Composite materials guide: Repair - Damage Removal

The first step is to remove paint and/or outer coatings. Chemical paint strippers must NOT be used, unless you know for sure they are specifically designed for composite structures. Most paint strippers are based on Methylene Chloride, and will attack cured epoxy resin (which is a common basis, or matrix material, for composite structures). Paint and coatings may be removed by:

Hand sanding — do NOT sand through any fibers of the undamaged structure
Wheat starch blasting
CAREFUL grit blasting or plastic media blasting.

It is important to check any repair manuals—such as structural repair manuals (SRM’s) for aircraft—or guidelines offered by manufacturers, and also to make sure all health and safety requirements are met.

After paint removal, additional damage assessment is performed, as hidden damage now becomes more apparent. Damaged composite skin may be removed by careful routing or grinding through the damaged surface. Note the following guidelines:

Routing is usually the method of choice for a solid laminate with through damage. However, for a thick solid laminate with damage only on surface plies, use careful sanding until undamaged plies are reached.
Routing also works well for a sandwich structure with damage into the core. Damaged cored should also be removed and can be routed out or cut & scraped out using a knife or other cutting tool.
Remove damage in circular or oval shapes, and do not use sharp corners. If an irregular shape must be used, then round off each corner to as large a radius as practical.