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Why one-part primers are rejected before fabric covering

Aviation Mechanic Airframe (AMA) practice question 21 of 30 on Non-Metallic Structures. ACS element AM.II.B.K11 · difficulty: standard. Want to answer it in a timed quiz? Use the Aviation Mechanic Airframe (AMA) practice mode.

Question bank updated 2026-09-22

QUESTIONA technician is preparing a cleaned steel tube airframe for covering. Why are one-part primers such as zinc chromate typically unacceptable for this step?

  1. AThe fabric adhesives dissolve them
  2. BThey cure too slowly for the schedule
  3. CThey add too much weight to the frame
Show the answer and explanation

Correct answer: A. The fabric adhesives dissolve them

  • A — correct The chemicals in the covering adhesives dissolve one-part primers, and adhesion of the fabric to the airframe is lost.
  • B — incorrect Cure time is not the stated objection; the problem is chemical attack by the adhesives and subsequent coatings.
  • C — incorrect Added weight is not the reason given; two-part epoxy primers are specified because they resist the adhesive chemicals.

BACKGROUND

Once the old fabric is removed, the exposed airframe must be thoroughly cleaned and inspected, with all old adhesive removed using a solvent such as methyl ethyl ketone. Required repairs, including removal and treatment of corrosion, are made at this stage. When the structure is clean, inspected, and repaired, an approved primer, or varnish on a wood structure, is applied in a step sometimes called dope proofing, and exposed aluminum must first be acid etched. Two-part epoxy primers and varnishes, which are not affected by the fabric adhesive and subsequent coatings, are usually specified. One-part primers such as zinc chromate and spar varnish are typically not acceptable because the adhesive chemicals dissolve them.

STUDY TIP

Tie the primer choice to the adhesive rather than to corrosion protection alone; the covering system, not the metal, drives the selection. Always use the product named in the supplemental type certificate you are working under.

KEY POINTS

  • Two-part epoxy primers and varnishes are usually specified before covering.
  • One-part primers are dissolved by the fabric adhesives, destroying adhesion.
  • Exposed aluminum must be acid etched before priming.

SOURCES

  • ama-airframe/ch03.txt "Preparation of the Airframe Before Covering"
Practice the Aviation Mechanic Airframe (AMA) test →Timed 100-question exam, by ACS area, or review your misses. Free.
MORE ON NON-METALLIC STRUCTURES

SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-31B Aviation Maintenance Technician Handbook – Airframe, and 14 CFR part 43. Regulations and handbooks are revised; confirm details against the current edition.