Parent material and what goes with it
Where to buy| Parent part | Patch and filler | Fasteners and contact | Watch for |
|---|---|---|---|
| Fibreglass laminate (fairings, covers, honeycomb facings) | Same fabric and resin family as the part; putty of room-temperature resin and clean short glass fibres only for damage in the first ply | No galvanic problem with most fastener metals | Wet layup cured at room temperature does not restore the strength of a 250 or 350 °F cured part |
| Carbon laminate | Titanium or precured carbon/epoxy for highly loaded parts; aluminium only over one layer of fibreglass cloth | Titanium (Ti-6Al-4V is the most common) or stainless; no aluminium fasteners; cadmium plating cathodic | Carbon is cathodic against aluminium and cadmium; rivets are not used |
| Aramid (Kevlar) laminate | Same aramid fabric; protect the repair from moisture | Fibreglass and aramid do not cause fastener corrosion with most metals | Absorbs up to 8 % of its weight in water; weak in compression; fuzzes and is hard to cut |
| Aluminium-faced sandwich | Viscous epoxy for dents, scratches or fractures up to 1/4 in; delaminated dents are repaired, not filled | Bolted repairs are not used in honeycomb sandwich | Core replacement: same material and cell size; wood or glass-fabric honeycomb may substitute where permitted |
| Honeycomb core, composite panel | Plug of the same type, class and grade, cells lined up with the parent | Potting for hard points where bolts or screws go | Potting is heavier than core: control surface balance |
FAA-H-8083-31B Vol. 1 pp. 7-5, 7-25, 7-34, 7-35, 7-43 to 7-46; AC 43.13-1B Chapter 3 pp. 3-1, 3-2 and 3-9. The SRM names the actual material, grade and fastener for each repair.
Same material, or an approved substitute
AC 43.13-1B says repair materials must preserve the strength, weight, aerodynamic characteristics or electrical properties of the original part. It adds that the best way is to replace damaged material with material of identical chemical composition or a substitute approved by the manufacturer. The same note asks you to review the safety data sheets and to observe shelf life.
Mixing families is where repairs go wrong: a different resin can bond poorly to the old one, a different fabric changes stiffness and weight, a metal patch changes the electrical and corrosion picture.
Cutting and drilling each fibre
Glass and carbon wear high-speed steel quickly: diamond-grit or carbide tools, high speed and slow feed. Glass is drilled with the same bits as carbon. Aramid is softer, so high-speed steel works, but it must be held and cut with a shearing action over a plastic backup plate, with scissors that have one serrated blade. Clean the serrations right after use or uncured resin ruins them.
Questions people actually ask
Can I patch carbon with aluminium?
Yes, with one layer of fibreglass cloth between them and with titanium or stainless fasteners. Titanium or precured carbon patches are preferred for highly loaded parts.
Can fibreglass repair a carbon part?
Not as a structural substitute: the repair must match the part's strength and stiffness. Fibreglass is used as the isolation layer against aluminium, not as the repair ply.
Why is aramid difficult to repair?
It fuzzes when cut, is weak in compression and absorbs water, so the repair is cut by shearing and sealed against moisture.
Limits — when NOT to use this
What the sources support, and no further.
- No material grades. Fabric styles, resin systems and core grades come from the SRM; this page lists compatibility rules only.
- Metal parts. Only aluminium-faced sandwich is covered; sheet-metal repair is in the sheet-metal guides.
- Rows are summaries of handbook paragraphs and may not fit your aircraft.
Where to buy
Distributors coming soon.
Sources
- FAA-H-8083-31B, AMT Handbook — Airframe, Volume 1 (2023), Chapter 7 — p. 7-5, glass, aramid and carbon fibres; p. 7-25, wet layup; pp. 7-34 and 7-35, potting and core plug; pp. 7-43 to 7-46, bolted repairs, patch and fastener materials; p. 7-52, cutters for carbon, glass and aramid.
- AC 43.13-1B, Change 1, Chapter 3, Fiberglass and Plastics — p. 3-1, paragraph 3-1, material to preserve strength, weight, aerodynamics and electrical properties; p. 3-2, putty; p. 3-9, aluminium facings and core substitution.