Well i started to do my first painting job on my jeep project im doing as my senior project for school. Well it looks pretty good so far but i was wondering if anyone had any tips and suggestions on what im doing. It seemed when i sprayed on the paint, it sprayed on in tiny blobs, then it would slowly smooth out as it dried. If i added more paint, it would sometimes run but the thicker coat of paint, the smoother the finish. Here are some pics on this website of what i'm doing. http://www.geocities.com/jamesca5/jeep.html
Does anyone have any suggestions. Do i need more pressure in the gun or what i was using 8-10psi in a hvlp gun with dupont acrylic enamel. you can see on the last picture on that website the texture of some of the paint.

Thanks,
Jim

1987 CJ7
customized with
a 351w engine
1989 yj tub

 

JIM, way to go!!! Your doing a great job!! Your finish will depend on so many variables. Heres a break down on things that have an effect on your finish:

1) temperature
2) gun use: keep the following in mind: distance, angle, trigger, speed, and overlap think DATSO
4) air pressure

HVLP guns are sensitive to air pressure. You also need to pay attention to the couplings and air lines that supply air to the gun. You can't use standard couplings when using an HVLP gun. Also, you need to follow the tech sheets put out by the paint manufacturers. Note: If you are using PPG they have a fax service that will answer any questions you have. The answer comes in the form of a fax and usually it only takes a few minutes. However, any paint rep will help you here. You need to call them (or visit the web site) if you don't have the tech sheets and ask them the following q's:
1) air pressure setting at the gun 2) fluid tip number you should use. The fluid tip is the part of the gun that sits inside the air cap and 3) air cap number.
I too suffered from same problems you did and solved them by adjusting the above.
You mentioned the mix of the paint. I would recommend not adjusting the paint and adjust the equipment instead. Having said this there are some important tricks you can use. First one is to use a slow reducrd on the last coat to get better flow (note: you can go from medium reducer to slow but not the other way). You can even get a retarder if you find you are fighting the flow ie., the paint is flashing off too quickly and your paint is not blending into the previous panel. You need to be able to control the drying time of the paint. This is done by adjusting the hardeners and temperatures in the booth and how much paint you put on. I also went as far as adjusting the air flow in my booth. I slowed down the fan. The result was better flow, and a heathier environment. The air pressure inside the booth was pushing the paint outside where people with respirators were breathing the fumes. My health is better and the paint jobs! I hope this micro analyses helps you.

 

thanks a lot for the help, that is wonderful. i will see what i can find out from dupont. i have a hvlp tip and a conventional tip on my devilbiss paint gun. i will see what they recommend for tips. I love the results so far and this site has really helped me out with some of my other posts. i really appreciate the help!

I think also what i need to do is heat my air line because my air compressor is outside in a cold environment and i know that that could be causing some problems.

So far i have carefully used a kerosene heater that pulls in air at one side of the room and shoots it not directly at the body but to the side and then i have two fans on the other side of my homemade booth pulling out the fumes. I turn the heater off while painting near it and when im done turn it back on and it gets to around 85 degress in there when its around 30-40 outside.

I think im going to do some final coats in the good weather but i need the jeep to be done in a month so i need some paint on it now.

 

You would be better heating the metal to be painted and the room you are painting In, be it a garage, barn, or Paint booth.

Sorry I do not see what heating the air will do for you. Our current temp is 30 degree's. Tonite I sprayed a 99 camaro, black. Sikkens base and PG products clear. My Quincy 20 hp 300 gal compressor sits OUTSIDE. the only thing heated is the oil tank. My next thought is that, when air is compressed it gets cold... CID do you have air heaters in your lines? If so id like to see em.. maybe my paint work would be that much better then.

DuPont recomends spraying @around 45 PSI...but be careful when playing with pressure, it WILL change the color being sprayed, either lighter or darker.
My thought would be to check with DuPont on the size needle and cap recomended for the product being sprayed.

BTW jimbo Congrats on doing your own paintwork!

 

hey thanks a lot,

well i let the heater on for a good half hour at least before painting to get the metal good and warm. (air temp around 85 degrees F)

I didnt think of that about the air, i guess it does get colder when it compresses because the molecules compressing. I was just going to sit two electric heaters up in front of my air line just before my booth to heat up the hose real good which would also heat the inside air

I'm guessing that 45 psi is for use with a conventional tip, not the hvlp? sounds way too high for hvlp. Some people say its easier or better to use the conventional tips over the hvlp tips? is that true?

 

I prefer conventional guns. All of mine are SATAjet 90's/ with 1.3 and 1.2 needle's and caps. The only thing that i have that is HVLP is my primer gun, and it does take some getting used to.

I never spray my color anywhere close to 45 with conventional.. im usually around 20. HVLP primer gun stays around 25 or 30, but can go as low as 15.

CID...Krosati..what pressure do you spray at?

 

I forgot to post this...

FInd a peice of scrap metal..Use it as a test panel.. to see what techinique works for you and waht air pressure does and doesnt.

 

i sprayed my primer at 8-10 psi on my hvlp gun and i have a convention tip that came with the gun. I found an article on dupont's website that may tell me the pressures/tips recommended. I painted the enamel also around 8-10 psi with the hvlp tip which it said in a painting book i have.

I found myself testing the spray on the walls of my paint booth which seemed to be a very bad idea because the primer flaked off and got all over the place so i will have to flip the walls inside out ( they are only plastic) before i do any more work.

 

Well next time try some news paper or something similar.. doesnt have tobe metal i guess. Paint will stick to paper. the paint Flaking off the plastic is why you see cars masked off in paper around the area's to be painted. just a tid bit FYI.

 

thanks that would be a good idea, i'll be sure to mask up some newspaper even on the walls so i dont get any paint on the plastic. thanks for the tip

 

Some confusion here I need to clarify. First my last post said people outside the booth were wearnig mask, no they were not. The high air pressure in the booth was pumping fumes outside.

Im not sure Jim I understand the part of the post about the air compressor. You say its outside and something about a heater. My compressor is in a different part of the shop away from dust but inside a heated location that maintains the same ambient temperature as the bodyshop. I do have something called a dryer on the lines. I have found after spending $600 on a filter for the lines in the booth I was still getting moisture from the compressor. I wish it was only moisture. With the water comes oil and one fish eyed finish is enough. The dryer has worked along with draining the compressor tank every 2 days.

4stars: I here you about the HVLP guns. I have enjoyed the suction fed units too. My first upgrade was from a JGA to a Sata sunction fed (SF). The first gun I bought out of high school was a brand new shinny Devilbiss JGA. I polished that thing every day. The next day I crossed threaded the cap!! SF I feel allow you to have more interaction with the application process. I dont know if you understand what I mean, its hard to explain. It seems like it requires more work to apply the paint. I mean this in a good way. When you lay on the paint you know what its going to do based on the appearance of the orange peel. You know what happens based on the sound of the air pressure too. Playing with the air between 30-45 psi and you know what the result will be. But HVLP, it doesnt throw out the paint like a SF. The surface (orange peel) is weird. Then there is the air pressure. Shooting at such a low pressure just doesnt seem right. But you know if everything clicks it works. I had to get a rep in to review all my equipment. I spent $1200 CND on 2 new guns, the GTI Devilbiss Millenium Series. I wasnt getting results and he changed my hoses and couplings. Also the cap combo. I use a 1.3 for bases and a 1.4 for clear. I stay under 25 psi for air pressure. I also slow down more now with the HVLP and let the gun do the work. This was a big change. These guns are so good I dont have to worry about mottling. Mind you, I have yet to shoot a complete silver! The added benefit is health. The HVLP came into being due to the VOC legislation. This is good because it means less pollution being dumped into the atmoshere and less over spray floating around in the spray booth.