I just tried doing a gloss coat of epoxy on both sides of a board and I had a serious problem with ‘cratering’ or ‘fish eyes’. I have had the problem a couple of times before on a small scale, contamination along a pinline, and am trying to track down the source of the contamination this time. (it covers all of the board)
My suspicion is a pair of gloves (rubber dishwash kind from a dollar store…) that I used to handle and wash down (alcohol) the board after sanding. I think I might have used a pair of gloves (there are several pair lying around… seperated now…) that I had used to clean up my shop fridge with some strong cleaner; and that probably left the contaminant behind.
However I just wanted to make sure of something. It is also the first time that I used a certain kind of sandpaper. I am using a 5" random orbital, and for a while just bought small packages of red colored discs, but I recently went to home depot and bought large packages of yellow colored discs. On the back of the package it says that the discs are coated to prevent loading, but that they won’t leave any residue. Can that statement be fully trusted if applied to epoxy resin?
Is there any chance that they actually are leaving some kind of residue behind?
I have gotten rid of the possible gloves culprits, but would like to know of any experience with sanding discs in case they might be the cause BEFORE I do the next gloss coat.
Yes, it was the stearated discs. They are great for woodworking (I use them in that capacity), but I had the same experience as you did with epoxy before I found out the hard way. Get a box of nitrile or latex (if you are not allergic) gloves, so you don’t have to worry about cleaning them, just throw them away after each use.
For sanding hotcoats, you just want regular aluminum oxide sandpaper. I have found that it is sometimes hard to tell, but if a brand says no clog or less clogging, it is a good bet that it is stearated.
When it happened to me, I just sanded the messed up gloss down and glossed again. To keep track of your sanding progress, put some sharpie marks in the fisheyes. When those marks are almost gone, you are close to being done. This may mean you will sand off some of our graphics…
Do not contaminate the wood or film surface with oils of any type. These oils will cause a small circular dimple in the surface film, called a "<span style="font-weight:bold">fisheye</span>." To insure a clean surface, do not use <span style="font-weight:bold">sandpaper</span> that has anything added to its surface for easier sanding.
wiped the board down with alcohol before appling resin
There’s a strong possibilty that when you wiped the board down you spread the contamination all around. Lot’s of people on Swaylock’s recommend skipping this step. It also sounds like you work space needs to be a little bit cleaner and more organized. Maybe there’s lots of stuff floating around in the air from all the other stuff you do in your work shop. Oil ,grease, solvents, tire dressing, spray cleaners ,ect.
For me gloves and brushes are one time use. Mixing cups and buckets one time use. Tools used for glassing are not used for anything else. I still have some problems but no body’s perfect.
One more thing…Resin is a strange animal. Some times when I try to spread it too thin I have problems but if I keep it thick everything flows out better
I suspect alot of contaminants are actually due to the alcohol people use, most of the time the alcohol you buy is not 100%, it often has water and sometimes other things added. Check the label.
But dust and moisture anything really will give epoxy an excuse to fisheye… heated resin seems to have a little less trouble than room temperature resin in my experience.
I wonder if it’s possible to do a finish coat in the vac bag? Anyone try that? I’ve noticed that if your plastic is really tight you get a nice crisp and shiny surface…
Yes to everything stated above, and I’ll make one addition:
If you start to see fisheyes appearing on the board, there is a way to help minimize the damage. Assuming you have a bit of resin left over in your container: as the resin starts to thicken up, take a stick dipped into the thickening resin and apply a drop or two to each crater. The thicker the resin, the better…so it won’t spread out or crater again. Timing is everything. The goal is to turn the crater into a little “mound” that can be sanded out. I’ve saved hours of time with this method, avoiding the BIG sand down of the whole layer of resin.
And to reinterate:
Don’t blow off with compressed air. Any oil-lubricated compressor can let small amounts of oil through.
Wipe down with alcohol using paper towels, not cloth. Detergents, fabric softeners, etc. may be present in cloth rags.
A pre-wipedown with a commercial painter’s tack cloth is good for removing dust particles. It won’t affect either poly or epoxy resin.
Always think of what may be getting onto the surface from other sources, and try to avoid it. Clean is the byword.
Doug
P.S. The above method can also be used after the resin has set. Just rough up the crater with 100 grit sandpaper for adhesion, and drop in the new resin. Wait til it hardens, then sand. It beats sanding down the whole board.
I haven’t done a ton of epoxy boards by any means, but i haven’t had any problems with what your seeing. I do take a few preliminary steps to make sure i don’t get any cratering or what not. I do the samething for my poly boards too. 1) I only touch the blank after shaping with paper towels between me and the board. 2) I only laminate when it’s warm. 3) I handle the laminated blank with waxpaper between me and the board. 4) Once the board in hot coated, I only sand it to 100 before I gloss. I also wash the board off with water, nothing more…just water and a clean cloth.
DNA, Dish soap, hand lotion, simple green, agent orange, etc can all leave a residue. If you sand it clean, and expose clean resin you should be good to go. I use all sorts of sandpaper, I’ve used the Home depot stuff, the red, the yellow, I’ve used Harbor Freight is all the same… It all sucks until you cut the shine off the resin / epoxy, once you do that it sands like butter.
it was those meat chop hands of yours, stuffed into those filty Playtex gloves. What did you expect?
Don’t touch the blank, don’t touch the lamination,…don’t touch the fresh sand out. And you’ll never have any problems. I just love it when the UPS guy rubs his hands over the rails of a freshly finished blank." he dude, one of these days i want you to make me one of these" Yeah, and i’ll make sure I put a couple of finger prints right on the deck nose.
