I have sprayed 600 microns of gelcoat fire retardant.After 24 hours curing when i sand the surface for finish with 400 grit sanding paper whitish spots become visible on the surface which become more prominent after clear coat sometimes resin tearing or resin separation although i spray layer to layer with flashoff time 20~30 sec. 1% of MEKP used.

Last time i had checked the airline but there were no any contamination and air line was completely dry.

1% is low for a gelcoat, typically... Is that what the manufacturers recommend catalysing at?