Fish Eyes in Third Epoxy Coat

I'm building a Sassafras 16 from the kit (MAS Epoxy, slow hardener).  I recently finished applying two coats of epoxy as a barrier coating and sanded the whole canoe down with 80 grit (Norton 3X sandpaper).  I sanded through in a few areas, but in other areas I think there were still some small (1/8" diameter) glossy indentations left.  I decided I should roll on a complete third coat to cover the bare areas and fill in the glossy indentations.  I vacuumed and then wiped the hull down with water a couple days ago, then vacuumed again last night before rolling the coat on.  It was fairly cool, maybe less than 60 deg F.  About 15 minutes after I started I noticed some fisheyes beginning to form in the epoxy.  I didn't realize what they were until I looked them up today, so at that point I didn't try to do anything about them.

The fisheyes are mostly 1/8" or less in diameter, although some of them are oblong and maybe a 1/4" long.  They are only on the #1 and #2 strakes (the 2 on each side closest to the keel).  The #3 through #5 strakes look fine.

Most of the stuff I've found about fish eyes says they are usually caused by some sort of contamination.  I suppose that's certainly possible but I can't think of anything I used that would have contaminated the second epoxy coat.  I realize now that I should have wiped the hull down with vinegar or laquer thinner to remove any contaminants, I'll definitely do this before applying any more coats.

I'm wondering if it's possible that the cooler temperature combined with the glossy indendations caused the epoxy to pull away.  I wouldn't expect that to happen, especially since the articles I've read say you can recoat after a "light sanding."

What  do you think?  Can I scrub with vinegar and then apply a new coat over the coat with fish eyes, or do I need to sand the fish eye coat down to zero glossy indentations before applying another coat?  Thanks for your help.



6 replies:

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RE: Fish Eyes in Third Epoxy Coat

Whoa.  Be Careful.  Stay away from laquer thinner.  Not sure, but I think that might disolve the epoxy!!!!  I know white vinegar is good for cleaning up uncurred epoxy, but not sure what it will do to the cured stuff.  Anyway, the thing to use is denatured alcohol.  Easey to get the Home Depot or Lowes. 

 I would lightly sand your fish-eyes, wipe it down and recoat the areas.  sounds like you are in the beach scratch area anyway.  Good luck


RE: Fish Eyes in Third Epoxy Coat

Thanks Paul.  I'll pick up some denatured alchohol on my way home tonight and give the light sanding and cleaning a shot tomorrow.

RE: Fish Eyes in Third Epoxy Coat

Vinegar, alcohol, and lacquer thinner all dissolve uncured epoxy. None of them dissolve fully cured epoxy.

RE: Fish Eyes in Third Epoxy Coat

I had the same problem and CLC recommended laquer thinner over the denatured alcohol.  To be honest I was never able to fix it.  I had no problems until the final coats on the deck. I tried washing with vinegar and rinsing followed by laquer thinner wih clean rags, and I am still fighting it.  I also used a 3m scotch pad to scuff the fisheyes.  I hope you have better luck than me.  Also a good cabinet scraper allows you to focus on the fisheyes.   Good luck!

RE: Fish Eyes in Third Epoxy Coat

You have to be careful of what kind of sandpaper you use on anything you want to paint or epoxy. Any sandpaper you buy at a hardware store is probably going to be some kind of clog resistant sand paper designed to be used dry. These sand papers are coated with wax, soap, silicone or some other release agent to prevent loading during dry sanding.

If you use only automotive grade sandpaper, and buy the highest grade as it will stay sharp the longest, you'll save time and money in materials.

 I recommend that you clean thoroughly by using wax and grease remover on your project, then wet sand thoroughly with 320 or machine sand with 220 gold coat or better, then clean again with the wax and grease remover, and re coat while the temperature is dropping, not rising.

For better flow out of resin, you can thin about 10% with denatured alcohol or an approved diluent, but watch out, thinner epoxy is more likely to fish eye, so you might want to do a small test area first.

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