Looking for Help with Spray Gun Adjustments

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Looking for Help with Spray Gun Adjustments

Postby Paul_NJ » Fri Jun 25, 2004 11:09 pm

Could somebody help me out? I am a novice with painting and need to learn set-up technique. I am restoring a 51 Farmall Cub, and am having difficulty getting a good finish using a HVLP gun. (It is a Wagner 3 stage 6 psi pressure feed unit). Currently the problem is with the primer. I have been using an OMNI 2K primer/surfacer (MP182) and will eventually use OMNI urethane over it.

Today I primed the hood/tank unit. I've been stripping a part at a time. The problem I'm having is that while I'm getting good coverage, I'm getting a dry, almost sandy finish - rough and granular particularly on the sheet metal. Cast is much better, maybe because it is rougher to begin with. Could there be a temperature influence? - today was hot - other times I have gotten a much smoother finish without any changes, but don't know why.

The directions call for 5:1 ratio between paint and hardener. I haven't been using any thinner. Should I be? How would I know how much? And I'm not sure what adjustments I should try to fix this problem. More/less air?, more/less paint?While I can sand down the primer now, I sure need better knowledge how to make the necessary adjustments before I actually try the top coat.

Any help would really be appreciated! Thanks
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Postby Rudi » Sat Jun 26, 2004 6:20 am

Paul:

I am no expert on automotive finishes, but I have been spraying catalytic lacquers for almost 40 years. So, I will give it a shot.

Seems you have 3 problems.

1. Ambient temp is not so much problem as ambient humidity but temperature can play a part, although I do not think this is your problem. Humidity can be anywhere from 50% to 75% and by adjusting the air a good uniform coat can be achieved, provided the paint/reducer/hardner ratio is correct. I have even sprayed at almost 100% humidity but then you run into problems such as orange peel and fish eyes even though those preventative agents are used.

2. Reducer/thinner is critical. Viscosity of the material is a real key to the problem. My first attempt at using hi-build primer ended up with a result similar to yours. I mixed it according to the instructions - used the correct amount of thinner etc. and still ended up with a dry coat. My chum up the road is a painter, so I consulted him as to the problem. Real simple - not enough reducer/thinner. I ended up adding almost a full part more to the mix. Once done the viscosity of the paint was much thinner and sprayed an almost perfectly even coat.

This is the root of your problem. Thinner is required as the primer's viscosity is too high? Can never remember whether thinned is higher or lower, but I think it is lower. The mixed primer/thinner should drip off the end of your measuring stick at about 2 to 3 drops per second roughly. I never use any other measurement technique except flow.

Try adding thinner/reduce. I am sure it will solve your problem.

3. Adequate air. Too much or too little will cause problems. If the air pressure is too high, the material can actually dry as it is vapourizing. Be careful with your air flow. HVLP guns are not something I use at all, but I assume they work similarily to their higher pressure cousins. I don't think this is your problem either.

My money is on number 2

Oh this is a quick post as I have to go drive me daughter to work. Will edit later if needed
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Postby Brent » Sat Jun 26, 2004 8:25 pm

Paul,
First, what part of NJ are you from? I was born and raised in Martinsville which is about five miles north of Bound Brook. Then moved to California when I was 23. I painted my Cub with a HVLP gun with great results. Never painted anything in my life until then. I mixed the paint 8 parts paint-4 parts reducer and 1 part hardener. It came out great. The right air pressure is important. With that mix I set the gun at about 50psi and it worked well. Only problem was my Ford 2000 industrial now has a Rouge Red bucket. I painted it for the practice before I painted the Cub. Hope this helps.
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Postby Don McCombs » Sun Jun 27, 2004 10:07 am

Paul,

Let me direct you to a really great auto body/painting web site. It is called the Auto Body Store and is located in NJ, maybe not too far from you. The address is:

http://www.autobodystore.com/cgi-bin/config.pl?index

Happy reading,
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Postby Mike Schmudlach » Tue Jun 29, 2004 9:14 pm

DO NOT SPRAY PRIMER OUT OF THE SAME GUN AS YOUR FINISH PAINT!!!
Primer takes a bigger size outlet then your finish paint.
Primer will ruin your good gun especially if you are spray high build primer. I started painting the old way which worked great for years until I got pickier.
I would use IH primer and IH 2150 as per directions with a good gun ($50-$75).
HVLP guns are not really made to spray enamels, they are better at base coat/clear coat.
My HVLP gun has about 50 lbs of pressure to the gun and has about 15 to 20 lbs at the tip. I did buy a good midrange gun ($125)
I am not a great painter but the Scout I painted 2 weeks ago won First place for Scout 80s at the Midwest Show at Red Power.
When I want a Cub to look original I use IH Paint because I can get an eggshell finish like they had originaly.
Painting like anything else takes practice. With a little practice you can do a great job. With years of practice (every day) you can do show cars. :-)
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