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PhilC
09-01-2007 16:02:46
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Re: Having painting problem, need advice. in reply to chooch, 08-27-2007 15:51:50
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I'll just add a few comments to those you've already received. First, as the others said, the temp/humidity is a factor in your problems. You need to use a slower reducer for higher temps, or wait for temps to drop into the proper range for the reducer you're using.
Second, you mentioned you added inline "driers" (I assume you mean bulb filters) due to increased moisture in your air line but did not adjust for pressure loss. You need sufficient air volume at the gun mfr's recommended pressure to properly atomize the paint you're spraying. With 2 bulb filters inline, you experienced a pretty good restriction in air volume. IMO, the reduced air pressure combined with too fast a reducer for the temp is the source of your texture problem.
Your comments on how you prepped your new sheetmetal are a little worrisome. I'm not familiar with DuPont's Nason, but know a lot of folks use it. Most etch, or wash, primers are not intended to be sprayed and then left for long periods of time without topcoating with sealer or 2k surfacer. Additionally, in my experience, etch primers are never sanded because it defeats their purpose. Properly applied, an etch prime will rarely have more than .5 mil thickness in the dried film. If you sand it, you've lost it and scratched into the metal you were trying to protect.
A visit to DuPont's site confirmed this. I checked the Nason tech sheets for 491-17 and 491-30 etch primers, and neither should be sanded. Recommend dry film build for both is .3 - .5 mils.
Neither tech sheet specified a "must be topcoated in x time" statement but both indicated a 15 - 30 minute flash time prior to topcoating. The sooner I can coat it with a sealer or 2k surfacer, the better. If I'm etching a panel, then I'm also spraying a surfacer as soon as the recommended flash time has elapsed.
You say you adjusted air pressure so you have 20psi at the gun while spraying, is that the gun and/or paint mfr's recommended pressure? It seems way too low to me. Most HVLP guns require around 30 - 35psi at the gun to obtain 10psi at the cap. Of course, you should adjust your air pressure to whatever your spray gun and paint mfr's recommend. Just remember to measure your inlet pressure at the gun with the trigger pulled. That means an inline pressure gauge mounted to the gun after all lines and filters. It's not adequate to set your pressure at the wall regulator with the trigger pulled because it does not account for line loss in your air hose or any inline filters that may exist. Yes, it is important.
The one thing we have not discussed is air volume, which is far more important than air pressure, especially when using HVLP. Others may argue with this, but IMO, if you don't have a true 5hp or larger 2-stage compressor with a minimum 60gal tank, then you're going to run out of air volume. That means you're overworking a smaller compressor, and that introduces lots of moisture in your compressed air not to mention a constantly fluctuating air supply. No fun to paint with those conditions.
Lastly, heed all of what Rod (NH) said in his post, every item is critical to achieving the result you're looking for.
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Rod