Troubleshooting Fisheyes

The dreaded fish-eye rears its ugly head again, and pros provide systematic troubleshooting tips to identify the source of the contamination. August 9, 2005

I've been using Enduro polyurethane for about three years without much trouble. Yesterday I sprayed two coats of sanding sealer and sanded the first one. Today I sprayed a coat of satin poly (with amber overprint) and it's a mess. The finish pulls back and leaves holes all over the piece. The holes are probably 1/4" or so in diameter and they're everywhere. Called Compliant and, as usual, anyone who knows anything is at a trade show. The fellow who answered told me to get the temp up from 65 degrees to 70 degrees. I did this and the problem seemed to get worse. I thought maybe the stuff was too old (about two years - three gallons left in a five gallon bucket). The Compliant guy said he thought it was okay. I tried some other Enduro without the overprint that I've had about the same length of time and it worked on some pieces but pockmarked others. This stuff has to be sprayed tomorrow and I'm at a loss for what to try. Any ideas would be appreciated. Also any recommendations for a brand of water-based poly. It's a real pain when nobody's there to help with problems.

Forum Responses
(Finishing Forum)
Fisheyes = contamination. You might have a surface contamination problem such as stearates from the sandpaper, oily tack clothes or a contaminated air supply for your spray gun. Also, and I have had this happen to me with other water-based products, the material may have just gone bad over time. The good people at Target Coatings instructed me many years ago when I started using water-based products in the boatbuilding trades that some formulations last longer than others. You first need to backtrack your procedures to ensure that you are not contaminating the surface or the finish. I realize that this is a frustrating problem but you need to find the source of the problem, with or without the Compliant vendor. You might have an easy fix. That said, give Jeff Weiss at Target Coatings a call. He and his staff will help you out, regardless of whose product you are working with. They are smart, easy to work with people.

Sounds like fisheye to me. If it looks like craters on the moon, that's what you've got. Usually this is caused by silicone contamination in the wood and your finish is pulling it up and trying to mix with it. You can try sealing it in: sand back the craters as best and as flat as you can, then seal with shellac. The Zinsser spray cans from the hardware store will work. Don't sand the shellac after it is dry. Spray a coat or two of your finish on top of the shellac before you do any more sanding. This often works but not always. You can strip and start over, using the shellac as above after staining. I use ML Cambell's Ultrastar (water borne) and they offer a WR-4 fish eye reducer additive (which is silicone based), however I rarely use this and I consider it a last resort.

From the original questioner:
Thanks for the fast responses. I don't use stearated sandpaper and there's no silicone in the shop. I thought maybe the plywood was factory sanded with stearated paper but the problem is on lumber, too, although not as bad. The screwy thing is: the sanding sealer went on just fine - two coats. Does kind of look like a contamination problem, though, doesn't it? Thanks for the help. I'll give Target a call.

Before you waste a lot of time backtracking, it's worth a check to see if it's the product. Apply one coat of the Enduro with a clean brush to a clean glass surface. (Clean with denatured alcohol or acetone and let dry.) Apply at least two coats of the product. Sand half of the glass surface after the first coat with your sandpaper. Leave the other half unsanded. With the application of the second coat, you can determine if the product is bad. If the problem happens only on the side that was sanded, it's your paper. If neither side has the problem, then it may be your air supply. If you're using compressed air, prepare another glass panel and using a blow gun, blow air over half of the surface (mask off the other half). Apply your finish and if the contamination shows up on the side you blew air on, then it's your air supply.

From the original questioner:
Your testing method is intriguing. I checked my air filter and it looks clean. But I brush-painted some finish and it didn't crater - same plywood. I'm wondering if it's gun-lube that's contaminating things. I might be spreading it around too much. I'll try cleaning the poop out of the gun and not lubing it. Thanks for your help. This is a great site.

From the original questioner:
That was it - gun lube. I cleaned the gun with lacquer thinner, rinsed with water - problem gone. Thanks again!