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Preferred primer for dissimilar metal joints

Aviation Mechanic General (AMG) practice question 15 of 31 on Cleaning and Corrosion Control. ACS element AM.I.G.K15 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic General (AMG) practice mode.

Question bank updated 2026-09-22

QUESTIONFor protecting dissimilar metal joints not involving magnesium, which primer does the handbook identify as preferable?

  1. AEpoxy primer
  2. BA Bonderite conversion coating
  3. CA coat of waterproof wax
Show the answer and explanation

Correct answer: A. Epoxy primer

  • A — correct The handbook calls for a minimum of two coats of zinc chromate or, preferably, epoxy primer on all dissimilar joints not involving magnesium, in addition to normal primer requirements.
  • B — incorrect Bonderite is the chemical applied in the alodizing process; it is a conversion coating, not the primer specified for dissimilar joints.
  • C — incorrect Waterproof wax is the overcoat applied to polished unpainted aluminum surfaces after treatment; it is not a primer.

BACKGROUND

Certain metals corrode when placed in contact with other metals, a process called electrolytic or dissimilar metals corrosion. All dissimilar joints not involving magnesium are protected by a minimum of two coats of zinc chromate or, preferably, epoxy primer, in addition to normal primer requirements. The primer is applied by brush or spray and allowed to air dry 6 hours between coats. Joints involving magnesium receive the same primer coats plus a layer of pressure-sensitive vinyl tape, or extra primer coats when tape cannot be used.

STUDY TIP

The handbook names two acceptable primers for dissimilar joints and states a preference; know both names and which one is preferred.

KEY POINTS

  • Dissimilar joints get at least two coats of primer
  • Zinc chromate is acceptable; epoxy primer is preferred
  • Primer is applied by brush or spray and air dried 6 hours between coats

SOURCES

  • FAA-H-8083-30B ch08 "Contacts Not Involving Magnesium"
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SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-30B Aviation Maintenance Technician Handbook – General, 14 CFR part 43 and part 65. Regulations and handbooks are revised; confirm details against the current edition.