Any idea what Im doing wrong spraying GF high Perf

[bruce buren]

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Here are a couple sample boards I did with oak plywood sanded to 150. I am getting little bumps in the finish. I am using a Wagner conversion gun from gleem paint 1.3 tip no thinning of GF high performance

thanks in advance for any help/suggestions
Bruce

[Jamie Buxton]

My experience is that the first coat of any waterborne "raises the grain". I think the water raises any little wood fibers that aren't completely tacked down, and then the finish freezes the fibers in that stuck up position. Light sanding with very fine paper flattens those nibs, and you can get on with subsequent coats. When I say very fine sandpaper I mean 320 or even finer. When I say light sanding, it is really just a few swipes by hand. You'll immediately feel the difference in surface roughness.

[John TenEyck]

If your gun is a gravity feed HVLP gun you need at least a 1.8 mm N/N to spray GF's HP, and you will likely still have to add about 5 - 6% H2O to get the viscosity down to around 50 seconds #4 Ford cup. With a 1.3 mm N/N I think you will need to add at least 10% H2O, and I'd rather not do that. But if you decide to go that route, you will need to get the viscosity down to 20 - 25 seconds for it to spray well.

Once you have the viscosity matched to your gun you want to spray a 3 - 5 mil coat. Your photos suggest your wet coat is too thin and is drying before it flows out. If true, you should spray a heavier coat (but not so heavy that it looks blue). Adding Extender often helps, too, in giving the finish more time to flow out before it sets. I typically add about 3% to most clearcoats.

I hope that helps.

John

[bruce buren]

thanks for the responses guys.

John the gun is a cup style. I will try a heavier coat

[Ed Edwards]

This Question is for John TenEyck ,
John,
I have followed your advise for a long time now. What is the N/N in "1.8 mm N/N"? Pardon my ignorance.
And #2, what extender do you recommend?

Not trying to hijack the thread, just trying to learn
Thanks, Ed

[John TenEyck]

This Question is for John TenEyck ,
John,
I have followed your advise for a long time now. What is the N/N in "1.8 mm N/N"? Pardon my ignorance.
And #2, what extender do you recommend?

Not trying to hijack the thread, just trying to learn
Thanks, Ed

Sorry not to clarify, Ed. N/N = Needle/Nozzle size. So, 1.8 mm N/N means a needle of that size and the corresponding nozzle that goes with it, which might be different from one brand of gun to another.

For clear coats I use General Finishes' Extender, generally at 3% based on volume. For waterborne paints and pigmented lacquers I use Benjamin Moore's Extender at 3 - 4%. GF's Extnder is clear and could be used in any WB product. BM's Extender is milky white so I woudn't use it in a clearcoat product. I've never done a direct comparison test, so I can't say which is more effective when added to paint.

I hope that helps.

John

[Ed Edwards]

Thanks John,
I appreciate your response. I always learn something new when visiting this site!
Ed

[Jebediah Eckert]

Thanks John,
I appreciate your response. I always learn something new when visiting this site!
Ed

+1 for sure!