I am refinishing a coffee table that has been in the family for about 40 + years. I think the finish was shellac but I am not sure. Anyway I sanded with 320 wet dry and mineral spirits down to the wood as close as I could without sanding through the stain. Cleaned it real good with mineral spirits, let it dry and applied a coat of wipe-on poly, made with 2 parts minwax poly and 1 part mineral spirits. As it dried, small spots appeared. It appeared as if the varnish, for some reason, would not cover these spots. I’ve seen pictures of “fish-eye” and it doesn’t seem to be exactly like that. I’ve attached some pictures. Does anyone have any ideas of what is happening?
I sanded and cleaned and applied another coat and they appeared again but in exactly the same location nor were the spots of the same size.
Replies
Poly and wax or oil are not happy together. Sand lightly and put down a barrier coat of dewaxed shellac or Zinsser Seal Coat. 1 pound cut. Just needs to be very light. Don't sand that. Any finish you want works on top.
Frank ,
It does have the cratered fish eye look to me. When refinishing this is a fairly common thing especially since you did not use a chemical stripper , silicones and a or wax and others from the old finish may be what is causing this effect. When using spray lacquer I generally would add smoothie or another type of fisheye remover , when this happens .
good luck dusty
Same location but smaller spots with the second coat? It looks and sounds like fisheye to me.
It sounds like you've got a contaminate of some sort. But I think thinning the poly with the Mineral Spirits made it worse because that made the finish thinner. Too thin of a finish is a known cause of fisheye, even without the presence of any contamination which is the usual culprit. And it'll do it sometimes in areas where you'd never have had any problem with a thicker finish. It's basically a function of the surface tension of the liquid finish. When it's thin it has less surface tension as a liquid and that leaves it vulnerable to pulling away from from a spot at the slightest provocation. I've ran into it before with over-thinned lacquer years ago. I thought I had contaminents, but it turned out to just be the over-thinned lacquer that was the culprit.
The shellac suggestion is a good one. It should work. It'll bridge the problem areas and then the thinned poly will flow out just fine.
For future reference, when you run into fisheye like that, try to bridge it with very thin coats and let them dry before applying another coat. Flooding a fisheyed surface with a lot of finish will not help to bridge the fisheye... Again, because of surface tension.
In the automotive refinish industry they spray on really light mist coats over fisheyes until they bridge it. Letting each coat flash off thoroughly. Once it's bridged you can lay on the finish really heavy without the fisheye coming back. DuPont even teaches this fix in their manuals. I expect that their competitors do the same. Even though you're brushing poly, the same principles still apply. Thin coats allowed to flash off completely inbetween coats will bridge fisheye.
"Rather fail with honor than succeed by fraud" - Sophocles.
As others have said, it is probably fisheye. You could do a quick coat of stripper to remove the small amount of finish you have on the piece. Be sure to remove all the stripper residue with mineral spirits. Do the barrier coat of shellac as was suggested and then apply your finish. Thinning the varnish with mineral spirits does not cause this--wiping on 50/50 varnish is a well known finishing technique.Gretchen
Thanks for your suggestions. I think I will do a quick strip of the table and apply a thin coat of dewaxed shellac. This is my first major finishing project and to be truthful I have been a little apprehensive. (My wife says I have delayed long enough and its time to get to work on it.) So, thanks for the help.
Frank
Frank,
There is a product you can add to varnish that eliminates fish eye problems. I wish I could remember exactly what it is called (I'm told the memory is the second thing to go...). I've seen it used, and it works great. You might try the good folks at Homestead, they may be able to help you.
Alan
Every fisheye remover or wetting agent I know about has silicones in it. Whether for lacquer, shellac, or varnish. Requires great care. Like putting out a fire with more fire. I don't recommend any of them for amateur use. Too little, they don't work. Too much, they don't work. All may cause future finishing problems. Shellac is easy and reliable.
Bob,
Then that wasn't what my friend used. He took the cap off the can, drizzled a bit in the paint bucket, considered it a moment, poured in some more, and said "That ought to do it."
I asked him what it ought to do. He said it was to take care of any "silicone infection." I saw him use it many times, he never measured or worried over it. It was obvious there was nothing critical about the amount added. He carefully measured things when it did matter.
He was extremely good at this stuff. So it's possible that he used some secret formula that he whipped up himself.
As I said, I don't remember too much about it.
Alan
The stuff sold as fisheye remover is a silicone compound. Normally used only in lacquer and shellac. For varnish I've rarely ever had such problems. Mineral spirits is a solvent for most silicone oils and waxes. I think it dissolves the stuff and lets it float to the top so there's less trouble with oil-based finishes. Water or alcohol generally don't dissolve waxes or silicones so they're more sensitive to the surface condition. Your friend may have been using Penetrol. Sort of a thinner/oil/dryer compound. Makes oil-based products spread easier and smoother. Inexpensive and you can use as much or as little as you want. Actual fisheye eliminator usually is used only a couple drops per gallon.
Bob,
I've seen Penetrol mentioned elsewhere, but I'm not familiar with it. What exactly is it? A thinner, oil, dryer, okay, but can its effects be duplicated with some mineral spirits and some Japan Drier?
Also, I've never seen shellac react to any surface contamination other than wax. It's easy to discover wax when I wipe down the piece prior to finishing because wax resists almost everything. What do you know that I don't? Does shellac react to silicone the same as varnish?
Alan
Penetrol is a "proprietary" additive. As best as I can figure, it is a long oil wiping varnish with flow and adhesion additives. It isn't the same as a thinner. It does not thin a varnish or oil paint nearly as much as an equal amount of thinner. It does make it level better and maybe increases the gloss a bit. I have actually used it as a wiping varnish many times with good results. I don't believe you can easily duplicate its performance with any simple homebrew formula. Its commonly used when spraying oil paints. Even a lot of the big box stores sell it near the paint sprayers. Most every good paint store carries it. The same manufacturer makes Floetrol, an equivalent product for latex. Sort of a thinner that doesn't thin. Does what a thinner would do, but doesn't change the viscosity as much. Not expensive. 6 bucks a quart in these parts.
Silicones are complicated. Look at the variety of hydrocarbon solvents and oils available. Lots. Take the carbon atoms and substitute with silicon. That's a silicone or more properly a silane. A huge variety of products. Some are soluble in ketones, which are the ones used as lacquer fisheye remover. Some very few are soluble in alcohol. Those are used for shellac. Most are soluble in other hydrocarbons. Silane oils and their unique driers are used as special purpose high temperature varnishes.
For the most part, shellac is about the best bonding agent there is. Usually even will bond to waxy or resinous surfaces pretty well. Natural shellac has a good percentage of wax in it already and it seems happy about bonding with a lot of waxes. But, it won't stick to the ketone-soluble silicones and some waxes.
You're right that thinned finish doesn't actually cause it. But it can exacerbate the problem by causing minute amounts of contaminate fisheyes to show up under conditions where they wouldn't show up at all if an un-thinned finish were used.
As I said, this is a known "cause." I first became aware of it about 20 years ago when I read it in a finish trouble shooting data sheet. It doesn't "cause" it per se. That's just the way most trouble shooting data sheets are layed out. Poor terminology, to be sure. But, it's still a valid point regardless of the terminology.
Preemptive Karma
"Rather fail with honor than succeed by fraud" - Sophocles.
But, it's still a valid point regardless of the terminology.
No, I don't think it is because you said it was caused by the thinning. That just isn't true. That is what I was objecting to. If there is fisheye contamination it may manifest itself with ANY finish. I think it is actually interesting that in 40 years of refinishing furniture I have never had any fisheye, but I have always used stripper.Gretchen
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