[Pitar]

Polyester or polyurethane resins, not epoxy, are used in laminating any composition (carbon fiber, glass fiber, etc.) of weave due to its rigidity. I use for aircraft laminate structures for lay-ups and repairs.

Polyester resin sands easily, epoxy resins typically don't because of their flexible nature, unless formulated as finishing resin for very lightweight cloths used in the radio control airplane and boat hobbies to repel the chemical attack of nitro-methane fuels.

Emerald uses a polyester resin. It sands and polishes up very nicely. As a kid in southern California I worked in a surfboard company. Polyurethane resin was used to wet-out the glass cloth over the interior foam structure. It sanded easily and could easily be polished to a gloss.

Polyester or polyurethane resin can be thickened with ground up cloth (called flock) to create an easily formed rigid structural filler for strengthening where needed. Because it's used in a normally non-visible area, after its application and shaping aesthetic attention is unnecessary.

Sanding through and into the cloth of any composite structure creates a weakened point in the over all strength of the contiguous surface. The area where the string ends are secured is one such area on a composite guitar top.