epoxy coating resin issues


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benet
benet
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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.

The infusion resin is sanded with 120 wet paper and wiped clean with a clean damp microfiber cloth and allowed to dry before the coating resin is applied at an ambient temperature of 25 C.

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).

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.

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.

Both thick and thin require significant sanding back to get to a clear flat finish and in this process (starting 180 grit wet going to 1200wet ) i get 2 even bigger problems. 

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.

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.



Any help would be greatly appreciated, at this point im thinking varnish ? or GC50 polyester gel coat ?

Thanks

ben
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benet
benet
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Thanks for that Matt, its hopefully very useful.

Things i may have gleamed from it and will try changing.

Clearly the excessive fish eye is the root of the problem and its cause must be addressed.

The infusion coating is covered by release film in the press and comes out embossed with the image of the film on it so im hoping that means im not getting a blush from it which incidentally you dont clearly explain how to clean off, although you say wet sanding may not be sufficient? I would say that at any point when i wet sand im trying to get a flat surface before the next coat is applied so it is not just a quick roughing up.

It is possible that the microfiber cloth was contaminated with silicone from some  previous job ! Arrghhhh. I will replace it and keep it separate !!

I will stick to applying with the thicker coating.

In this case i was not attempting to apply further coats during the b stage but rather allow the resin to cure then sand and re-coat. However i didnt get to re-coat yet as i have this whiting problem.

I do not think that the whiteing was a transition layer however it may be the case that i had not allowed the resin to fully cure before sanding, certainly i had not waited 12 hours, more like 6 or seven at 25C , the epoxy seems to sand well at this point but my worry is that the heat of the sanding softens it up and allows moisture into it causing my problem. Does this sound possible?

I am learning, the hard way, that there are no short cuts in this process and attention to possible contamination is vital.

thanks for you help.

Ben
Matt (Staff)
Matt (Staff)
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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
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