Fisheyes and Cleaning Between Coats

this time involving waterbased finishes on bamboo. October 26, 2007

I'm trying to finish caramelized bamboo with ML Campbell Utrastar and an HVLP system. I'm sanding to 150, blowing off dust with an air gun, and wiping surface with acetone. First coat is fine. I then sand with 320, blow and wipe with dry rag. After the second coat, I'm getting fisheyes, etc.

Should I be wiping the surface with a chemical (DN alcohol, naphtha) or is there a better way to get a good finish? I'm cleaning the gun in warm water only and it is only used for WB finishes. Any help with a good sequence for finishing here would be appreciated.

Forum Responses
(Finishing Forum)
From contributor D:
What kind of sandpaper are you using to sand between coats? If it is grey/silver stearated paper, that may be your problem. The stearates they use can cause fisheye with WB. You should use gold paper. I prefer 3M 216U paper, but there are others. I usually use either 400 or 600 grit.

You shouldn't use any chemicals to wipe off the sanding dust between coats - they can damage the finish. Use only a water-dampened rag.

From the original questioner:
Thanks for getting back to me. I'm using 3M 216u. My finish is covered in fisheyes. There were no fisheyes after first coat.

From contributor W:

Another possibility is that your compressed air is contaminated with oil. According to your procedure, the acetone would wash off the oil before the first coat, but not before the second. Also, you don't state whether you're using a turbine or not. If you are, the only source of the oil would be when you blow the pieces off prior to spraying. I would take a really close look at your shop air; maybe some good filters are called for.

From contributor D:
Well at least you've eliminated that. You are going to have to do more troubleshooting - is it the wood, gun, or finish?

Sometimes WB will look fisheyed as if from contamination, when really it is just the finish not flowing into the pores of the wood - a surface tension issue.

Have you had this problem with anything else using the same finish or the same batch of finish? If you haven't used this batch, you may want to try it on another species of wood, preferably a smooth one like maple or cherry. If it fisheyes then, you know the problem isn't just with the bamboo. If you are using a turbine, then you can rule out oil from a compressor.

Another thing you could do is seal the bamboo first with some dewaxed shellac and spray your WB over that. If there is any contamination in the wood, that should seal it off. Alternatively you could scuff what you've already done and seal that with dewaxed shellac. You could also wipe down your raw wood with acetone and/or alcohol before you seal with the WB to remove any contamination. Or you could try to bull your way through it by scuff-sanding out the fisheyes and applying your WB. A lot depends on where you are in the project and how much time you want to invest, but I would probably want to: 1) try the Ultrastar on a different species of wood using the same methods you are using on the bamboo; 2) strip off what you've done with acetone or lacquer thinner, seal with dewaxed shellac and coat, or 3) bull your way through it by sanding back and trying to overcome that fisheye, if it is not from contamination but just the nature of the wood.

From contributor J:
Another quick way to test your coatings for fisheye issues is to spray it on glass. It needs to be cleaned very well. I usually use acetone as my final cleaner. Spray your coating on and watch it. If you have fisheyes, then you have a problem with either your air or your coating. If you have nothing, then it has something to do with what you did before.

From contributor B:
Another reason is that Ultrastar just sometimes does that. With us it was always on the third coat, though. Switch over to the Agualente. It's far superior to the Ultrastar, and I've yet to have one problem with it of any kind.

From the original questioner:
Thanks for the heads up on air. I did check filters and the oil filter is old and has some contaminants in there. I do have Dominick Hunter filters and they are very good, but I need to replace them. If oil is the problem, is there a solution that I could wipe finished surface with without damaging finish, like a DN alcohol or naphtha? This is killing me, as I need to get this finished by tomorrow.

From contributor D:
Naphtha, maybe. But might there not still be oil in the hose going to the gun?

From contributor P:
Try straining the finish and thinning it 15% with water. Don't wipe the sanded first coat with a solvent. Either you will damage the first coat (acetone) or leave an oily residue (naphtha).

From the original questioner:
I have an oil-less compressor that I'm going to use. It would seem that it's oil from the compressor. I'll post back with results.

From contributor P:
If you have contamination in the airline, why doesn't it affect the first coat?

From the original questioner:
I'm wiping bare wood prior to first coat with acetone, hence no fisheyes. I've just resanded down to bare wood again. Will try oil-less compressor and see what happens.

From contributor P:
I understand the wipe down before spraying - that will remove surface contamination on the wood. But if oil is in the airline and traveling through the spray gun, it would cause fisheye on the first coat as well. One scenario that makes sense is that there is oil in the airline, and when you blow the piece off, that's when you're getting oil on the surface. That's only in the case that the air you use to blow the piece off is not filtered as well as the air going through the spray gun.

I have had success preventing fisheye with WB finishes by filtering the finish through a cone filter, then thinning it with water, and spraying very thin coat(s). Applying a heavy wet coat makes the problem worse.

When you do get surface defects, you can sand the finish back and recoat without starting over from scratch. It may take a few recoats with sanding in between if the defects are bad, but it's often easier than going back to bare wood. Especially if you've stained the wood or used a glaze in the steps.

From contributor D:
I don't think naphtha will leave an oily residue. It's a pretty good degreaser. I would be hesitant about using it on non-cured WB anyway, though, because it's pretty strong and would likely affect the finish.

From contributor A:
I use Ultrastar and Polystar regularly, and have seen the same problem many times. I am 99.9% sure it's not caused by any kind of contamination. Campbell is aware of the problem, and they can't explain it, either, other than to say that the product is sensitive to temp and humidity.

Like you, it's usually on second or later coats. I suspect it's a surface tension problem. It seems more likely to happen when the first coat has had a longer time to dry. Maybe some component of the product coming to the surface as it cures? It also seems more likely to occur when I spray older product (shelf life problem).

The best advice is to spray one panel (or door) and wait to see what happens before you spray the rest of the job. Strangely, this is the *only* WB product that gives me this problem, and I continue to use it.

From contributor P:
Naphtha isn't as oily as lower distillates, but the water-base finish manufacturer I've dealt with the most (Target) warns against using it or other petroleum distillates between coats.

From contributor D:
Interesting. I've never used it between coats of WB and can't think of a situation where I would, but I thought naphtha would completely evaporate. Anyway, thanks for mentioning that.

Oh, wait, I did use it once after I had rubbed out a top with steel wool and then felt I needed to put on another coat of WB. I used it to take off any oil residue left from the steel wool. Didn't have a problem that time, but I wouldn't make a habit of it.

From contributor G:
Try vacuuming the surface clean. I use my shop vac with a fine brush attachment. Keeps dust out of the air also.

From contributor I:
Don't use naphtha, acetone, lacquer thinner or any other solvent to clean your surface. Use a wax and grease remover made for auto refinishing. It's cheap and is made for cleaning before spraying. A lot of auto parts stores like AutoZone carry it in a spray can. All those other solvents do leave residues. I also use Endust on a clean rag for tacking off the dust. It works better than a tack rag and never interferes with the finish. I've been painting cars and finishing cabinets for the last 10 years with it and never had a problem. If using Endust makes you nervous, then use a tack rag that's designed for auto refinishing. They're readily available from paint stores. Also, the rags you're wiping with may be your problem. Make sure they're clean and washed with no fabric softener.

From contributor R:
I agree it's an Ultrastar problem. As great as this finish is, it is finicky once in a while. I believe the first coat levels fine, but while it is wet it pulls some kind of contamination up out of the wood. This then causes the cratering in the second and subsequent coats. If you sand the craters out of the first coat and seal with shellac, this usually solves the problem. This didn't happen often with Ultrastar and it seems to come out of nowhere. I switched to General Finishes High Performance about 18 months ago and haven't seen a crater since.

From contributor A:
Contributor I, the questioner is having problems with a waterbased product. The wax and grease removers and tack rags you mention are for solvent based finishes, and will almost certainly cause problems with waterbased finishes.

From contributor C:
Crystalac surface conditioner. Made for WB finishes.

From contributor Y:
I have had that problem with Polystar also. I would do as stated above and use a shellac seal coat barrier and then put Aqualente over it.