I'll be laying up my GRP bodywork over a foam buck. What am I best coating this with? flowcoat, then body filler? Flowcoat mixed with an easy sand filler powder, then body filler, just body filler and loads of it?

Just go for the flowcoat or use ordinary gelcoat and seal with polyester? film.

The film seals the gelcoat so it sets without the wax additive, and you can use the film (which is quite thick) to make surface smooth, without the need fro sanding

CFS do the film, but ran out when I last ordered some!

ATB

Simon

Thickish flow coat sanded down would be my choice.
Of course you don't want it too thick because

1) it'll just cost more
2) it's quite heavy
3) it's non structural

In this order of preference: Tooling gelcoat, flowcoat, or gelcoat (with wax). Seal and release with release wax (Mirrorglaze or similar). I have also made moulds by just spraying with automotive spray paint, followed by release agent, but some paints are attacked by the resin used.

I was under the impression that you could give a skim coat of body fill over the glass with no gel coat and then treat as normal--- I need to know also as I have most of my body parts ready for this procedure.
Dale

Found this a while back which seems to be the same/similar technique.
He uses bondo aka body filler.

http://www.rqriley.com/frp-foam.htm

Body filler will work, but it can be quite porous, so I normally coat with paint to seal it (checking first that the paint doesn't dissolve in the planned resin). If your foam buck is perfect, then body filler just makes more work, if it is rought and needs smoothing, it might be your best option.