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  #1  
Old 22-10-13, 09:24
Dale Jordan Dale Jordan is offline
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Default spray painting question

I'm spraying larger parts at the moment using protec kharki no3 Enamel . Gun pressure 35 psi paint thinned 25% . Painting in the shade out of the wind parts not hot , after a light coat as flashed off I gave it a nice wet coat with 50 % over lap on each pass so paint looks wet and glossy . but when it dries it has shiny and not so shinny parts looks like tiger stripes showing where each pass went, looks patchy . Any tips would be great or is this normal and I being to fussy .. Dale
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  #2  
Old 22-10-13, 12:30
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Tony Baker
 
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Hello Dale! No, that should not be considered as normal. I have several questions about your spray setup etc. Some of the questions may not seem relevant, but all will become clear.

Firstly, are you using a hardener with your paint? I use Protec Barrier paint, Camoflague Green, Lustreless. It is an enamel, just like you are using, but the addition of Protec 369 (I think thats the correct code) effectively changes the enamel to similar to the 2 Pack paints of much higher quality finish. Another VERY distinct advantage to using the hardener is that it has a much faster flash off time. I have painted parts at 1000hrs and picked them up by the painted part to take them inside by 1600hrs. Dont try that with unhardened enamel.

While I had been a spraypainter for many years.......many years ago now, I couldnt comment on your quoted PSI, becuase we always went by the 'vibe' of the gun. I still do that today. My books though, tell me a pressure similar to yours is roughly correct, or maybe even slightly low. I change pressures dramatically, depending on the areas being painted, and if course part size. Also, the manner of application of your coats seems about right too, so i'm thinking problem may lay with your gun setup.

You didnt mention whether you are using a suction or gravity feed gun. For the first 5 years of my trade I used only suction. Then we got trained in use of the polyurethanes/ 2-Packs, where a gravity gun was used. I have NEVER used a suction type since. Chalk & Cheese, at least in my opinion. Hopefully, your gun will have a pressure adjustment on the gun handle. If it doesnt, buy a regulator to fit to it where the air hose goes in. It makes it sooooooo much quicker and easier to make the adjustments you will find helpful as you spray different areas of smaller parts or edges of larger. My favorite gun is not an expensive Iwata or Devilbiss. I use a SuperCheap Auto one. It has never let me down, and I can honestly say a megabucks one wouldnt have done better work. Be sure to sure to use a HVLP gun. That stands for High Volume Low Pressure. On the off chance you are using an airless gun......STOP! They wont give a good finish at all....ever.

I'm making the assumption you are using the correct reducer for your specific. You dont strike me as a fellow who would take a risk with mismatched products. Also I assume the paint has been mixed almost immediately prior to use.

The problem you have described sounds like a simple case of fan pattern adjustment, possibly combined with a less than perfect spray pressure selection. Can I suggest you take the gun, add an amount of paint you can afford to do without, then experiment with fan adjustment. At each different fan adjustment, alter the pressure both down below current, then slightly above said pressure. If doing these adjustments doesnt eliminate the problem, check you fluid adjustment. In fact, check that FIRST! It may be a simple case of increasing paint flow volume, but I suspect incorrect fan pattern is also playing a part. Are you using a flattening base additive, or is this premixed at manufacture? Flattening base added at time of your use can compound the visual effect of imperfect paint layup, but thats not something you can actually avoid. Discovering exactly what is causing your dry spray patches will eliminate the issue.

If the above things dont get a result, let me know. I have an old book with some good information, and will photograph some pages for you. In fact I will start looking for my favorite book anyway, just in case.

As always with my spray lectures, please excuse me if you already knew some (or all) of the above information.
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Last edited by Private_collector; 22-10-13 at 12:37.
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  #3  
Old 22-10-13, 12:55
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Tony Baker
 
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Hopefully you can see the writing on the following photo. I am presently using the tablet computer, and it's camera is CRAP!
Click image for larger version

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Spray about 1/2 a second of paint directly at a scrap of something flat, doing so at 90 degrees. Examine the pattern and compare to the examples in the poor quality photo, above.

If you have a fax number or email address you want to send me in a PM, I will copy and send you any applicable pages from the book. Bare in mind the textbook is old, the wisdom is timeless!
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Ford CMP, 115" WB,1942 (Under Restoration...still)
Medium sized, half fake, artillery piece project. (The 1/4 Pounder)
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Old 22-10-13, 22:49
Dale Jordan Dale Jordan is offline
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Thanks for the info Tony . I'm using a suction touch up gun for the smaller parts and a larger STAR S770 suction gun for big bits . The protec paint is pretty glossy so i did add a bit more flatter base , using enamel thinners , no harder plus lots of stirring mixing between coats . one thing i need to look at is my hose length is very long about 8 -10 meters and looking at this you tube below maybe my fan is to wide I'm trying to get to much coverage might need to bring it in a bit . looks like from your book i need to make sure when i do that quick test spray i have the oval spray shape pattern . Dale






http://www.youtube.com/watch?v=U-acl0BNGWk
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Last edited by Dale Jordan; 23-10-13 at 02:45.
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