Hi Ben,
Thanks for the detailed description of your problem. Certainly the epoxy coating resin should work the way you expect it to; allowing you to coat and overcoat, maintaining its clarity and being less susceptable to fish-eyes than most epoxies so there must be some cause of the problem.
First and most likely candidate is the epoxy infusion resin that you're applying a coat of onto the part...
The outer layer of the layup is .6mm veneer which has a thin coat of infusion resin applied to it at the layup stage
Does this mean that the infusion resin is painted onto the surface of your laminate and then effectivley cures in contact with the air (i.e. it's not enclosed into a mould, release film or something else)? If this is the case then the infusion resin will have a contaminated surface where its dilluents, agents and other additives will tend to accumulate 'blush' if it's in contact with the air. If this happens the surface will be very infriendly to overcoating, even if you rub the surface back this partially cured blush on the surface may well be hydroscopic and if not completly rubbed away will certainly cause the coating resin to fish-eye and if this blush has absorbed and trapped moisture then this could subsequently cause the 'whiting' of the resin that you describe.
The application of the coating resin at 2 parts res. to 1 part hard. is made with the resin largely bubble free, it is pored onto the surface and spread with mini foam rollers (held and gently dragged, not rolled).
That all sounds fine.
I have tried thin coats ( 36g. over 0.2m.sq) and experienced a lot of fish eye which i can only resolve by continuously spreading the resin as it thickens and eventually sticks with a less than smooth surface and still with fish eye in areas.
That is incredibly thin, 180g/sqm metre might be boyond any resin's ability to coat as thin as that wishoult fish-eying.
I have tried thicker coats ( 80g. over 0.2m.sq) and experieced very severe fisheye which can only be resolved by spraeding continuously as before in an attempt to make the resin stick. The result is a largely smooth surface but still with significant fish eye and a lot of milky whiteness due to the over agitation of the large amount of resin.
400g/sqm is more like it and should work perfectly fine. If the resin is fish-eying like this then you've certainly got some major contaminating on the surface, whether it's grease coming in somehow from the rubbing process (are you using a detergent when you wash the surface, if not you should be otherwise grease from your hands/skin can be a problem), whether it's the blush of the infusion resin or whether there is some really troublesome contaminating in the air or workspace (silicone being the worst of all, speak to any sprayer!).
1. Is the appearance of white patches in the resin that appear to be leaching something onto the surface of the resin. They cannot be sanded away and do not go away with the application of heat. Also they cannot take a coat of resin on top of them as the problem persists through the new resin. i attach a picture for your examination.
It's not clear from your description or the photo whether this 'white' contour layer is the original transition between the infusion resin and the coating resin, if it is, see notes above for explaination. If it's not and it's transition layers between multiple applications of the coating resin then this would be a real suprise and can only mean that you're introducing either moisture or some other contamination between layers of the coating resin. The most common explaination for this is when customers work in warm conditions but then leave the resin to cure in much cooler conditions. In the cool conditions, condensation can form on the part and then the longer cure time (caused by the lower ambient temperature) combined with the moisture means that the epoxy can start to absorb moisture before it cures. The solution to this is to ensure that the part cures fully in a warm, dry environment.
2. Due to the thin wood veneer it is immensely difficult to judge at what point to stop sanding in the attempt to get a flat surface and any "rub through" is pretty much guaranteed to damage the veneer beneath, and anyway i cant work out an effective way of adding another coat of resin with any kind of decent finish on a surface that has uneven patches of wood and resin.
The only way to avoid 'breaking through' is to ensure that you start off with a thick enough layer of clear resin to cut into so we need to resolve whatever is causing the problem. Have you tried testing the resin and the process in a fresh situation? - Maybe move where you're working, apply some coating resin to a piece of wood (this takes the infusion resin out of the equasion), let that cure to a 'B' stage and then apply some more epoxy to that, cure to a 'B' and apply some more. You should find that all 3 applications will go on without fish-eying. Allow to cure FULLY (12hrs) and then flat and polish. You should get perfect results. From there, you can start to reintroduce the elements of your particular project to see where the process comes unstuck.
I hope this helps.
Matt
Matt StathamEasy Composites / Carbon Mods - Technical Sales