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Discussion Starter · #1 ·
I'm spraying a test piece using waterborne lacquer. The first and second coats leveled beautifully, but the third and subsequent costs have what appear to be zillions of tiny bubbles in it. I've experienced something similar with nitrocellulose lacquer which I believe was solvent pop, but waterborne shouldn't get solvent pop, right? Initially, the wet coat appears to look perfect, but then these tiny bubbles seem to appear as it's drying. On my last test coat, I immediately covered the piece with a box top to make sure it wasn't just airborne dust and I still have what appear to be tiny bubbles. Any idea what I'm doing wrong?
 

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The first and second coat probably absorbed into the wood so it didn't really build a coating. With the third the wood was sealed enough it dried on the surface. The bubbles were caused by the finish not being thinned enough. While it may have worked great for the first two coats start thinning the finish for the later coats. Also if it is hot where you are that plays into it as well. The finish gets air in it while it is being sprayed and if the finish dries before the air can get out of it the bubbles form. Thinning the finish will slow the drying time. It's possible in cooler weather you may not need to thin the finish.
 

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I'm spraying a test piece using waterborne lacquer. The first and second coats leveled beautifully, but the third and subsequent costs have what appear to be zillions of tiny bubbles in it. I've experienced something similar with nitrocellulose lacquer which I believe was solvent pop, but waterborne shouldn't get solvent pop, right? Initially, the wet coat appears to look perfect, but then these tiny bubbles seem to appear as it's drying. On my last test coat, I immediately covered the piece with a box top to make sure it wasn't just airborne dust and I still have what appear to be tiny bubbles. Any idea what I'm doing wrong?
Need some more info in order to figure out what you have. A picture would help.

What wood are you using?

What was it sanded to before the first application of anything?

Is there a stain applied, and if so what exactly is it?

Was the first application sanded before applying the second?

What waterbase are you using?

What gun are you using?

What size compressor?

What pressures?

Was the gun used for any other finishes? If so, what were they?

What was the ambient temperature, and relative humidity?

What filters do you use?

Are there moisture taps along the airline to the gun?

When was the tank last drained?






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Discussion Starter · #4 ·
I'm testing on maple since that's what my finish will ultimately be on. I dyed with TransTint dye which dried for a week. I sanded to 400 and sand between the first two coats with 400 and between subsequent coats with 600.

I'm using a DevilBiss gravity feed conversion gun at 15 psi with a 1.2 tip. The finish viscosity is 12 seconds in a Ford cup. The finish is Grafted Coatings KTM10; a waterborne lacquer.

I have a separator at the compressor and an inline filter at the gun.

Sorry, no picture right now, I sanded everything down to try another coat.

Tonight I tried a couple of things that resulted in some improvement.
I use the DevilBiss DeKups system which allows for a little filter in the fluid path between the gravity cup and the gun. Most folks recommend against this but I thought I'd give it a try, so I put one n the gun. I also warmed the finish in hot water. These things seemed to help quite a bit. If only I knew which one! Any guesses which one it was?
 

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I'm testing on maple since that's what my finish will ultimately be on. I dyed with TransTint dye which dried for a week. I sanded to 400 and sand between the first two coats with 400 and between subsequent coats with 600.
You used Trans Tint dye...in what? Sanding to 400 is too smooth IMO. I would stop at 180x. In between coats I would use 320x.






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Discussion Starter · #6 ·
The Transtint was dissolved in Alcohol. I let it dry for a week, then sanded before applying the topcoat
 

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The Transtint was dissolved in Alcohol. I let it dry for a week, then sanded before applying the topcoat
I wouldn't sand the stain/dye application. I would apply sealer or topcoat in thin applications, and not sand until a few, in order to get some build. You don't want to sand through the first coat to get to the stain.




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I think the tiny little bubbles are sanding dust, 400 + sanding paper will creat a really fine powder, if you were just blowing sand dust with a compressed air it will not remove it, you need to wipe it of with a rag of tac rag or a micro fiber rag which i find it useful.
 

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Two really big areas of concern.

One pointed out above....dust,grit,whatever.Finish rms need to be seperate from machining rms.And I really don't want to hear about anyone's problems with this,haha.Figure it out....because if a person continues to "finish" in the same rm they're grinding in,you're not gonna get a lot of sympathy.Wall an area off with plastic...whatever it takes,just do it.

Next point is understanding what's going on inside your AC(air compressor) and your hoses,which ultimately ends up in the gun and finish.HVLP guns don't like those little bulb filters hung on the gun.They also don't like sm diameter hoses.Clean up your act,so to speak,WRT the funk in the AC and hoses.

As your theropist,stop blaming the finish...you have to look inward.Find the real cause of your pain,haha.The very best of luck.
 

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The Transtint was dissolved in Alcohol. I let it dry for a week, then sanded before applying the topcoat
If you mixed the Transtint with alcohol it would have been dry enough to topcoat within 5 minutes. The stain had nothing to do with the bubbles. Bubbles and blisters are nearly always caused by the finish being too thick. It can also be caused if the fresh finish was exposed to sunlight.
 

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Discussion Starter · #13 ·
Here's a picture of my rig

Here's a picture of my setup. Does anyone think the filter should be on the other side of the regulator?
 

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Here's a picture of my setup. Does anyone think the filter should be on the other side of the regulator?
Yes, I mount the regulator/gauge right on the gun, and the filter to that. You'll be changing the filter, and you don't have to remove the regulator/gauge. The filter will also prevent last minute moisture/debris/gunk from getting to the regulator/gauge.




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