When fixing a ding or glassing on fins do you need to mix a little styrene into the resin mix so that you can tidy the repair/job up with Ali oxide paper afterwards or not?
It is not stryene that makes sanding easy, it is Surfacing agent (styrene/paraffin wax mix).
To answer your question though, do not add SA to the lam when doing repairs, or glassing on a fin. It can cause bonding problems. Paraffin wax in SA rises to the surface to make things sandable, so make sure that the area that you add it to is facing upwards. A couple of ways to tidy up are:
1.use a grinder to tidy up the lam, it will not clog like sand paper, but you must be careful not to mess up, then hotcoat and sand as usual
2. lam as usual, hotcoat, then sand and tidy things up, then hot coat again to cover up exposed cloth that is inevitable from not cleaning the lam up before hotcoating, sand as usual after the 2nd hotcoat.
hope thishelps. good luck
Thanks for your help astevens i’ll be buying myself a grinder then!