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Reply by CaptainKlutz

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Posted on Strange behavior in finish when HVLP spraying

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CaptainKlutz

5033 posts in 2785 days


#1 posted 12-09-2019 04:41 AM

1st glance, your problems read like your gun tip is too small, and you need practice.

Not seeing the paint on surface is also worrisome. Guessing you need to to add more side lighting to your paint booth. With proper light angles, even if you can’t see the clear coating, you can a least see the wet sheen as it deposits and trail it leaves behind.

BTW #IAMAKLUTZ, not a spraying expert, but will offer a couple things I have learned.

1) Industrial paint suppliers will almost always have recommendations for tip size, gun type, and even pressure. Paint gun mfg also have recommendations. Asking your local supplier is usually good too, as they will know how to adjust based on local weather conditions.

That said, primers have fillers in them to smooth out surfaces. They need a larger tip size than a clear finish. While you can push primer through a 1.5mm tip, a 1.8-2.2mm is much better. But if you attempt to push thin lacquer through same tip, you get orange peel. For thinner paints like a lacquer, 1.4-1.6mm is more typical. What size to use also depends on type of gun. Airless systems can use smaller tips, than the gravity fed HVLP suggest above.

2) Thicker, heavy body paints like alkyd enamels require much higher level of atomization than thinner auto body enamel, clear, or lacquer. Orange peel is primary defect when poor atomization or too much material per pass happens. Have seen horrible orange peel issues in AZ due low humidity, spraying outdoors. Both my industrial paint suppliers suggest using airless, or turbine HVLP gun for alkyd enamels or WB poly as solution to low humidity orange peel. They produce more volume than a compressor based gun, which usually means better atomization. Based on this advice, picked up a used pressure pot feed Binks HVLP, and I have needed less reducer to get same results as my gravity fed HVLP guns. Alkyd paint is still temperamental, but it’s better.

3) If you can’t get better atomization, you need to properly thin the finish material. While you can use many reducer solvents to thin paint, they have to picked based on temp/humidity conditions at time of use. I have an entire shelf of various solvents, and proprietary reducers I use depending on when and what is being painted. Being a bit of chemistry geek, even have a chart of solvent evaporation rates and boiling temp properties that I use to help me pick the right solvents, and/or understand why various reducers have a solvent blend that works in different conditions, while others fail.
https://producerschemical.com/media/PC%20Solvent%20Chart.pdf
In cool weather, I want fast solvents. In warm weather, want slow solvents. Even with my past learning, In hot weather with temp is over 90°F, It’s almost impossible to spray heavy body finishes without some orange peel. So I don’t even attempt spraying when conditions are not right.

Hope this helps a little. If you want get best advice, talk to people who make/sell your paint/finish materials. They have a vested interest in your success. :-)

-- If it wasn't for bad luck, I wouldn't have no luck at all, Doom, despair, agony on me… - Albert King - Born Under a Bad Sign released 1967


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