I am having several issues using your epoxy coating resin as a top coat over a laminate  composite layup consisting of wood and glass fibre. The outer layer of the layup is .6mm veneer which has a thin coat of infusion resin applied to it at the layup stage in order to give an even colour when the laminate comes out of the press. (previously some infusion resin had soaked through the veneer and given a patchy look to the outer surface even after the coating resin had been applied.

Further..

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 Statham
Easy Composites / Carbon Mods - Technical Sales

Thanks for that Matt, its hopefully very useful.

Hi Ben,

Again, that's useful feedback. A customer (a professional sprayer) told me a story yesterday, I don't know how true it is, that a Bentley that another company had sprayed (and £30,000 paint job) had come in to him to be re-sprayed after the paint finish was unacceptable. The previous sprayers had battled with fish-eyeing and the repair work they did was visible in the paintwork so it all had to be done again. The problem was finally traced to a can of 'Pledge' furniture polish that has been used inside the car (but inside the workshop) which contains silicone. The silicone particles in the air caused the paint to fish-eye and cost the company the £30,000. If you've used that microfibre for anything along the lines of polishing in the past then it might well be the cause. Also, wet sanding when resin is only partially cured could well be another problem. If you'r insure, but the part somewhere really warm (40'C) to cure off fully before wet sanding.

I hope it starts to come good for you.

--Matt

Matt Statham
Easy Composites / Carbon Mods - Technical Sales

Hi Matt,

I can confirm Matt's story about the silicone in the air. Once I've coated a part with epoxy and few meters away I sprayed a door hinge with silicone- just a mist...immediately I saw the epoxy forming fish eyes...I couldn't believe it!!!!...I was wondering how could this be possible so many meters away with such a small amount of silicone spray??? 

Hi Ben,

One small thing, ive just contacted a old friend who has a paint shop and oven. If i give him my finished boards to sit in his oven for a while, how long? how hot? and what sort of effect will this have on the overall strength , impact resistance and flexibility of the epoxy used?

Post-curing, if done properly, can only ever be a good thing for epoxy resin although, over enough time just at ambient temperature, the resin will naturally reach something very close to a post-cured resin (it will just take a huge amount longer). The exception is where resins will be used at high temperature - they should always be post-cured up to this operating temperature before use.

In terms of post-curing your boards, I would recommend a moderate post-cure as follows:

6hrs at 40'C
4hrs at 50'C
4hrs at 60'C

This steady ramp and not excessively hot post cure will ensure full cure of the resins without putting too much strain on them. The difference you would expect would be a harder feeling resin with more fully develped structural properties (and more of a 'ring' when you hit it, rather than the 'thud' of a resin that's not fully cured).

--Matt

Matt Statham
Easy Composites / Carbon Mods - Technical Sales