Fisheyes in Epoxy? (pics)

[Tetsuaiga]

I am repeatedly having problems with fisheye appearing after applying west 207 epoxy on a piece.

My process has been wash with water and mirca abrasive nonwoven pad, clean up with paper towels to remove amine blush, sand using abranet 80 grit with extraction. Suck off dust, wipe with paper towel, last couple of times using a solvent to try and get rid of the problem.

I have tried using chesnut lacquer thinner to clean straight before epoxy application.

Does anyone have any idea what could be a cause based on my pictures?

In some it looks like there is a tiny particle at the centre but its pretty hard to really see. When there's no light shining the pit just looks dry like there no finish.

When I apply the epoxy at first it's fine then as it cures they develop.

 

[Trainee neophyte]

I didn't know the answer to this, so went googling:

Fish eyes are where a coating pulls away from the underlying surface creating 'holes' or craters in the topcoat that go down to the bottom coating. They sometimes happen under certain conditions with epoxies. Two part polys (LPU) coatings are especially sensitive to fish eyes. Almost always they are caused by surface contamination, oil or wax, even in minute amounts.

And slightly more technical:

Why Fish Eyes develop in an Epoxy or Polyurethane Coating?
Why Fish Eyes develop in an Epoxy or Polyurethane Coating?
When a coating is applied to a substrate that is contaminated with low surface energy particles such as oil, wax, grease, or silicone, fish eyes may develop in the coating as it is applied. These fish eyes are produced because the coating is unable to wet out the contaminated area.

All substrates have a surface energy and as a general rule, adhesion is achieved when the surface energy of the substrate is 8-10 dynes/cm greater than the surface tension of the liquid being applied to the substrate. Epoxy and polyurethane coatings may have a surface tension in the range of 38 dynes/cm.

So, applying this coating to a substrate that has a surface energy equal to or greater than 46 dynes/cm should wet out and provide a satisfactory bond. Many waxes and polishes contain silicone which has a surface energy of 24 dynes/cm. If the surface cleaning of the substrate leaves behind these polishing contaminates, the coating with a higher surface tension will not wet out these low surface energy particles leaving behind fish eyes as a result.

This is why low surface energy polymers such as polypropylene (30 dynes/cm), natural rubber (24 dynes/cm) and Teflon (20 dynes/cm) are difficult to bond to as coatings typically do not have surface tensions low enough to wet out these substrates.

Many automotive manufacturing plants will not allow silicone based products in their plants, because silicone contamination is difficult and almost impossible to remove and control. A very small quantity of silicone in sanding dust or in a cleaning rag can contaminate a surface being prepared for coating/bonding.

To fix it:

https://www.swaylocks.com/forums/how-to-fix-fish-eye
If the epoxy is already cured, I just wipe the spots clean with denatured alcohol and the gently brush on a little more epoxy. Then sand out the high spots when I sand out the rest of the board....

...
A great trick I learned on this forum: usually a fish eye starts to form almost immediately after you brush on the resin. If you see one forming, take a clean piece of paper towel and wipe the resin off that spot -usually you'll also wipe off whatever the contaminate is so when you brush resin back over that spot it will lay down real nice.

Hopefully someone with real-world knowledge will be along to put us both straight.

 

[Rich C]

Interesting paper:
https://scielo.conicyt.cl/scielo.php?sc ... 8000300443

Wood has a varying surface energy depending on how it is prepared. Sawn oak in their study had a surface energy in the range 40-41 dyne/cm, which is similar to that of epoxy. Sanded oak had a much higher surface energy, in the range 52-55 dyne/cm.
That means if you have a spot that's not quite as well prepped as another, you could end up with a fisheye even without an contamination.

 

[Jonathan S]

Have you tried putting in less hardener?

Sent from my SM-J530F using Tapatalk

 

[Droogs]

9 times out of 10 I've found it is usually due to silicon in some form contaminating the surface. Paints much more susceptible than epoxy in my experience. Worst case I had took me 3 days to figure out why I kept getting the odd fisheye on a piece. Turned out to be the non slip mat on the bench was the cause by transfering silicon from it to my hand and then to the surface when I was picking it up to move the piece :roll:

 

[Keith 66]

The resin to hardener ratio with 207 is fixed at 3:1 you must not alter this either way or insufficient cure will result, Fish eyes like this can be caused by silicone contamination or amine blush, I have dealt with amine blush a few times & soap & water Is not really up to it. However the photos look like it could be an out gassing issue to me? I have seen this quite a lot on boats, its where you coat a surface then turn the heaters up & air in the pores of the timber expands & pop you have a bubble or bubbles, it bursts & then you have a crater that doesnt flow back, Heat surface first & try & keep temperature constant.

 

[Tetsuaiga]

Thanks for all your replies.

I'm now measuring by weight with some new scales that are .1gram accurate. So ratio shouldn't be an issue.

I dont think it can be outgassing as this is my bejng applied over a surface that's already been epoxied and sanded down.

I think contamination must be the issue, I'm struggling to identify it. I had some quite bad amine blush on earlier coats and did read it can still cause problems even after removing. That was 206 slow hardener now im using 207 which is low blush. I should have started with 207 really but didn't as I thought it was a bit softer, think ive changed my mind in that now though anyway.

Its interesting you mention grip material. I've been using 4 pucks from axminster which are some of rubber material, I'll make sure to stopbusong those.

I might have used one of the rolls of grip material too, the cross type one. I have always noticed if I put recently finished but dry material on that roll it would leave a pattern which needed removing.

I think next I'll try with no plastic/rubber type aids and also be careful what I'm touching as it's fairly likely I could have been touching the rubber then putting my hands on the wood.

I can also try adding some extra after say an 45 minutes curing to any spots I have.

I did use silicon lubricant spray on a lathe tool but this is all outside my shop, however the tools and pieces came back but have just been sitting in a box for months.

I wondered if it could be graphite from a pencil as I used that to check where I was sanding, i did a test yesterday with a heavily marked piece and there wasn't any problem with the epoxy adhering but ill stop doing this anyway.

It's very mysterious, only other thing i could perhaps improve is raiaing temperatue.

I'll try and let you know how it goes.

 

[rafezetter]

I was going to ask if this was new raw wood or over a previous finish, but you've answered that above.

If you are applying over epoxy (or other finish), it could be that the new solvent is affecting areas where the old solvent hasn't fully flashed off, is reactivating, and is causing the fisheyes.

This can happen even if the new epoxy and the old epoxy are the same brand, because if the old stuff is older than a year or two, formulations can change.

Also, have you been adding any extra thinner to the mix you've been using? More thinner = more application open time but also a higher risk of the underlying solvents in the previous layer reactivating.

This was basically the answer I got from Rustins when I had a similar issue with fisheyes using thier "plastic coating" which is a paintable resin.

They suggested sanding back and using a heavy duty degreaser used in the auto industry, then applying a thinner coat (thickness) which will have less solvent sitting in any one localised area, reducing the risk of it reactiviating the underlying layer.

If that goes off ok without fisheyes, then you're good from then on.

Fisheyes are a PITA, hope you get it sorted.

 

[Tetsuaiga]

Thanks, me too.

Nope I didn't thin it. I warmed the epoxy a bit before mixing them, as well as the room. Probably about 19 to 20c as I did have a thermometer to check I wasn't under 16c which is outside their recommended range.

Hm I might look into decrgeased or I think west do a solvent cleaner of their own which should obviously not have compatibility issues.

I'm fairly sure the solvent had flashed off but actually I didn't give it a lot of time, perhaps some could be there even though I couldnt see. This is another change to make.

West epoxy is supposed to have extremely high solids, I'm not sure what other epoxies contain to make them thinner but west is meant to be very low.

Interesting tip about just a very thin coat.