check the drain holes at the bottom of every door are clear.

Sources

  1. Aluminum Associationindustry associationCrevices (narrow openings) at mating surfaces can collect…
  2. Axaltapaint makerPaint has to be stripped/sanded back to the bare metal
  3. PPG GBpaint makerStrip the paint from the affected area down to the bare metal, remove all existing corrosion, treat the surface with the correct metal treatment fluids and etch primer, and repaint
  4. EZ Tech PDRrepairerThink about how a door skin wraps around an edge or how a quarter panel meets an opening. Those areas are hemmed, doubled, or braced…
  5. GarageWeldingblogA rust hole is usually larger than it looks.

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Related

What is surface rust on a car? Light brown staining with the paint still smooth is rust at its earliest and cheapest stage. Learn why acting now saves money. What is rust under car paint? Blistered or bubbled paint means rust is growing underneath, usually wider than it looks. Learn what repair it needs. What is rust through on a car? A hole or soft jagged metal means corrosion has eaten all the way through the panel. Learn how the repair cost compares with what the car is worth. What is filiform corrosion on a car? Fine worm-like tracks creeping under the paint on aluminium panels are filiform corrosion. Learn why this is not rust.
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