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No, not the song, but uke related.

I'm spraying some varnish (my first time using varnish) on my ukulele, and am having issues with tiny pinholes in the finish. Not sure if they are air, or surface contamination, or what. (Never had this trouble with waterbornes...)

I'm sanding between coats with 3M fold paper (good stuff) and then wiping it down with naphtha prior to spraying. I also go lightly with a tack cloth just prior to spraying to get off any dust which may have settled there.

I have one of those small plastic filters right at the gun, and a water filter in the line on the other end of the hose.

Any thoughts as to what causes these things? What do I need to do to fix this...get a better gun, adjust my pressure, get better filters, hire an exorcist?

Thanks.

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"I want to know what kind of pickups Vince Gill uses in his Tele, because if I had those, as good of a player as I am, I'm sure I could make it sound like that.
Only badly."

When do the holes form? As soon a you spray or do they show up as the coating dries? Did you use any type of sealer? what about pore fill?

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Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

Pores were filled with shellac and pumice three weeks ago. It was sealed with SealCoat a a couple weeks ago. The tiny bubbles did not show up in the first coat, but began showing up in subsequent coats. Second coat went on 48 hours after first, and each coat went on at least 24 hours after the previous coat, after sanding with 600 grit and cleaning with naphtha and wiping with Crystal Premium tack cloth.
I guess it could be pore filler failure, but it was covered up long ago by a few coats of varnish...so I'm reluctant to think it could be gassing off still. I'm no expert, so perhaps that's the deal. Doubtful though in my mind.

After spraying, I'm emptying out the leftover varnish from the cup, and running thinner through the gun (sprayed), and then thinner sits in there all night and day until that gets emptied out and the remainder gets sprayed out until only air comes through the gun, then I start with the varnish mix again.
I'm careful not to leave the lid off the jar or the gun cup, so opportunity for contamination that way is highly limited.

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"I want to know what kind of pickups Vince Gill uses in his Tele, because if I had those, as good of a player as I am, I'm sure I could make it sound like that.
Only badly."

My first suspicion also is pore fill, but the first coat of varnish went on without issue so I kind of doubt that is the case. If the bubbles show up directly after being sprayed the problem is likely some type of contamination, if they start to appear as the coating flashes it is a thinner or film problem. I have in the past had issues that I traced back to a tack cloth, did you use the tack cloth between the sealcoat and the first coat of varnish?

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Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

I am not sure it applies to varnish, but trapped bubbles in lacquer are caused by spraying too-heavy coats.

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John

I'll attest to that. In the process of stripping a back down now to remedy. Whatever the source of your troubles, I feel your pain.

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Aaron Craig

John, too thick a build, or too thick a mix? This of course is varnish, not lacquer but it seems like there must be some similarities.

The crazy thing is that the first coat was thicker than the rest, both in build and in ratio of varnish to accelerator and thinner. After that, I added more thinner and some acetone to the mix per someone's instructions. None of that should have been an issue. The last coat was sprayed on thinner in build, but back to the 1:1:1: ratio as prescribed by the manufacturer, so a thicker mix - and it still had pin holes, but perhaps not as many. They didn't form over time, they were just there. I bought some new disposable filters for the gun today (the kind that attach in-line with the gun and hose) and see if that helps. Perhaps it's moisture, but who knows. I suppose the gun itself could be to blame even. It's a Walcom STM HVLP gun, 1.2 tip. Perhaps there's too much air in the mix, and the viscosity of the varnish just holds onto the air.

I guess I will eliminate two of the possible variables for the next coat - changing out the filter, and not using the tack cloth. I will report back with results if folks are interested.

Thanks,

Don

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"I want to know what kind of pickups Vince Gill uses in his Tele, because if I had those, as good of a player as I am, I'm sure I could make it sound like that.
Only badly."

Coats applied too heavily/too thick a built each coat, almost to of at the point of running. With Nitro, under the right circumstances, the thinner flashes off from the surface of the coat, trapping solvent below the hardened surface, which, though wonderfully hidden until about the time you go to buff the finish, later appears as a million tiny freakin pin holes from hell that don't like to sand out (though they will if you can get below the problematic layer before sanding through).

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Aaron Craig

Yeah, so I guess it also remains to be seen if the pin holes are actually in the fresh coat, or showing through from a previous coat. Good point. I'm not sure now. Dang, I'd hate to have to sand it all back and re-stain the yellow top. Ugh.

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"I want to know what kind of pickups Vince Gill uses in his Tele, because if I had those, as good of a player as I am, I'm sure I could make it sound like that.
Only badly."

Most Varnishes cure slowly enough so that trapped solvent isn't usually a problem. Re coating too soon will give you problems when you try to level sand and buff, but I've never seen pin holes from it(with varnish). I suspect you need cleaner, better filtered air. I always had a "standard" water trap at my compressor, another in my booth, and one of the little inline filters at my gun........but occasionally had problems. I got a big 3 stage desiccant filter a year or so ago and haven't had any problems since. The filter I have is the first one on this page. http://www.tcpglobal.com/spraygundepot/daircontl.aspx#TheBigOne I believe the problem is compounded when you have an oil lubed compressor. (both of mine are oil lubed). The tiny droplets of water, or oil will cause small craters in the finish.

IME the Walcom STM is a good gun. I use a Walcom EGO (which is a little smaller) with a 1.2 tip for Varnish as well as Polyester. I've used it for lacquer too.(and automotive urethane on motorcycle tanks)

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I didn't mean to say it, but I meant what I said.
http://www.brackettinstruments.com/

What was the original finishing environment?

This sounds like trapped finish outgassing to me.

Environment : My shop, 40-45% RH, temp in the 70's. Fairly dusty environment but I run the air filter for awhile before spraying.
Varnish is Epifanes Gloss varnish, with accelerator and thinner all by Epifanes.

Woody, that unit looks pretty good, and for a very reasonable amount of money. I'm going to see if the local spray shops in the area have one in stock. If they do, I'll get one today and install it. I have a basic water trap at the beginning of the hose connection, but perhaps it's not enough.

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"I want to know what kind of pickups Vince Gill uses in his Tele, because if I had those, as good of a player as I am, I'm sure I could make it sound like that.
Only badly."

From Epifanes;

Question: I am experiencing air bubbles drying in my varnish.

Answer: We will bet that what you are experiencing is dust. Dust and/or lint particles that dry in the varnish can form tiny craters that can certainly look like air bubbles. It is very rare for air to dry in a coat of varnish. Let's try to figure out where this dust might be coming from. If the coat looks great upon completion but several hours’ later looks as if someone has taken a saltshaker to your boat, then the dust problem is most likely airborne. If the dust occurs right away, brushes and the initial cleanliness of the surface are more likely to be the culprits. Here are a few, sometimes overlooked, sources of dust; • Although your brush may appear clean, try flicking the bristles in front of a bright lamp. You will be amazed at what comes out of it. Turn on the TV and be patient. It can take an hour. Do not assume that a new brush is clean, new brushes are particularly dusty. • Be aware of what is happening overhead, it may be that your basement ceiling is shedding dust each time someone crosses the room upstairs. • Fluorescent lights will act as a dust magnet until the moment you turn them off. • Check your clothing. Wear dampened Tyvek coveralls. • Mask or temporarily seal all screw holes. Your brush will certainly pull out whatever is hiding in those holes. We know a painter that varnishes in the nude listening to Vivaldi. Hey, whatever works.

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Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

Brian, I am not the least convinced that it isn't dust. I have enough dust in my shop for several shops. It could very well be. That said, I've been pretty careful to make sure there's nothing on the instrument prior to spraying (not brushing). I'm running the air filter prior to spraying, and the air shows no signs of dust when I spray. I don't have any flourescent lights in my shop, they are all Halogen track lights. The bubbles show up immediately, so if it's dust, it's somehow settling on the instrument between the time I clean it and the time I spray. It's possible. Their response also doesn't seem to be geared toward spraying or using accelerator. Dust...yeah it wouldn't surprise me. Some of it definitely is dust, but that usually shows up as a bump, not a pi hole.

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"I want to know what kind of pickups Vince Gill uses in his Tele, because if I had those, as good of a player as I am, I'm sure I could make it sound like that.
Only badly."

You said you wipe inbetween coats. You might be contaminating the surface doing that. Dusty rag or cheese cloth. Just something to check. Some cheese cloth has stuff in it to help pick up dust. I like plain old linen for wipeing down between coats as it doesn't leave anything.

I wipe using a microfiber cloth with naphtha to remove any oil or grease. I then use a high quality fresh tack cloth to remove dust particles. The tack cloth is the last thing to touch the wood prior to the spraying.

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"I want to know what kind of pickups Vince Gill uses in his Tele, because if I had those, as good of a player as I am, I'm sure I could make it sound like that.
Only badly."

That tells me it is some type of contamination, but where from? I agree I have never seen dust leave holes, only nubs. It could be oil or water in the air supply or gun lube. Did you spray any out on something else? I always have a panel in my booth to shoot test patterns on to aid in gun set up and to help diagnose problems like this. I have had problems with tack clothes when using tung oil in the past and as a result now rarely use them any more.

_________________
Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

the only time I've seen bubbles show up immediately was when my HVLP gun needed to be rebuilt...it was allowing air to get into the fluid flow before atomization...the clinker was that it was a brand new gun...drove me rather crazy as one would think a brand new gun would operate correctly...

also with varnishes it is typical technique to try and avoid any agitation of the product because of bubble issues during application...perhaps waiting a bit after mixing in reducer would help...

as far as tack cloths I've found one needs to only very lightly drag it across the surface...pushing hard will likely transfer some of the tacky substance to your project

as noted in the previous post, test panels are a very good idea for various reasons...after a project I like to use the test panel to see just what makes the finish fail...in my book the finish should properly resist damage from my thumbnail (i.e. be scratched by not peeled off) and decently flow around a hammer impact as opposed to flaking off in chunks...

Dust and bubbles look very different. It's obvious if you look at them with a magnifying glass. Bubbles will show up as white pin hole spots when the varnish is sanded back.

It might be bubbles. As has been pointed out, this will happen when spraying lacquer if the coats are too thick. The obvious thing is to adjust your technique as well as the mix and/or pressure on your gun to get a thinner coat. I've not tried spraying varnish as the advantages are not immediately obvious to me.

On rare occasions, I have gotten bubbles in rockhard varnish, but not while spraying. This seemingly was due to the varnish flashing off quickly because of warm weather, combined with rushed technique and a cheap brush.

At any rate, if it is bubbles, it's probably related to the top flashing before the bubbles escape, same as with lacquer. You may want to back off on the accelerator, and/or add some turpentine or other retarder to the mix, to give the bubbles some time to escape.

Either one. A thicker mix is more susceptible, since it usually results in thicker coats.
I have never heard of putting acetone in varnish, but I am not a varnish user.
It seems to me that acetone would be a possible cause, since it flashes off so quickly.
By any chance....are you shaking the mixture? I know that will cause bubbles in lacquer.

_________________
John

Hair dryer will lift up bubbles.

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Jason Moe
LaCrosse WI 54601

Don, it's so hard to help diagnose this online, but I'm kinda feeling like Mike that there's an air problem in the equation.
I was getting tiny air bubbles in my lacquer (Cardinal), which was technique related.
Addam Stark told me to back the gun further away from the surface of the instrument.
It drives me crazy, but it works.
I'm sure the variables between my lacquer and your varnish are legion, but it sounds like something going on with the fluid/air ratio. Or the distance, or the viscosity, or pressure, or...

Someone suggested panels. Good idea to experiment. Perhaps cut the pressure back on your compressor?

Best of luck,

Steve

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From Nacogdoches...the oldest town in Texas.

http://www.stephenkinnaird.com

Steve, I think you're on the right track. I was noticing that I didn't have the normal wide pattern in the spray that I was used to, somehow since the last time I used the gun (a couple years back) the spray pattern knob had been turned so it was more of a spot than a line, if that makes sense. The next coat will get a normal pattern prior to shooting, and from a bigger distance. The pressure is set at the compressor at around 34-40 psi, and then gun throttles it down even further. I may drop that pressure down a little more at the compressor to see what happens.
I also bought the filter that Woody recommended, and will get that installed soon. Hopefully all this will help. I paid a little more for it, but I guess I'm supporting the local economy.

Edit: The pressure was a good bit higher at the compressor prior to yesterday's coat. I lowered that pressure down to 35-40 and replaced the disposable air filter prior to spraying. I had less bubbles, but still some dust. Definitely need a clean spray booth area. I guess that means I need to hit the lottery...

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"I want to know what kind of pickups Vince Gill uses in his Tele, because if I had those, as good of a player as I am, I'm sure I could make it sound like that.
Only badly."

FWIW...

I just checked yesterday's coat, and it looks much better than prior coats.
And I have to say, this finish is stunning... it has even more "Wow!" factor than any nitro finish I've ever seen. I won't even have to buff out the neck, it's that nice.

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"I want to know what kind of pickups Vince Gill uses in his Tele, because if I had those, as good of a player as I am, I'm sure I could make it sound like that.
Only badly."

Don, not sure how many pinholes you're getting, but this is from the Collings website:

" Unlike lacquer, the process for applying varnish is not conducive to "finish touch-ups", meaning that we cannot repair some minor imperfections such as small pinholes, bubbles, or sinks. While we've always taken pride in our high standard for fit and finish, we cannot produce varnish instruments to the level of cosmetic "perfection" as we can with our lacquer finish instruments. "

They seem to accept some pinholes.