confusion re: vinylester and polyester

[tomdeacy]

I am working on a Mark II gray body. I have ground out the seams and in most locations the gelcoat seam did not go very far down. On the locations that were deep I have applied the vinylester based 3M HSRP. I understand this is necessary for strength and bonding the vinylester based fiberglass to the vinylester based filler. What I don't understand is how I can use polyester based Rage Gold over the parts of the seams that have been ground to the fiberglass but not deeper. Isn't the fiberglass, no matter how deep, a vinylester composition? And, if so, how does the Rage Gold get a good chemical bond with it? Further, how can I use Rage Gold to fill in the rough fiberglass under the hood, if that fiberglass is also vinylester based? What am I missing here? Thanks Tom

[tomdeacy]

To address this issue a little further, if compatability between vinylester and polyester is a problem, why are these bodies made with a vinylester based fiberglass and then coated with a polyester based gelcoat? I'm not questioning that it can be done because FFR has been supplying these bodies for years. I'm just wondering why there is ever a compatability issue and how careful we must be to coat a burnthrough sanding of the gelcoat before applying a polyester based glaze or featherfill like product over it.

[Streetrodpainter]

the main problem that I have found is that if you use a polyester based product to fill deep voids, seams or holes, it will expand and contract at a different rate. it is not that it is not compatible, just that it will not expand and contract the same, therefore exposing the hole, seam void etc. you can skim over the top with rage(polyester based) as you are tying in the polyester gelcoat surface only. good luck, cheers, SRP

[tomdeacy]

Answers my question exactly. Thanks once again. Tom