On Wednesday, November 7, 2012 8:18:29 AM UTC-5, RL wrote:
FWIW, let me offer some information on gel coat. Beginning with

coatings terminology –



Paint – Dries when solvent vehicle evaporates. There are thousands of

formulations and variations.



Gel Coat – Cures during the molecular crosslinking (polymerization)

process. Technically known as “unsaturated polyester gel coat”, this

product is formulated as an in-mold coating for molded composites

parts. With a few exceptions, almost every sailplane has been produced

with in-mold gel coat, including those that are post-finished with a

polyurethane “paint” as a secondary coating.



Polyester Topcoat – Cures and dries. A hybrid consisting of

unsaturated polyester resin formulated with a solvent vehicle.

Products such as Prestec and Duratec are topcoats, not gel coat. Used

for re-finishing original in-mold gel coat surfaces.



I've seen others make this distinction whenever this topic comes up. BUT gel coats can also be applied as topcoats. The MGS (Scheufler) website has a nice document that explains the different methods for applying T35 in mold or as a topcoat. When applied as a topcoat "to repair small areas, the following procedure can be used: Add 10% Thinner HF to the gelcoat, mix thoroughly with 10% Hardener SF. Add an additional 10 - 30% acetone." The instructions go on to describe the spray technique which involves thin coats, leaving enough time for the solvents to "disappear" (5 to 10 minutes) followed by additional coats likewise laid wet on wet.