I've just finished a plug and a mould for a GSXR Dragbike tank cover, I had the same issues with the High gloss Pattern coat, stripey and rather uneven, even on top of a completely flatted down cover of Pattern Coat primer.
(I can paint 2-K boat varnish with the type of brush I used, to a level that looks like it is sprayed on ... I've had years of practice on boats ...)
I also had to use 240 grit on a circular sander to speed up my work.. I had to sand so much down that i broke through the high gloss i a few small places, so I decided to try spraying the High Gloss, using the Gel-coat cup gun.. That actually worked MUCH better, the second coat was much smoother
But it still had som areas of "orange peel texture" I sanded this down using dry 400 grit, then went up to 1500 wet sanding .. I Polished only with coarse compound, since I wanted a satin finish in the plug and mould. The (Unimould) mould came out very nice, even though I was in a dreadful hurry and did the whole process in less than 24 hours....
I then did a small test, and thinned the High Gloss Pattern Coat with around 8 % Acetone ... then brushed it on ... MUCH better result ... Might be worth a try, If you can not spray your plug...
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