Painting Experts - Single Stage Metallic [Archive] - Chevy Nova Forum

: Painting Experts - Single Stage Metallic


jeffa55
20th-April-2009, 11:09 AM
I'm hoping a few experienced painters can answer some questions that I have. First off, let me tell you that I am using an OMNI single stage metallic paint with a Devlbliss Starting Line HVLP gun. I have the gun set-up with the supplied (it came with the gun set) air regulator at the inlet of the gun. I have the inlet pressure tuned to about 31-33psi with the trigger pulled. Here are my questions/problems (all of these paint experiences have been done over the OMNI urethane primer recommended by my shop):

1 - I painted the trunk lid by going left to right on the first coat, front to back on the second coat and then left to right on the third. I am left with tiger striping going left to right. What causes this? Is it gun set up?

2 - When I am painting, the first coat seems to go on quite glossy with an acceptable level of orange peel. The second coat goes on with more peel and the third with even more. It ends up so that you can't make out your face when you look at it from only 2 feet away. It still looks glossy, but very 'hazy'.

I 'believe' I have the gun set-up right, but I am not sure. I have the 'air inlet' contol at teh bottom of the gun set to 'all the way open'. I assume I should do that since I am controlling the air with the external regulator at the inlet?? I have the spray pattern at about the 6-8" long thing so that looks good. I am not 100% sure how to tune the material volume. I can open it utnil it runs, but should my procedure be to get it to that point and then tighten (lower the material) until is stops running tha that is where you leave it? I just don't seem to have the tuning down right.

The paint is saying to wait 5-10 minutes as the flash time and I have two questions about that. 1 - what typically happens if you don't wait long enough? 2 - what happens if you wait too long?
Between coats is it OK to just leave the paint in the gun and then spray the second coat and then the third? It seemed that the paint might be hardening in the gun and maybe that was causing my problem from #2 above (the fact that the 2nd and 3rd coat were signigicantly more peeled).

I am sure you will need to ask me questions in order to give answers, but shoot away. I really am enjoying this paint thing!!

TechNova
20th-April-2009, 12:28 PM
1. changing directions on the trunk lid is doing you no good, it just puts the streaks in another direction. The streaks can be caused by gun setup or spray technique. Some paints are going to streak no matter what.
The fix is to turn up the air pressure, increase gun to panel distance and "fog" in a coat at the end. I have always done this in an "X" pattern across the panel. Paint in your normal front to back for the full wet coats and fog in a coat diagonally each way.
You must do this to each panel immediately after spraying the last full wet coat to the panel. If you wait it will go on dry, you need it wet so the fog melts in.
You need to have proper (or at least close to proper) gun setup and technique for this to work. oval shaped spray pattern, 50% overlap and consistant passes are the key.

2. Harder to answer. Is your vent on the gun cup obstructed? Your second and third coats should be wetter than the first, are you spraying them that way? The paint should not be getting hard or changing between coats.
Your tech sheet will give a pot life, don't exceed it. You can have solvent pop issues if you recoat too soon. You can have lifting issues if you wait too long. You didn't post the type of paint, but acrylic enamels are very forgiving on recoat times, others are very sensitive. I usually have my material adjustment way out then adjust my painting travel speed accordingly.
What size tip is in the gun??
Have you tried increasing the air pressure to get better atomozation?

jeffa55
20th-April-2009, 12:47 PM
THanks for the info!

1 - The gun's cup 'hole' is not obstructed
2 - I am using Acrylic Enamel
3 - The gun's tip size is 1.3mm

I will try your suggestions. When you say that the second and 3rd coat should go on 'wetter' do you mean that I should increase teh material flow with those coats? I am thinking that I don't have enough material flowing and that I need to increase that. It sounds like I should start 'heavy' and then back it off? When I am spraying a test panel, what is the sign that I am at teh right setting - should I get it to the point that it is just inside of sagging?

Thanks again

TechNova
20th-April-2009, 03:18 PM
I do not change the gun material knob once it is set. Adjust your travel speed
to make the coat wetter or drier as needed.
I have sprayed very little AE on cars recently (I use it alot on equipment) but I think the 1.3 tip is small. I have sprayed hundreds of gallons with the old style guns but do not know how the tip sizes compare.
Someone else may have tip size input for the new guns with metric size tips.

slownova73
20th-April-2009, 04:23 PM
you should hold the gun at a distance of 6 to 8 inches from the surface u r painting, do not swithc directions with metallic colors, or any for that matter, and orange peel comes from the painter, a very experienced painter has les orange peel than less experienced painter, it goes away with time, the better your technique the less orange peel, never let all the way off the trigger, the gun is a 2 stage trigger, the first is air only spraying then squeeze a little more and it sprays, never completley let go of the trigger, when you let off let off on the spray stage only keep the air going, and always yuse a 50% overlap technique, spray across then cover half of your previous cross with the next one. hope this helps

jeffa55
20th-April-2009, 05:36 PM
OK - I got the 'don't change the material flow once it is set' and I'll do my variation with the speed of my pass. How do I get it set to begin with? Any tricks?

Dork
20th-April-2009, 07:10 PM
I typically run the material knob turned almost all the way out. You can set it wherever you like. More open and you will have to move faster, more in and you will have to slow the gun down. Single stages metallics can be a pain even for an experienced painter. Are you using the correct temp reducer?

tnblkc230wz
20th-April-2009, 07:25 PM
I'm no expert, but I had a similar problem with my painting. I got lots of help from Technova, Customproducts and many others. My tiger striping was all technic. Once my gun was set, It didn't touch it.

I sprayed my final coat moving the gun 2.5 times as fast as the first two coats. I made sure my tip was parallel to the surface. I made sure my paint cup was only 1/3 full so it wouldn't clog/leak from the vent hole while painting the roof, hood and trunk. I also overlap each coat at least 50%.

I stilled had a little bit of striping showing through, so I sprayed a fourth coat and it looks good now. Now I just need to sand the runs out of the clear :eek::eek::eek:

TechNova
20th-April-2009, 10:24 PM
OK - I got the 'don't change the material flow once it is set' and I'll do my variation with the speed of my pass. How do I get it set to begin with? Any tricks?

Somewhere I have some pics and text that say how to set the material and spray a test pattern. I'll see if I can find it.
I demo it by showing it with a loaded gun, I don't know how to put it in words.
You can hand me a gun putting out alot of material and I adjust on the fly by moving faster, you really have to read the paint as it hits the panel.

I really don't change my speed between coats, maybe a little slower on the last full coat. I have seen people speed up as tnblkc230wz posted with good results, it's just not my technique.

kenseth17
20th-April-2009, 10:49 PM
Pretty ambitious. For one your using a cheaper line, that may skimp on the pigment (think how candys are difficult being transparent) and poor metallic control to begin with, and your using it to shoot a metallic in single stage which can also be difficult. You will have to live with how it is shot, since you will not be able to buff, unless you clearcoat. You need to maintain both a good gloss and even metallic.
Single stage metallics can be a bit tricky even for someone with a bit of gun experience. I shot some single stage metallics when I was starting out in the late 80's, and even though they turned out fine, would not want to go back now that basecoat has taken over, even with more experience painting and having better guns.
But what we did when shooting them is went back and did a mist coat. Basically jump back and forth between panels. Make sure you have good gun setup, spray a good wet enough coat, keeping the gun parallel and proper overlap. If you don't have these you will get striping. But if you still get some striping or mottleing, even it out with a mist coat described above, by upping the pressure a tad, backing up the gun distance and spraying at different angles over the panel. Spray one panel, move to the next, go back and mist coat the previous panel by spraying at different angles over the panel to help even it out. In this time hopefully the previous panel has set up enough that when spraying you mist coat it will not contribute to more mottling, but still be wet enough to accept it and maintain a good gloss. And although this goes against the whole pigment transparency thing, maybe over reducing a tad will help with getting the metallic to lay out better, and a slow reducer to keep things open longer and more time to accept a mist coat. Can't remember if omni ss gets reduced or not, but you could if you wanted using a good grade of urethane reducer. You don't want to be using a fast reducer. And although I am not familiar with the devilbiss starting line, and it says hvlp, I think you should give upping your pressure some a try.

jeffa55
21st-April-2009, 08:27 AM
Thanks for all of the info everyone. I'm going to wet-sand the trunk (to get it really smooth) and then re-spray it this weekend trying these tips. We'll see how it comes out. I'm going to play around with the trunk for a while until I get the technique right and then I'll shoot the car.

The EnforceR
23rd-April-2009, 11:36 AM
This is my personal car and was done using OMNI single stage metallic paint. i used the same settings you have mentioned. my main concern was to not allow the metallic to get splotchy (aka darker in some spots that others). just keep the going at the same pace, and same distance while painting. i had to change directions in some spots here of course, but with a trunk lid keep it consistent as others have said. btw, i am no expert, and i am hardly an amatuer. just some stuff i learned the hard way that wou might can learn.

http://i21.photobucket.com/albums/b288/kyles2000z/Z28%2009/084.jpg