Ok, I'm a moron. Hard as I try I just can't seem to get the hang of this clear coat. I have little trouble with the primmer or color coat but just seem to either over-power (run/sag) or under power, pebble the finish with the clear coat. I posted on this before and got a couple suggestions that helped a little but I'm still having trouble. I did a search on the topic which turned up a lot of bits and pieces of the process but I didn't find a comprehensive guide. My local supply guy says that he thinks I'm recoating to quickly and that the temp in my garage could be contributing to my problem. It has been well into the upper 90s and over a 100 with high humidity here for weeks.

So, could you professionals give us a step by step on the application of CC. For example, tip size, air pressures, time between coats, how many coats, temp and humidity pit falls we need to watch for, tips/tricks etc. And also a step by step on color sanding and buffing which I know has been covered before, but maybe a "Martin's how to" type lecture covering the entire process start to finish.

On a side note. If we can keep getting martin and the guys to write enough of these great articles for us we can just combine them, shoot some pics and put a book together.

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72 Chevelle and a 70 Chevelle with a crushed roof
ACES # 4051 MCC # 448
TC # 1549 81/70 Cruisers

[This message has been edited by Professor_SS (edited 08-20-2002).]

Prof.. You should be following your tech sheet. However I would wait on the outside of your CC re-coat window (so if your max is one hour wait 55 minutes) Shooting with a 1.3 1.5 tip should be fine and keep your pressure at 50psi or so (depends on which gun you are using) pay close attention to your spray speed and overlap, I bet that is where you are doing all of the over/under shooting, Overlap 50% minimum and work a bit faster than you did with color. I noticed when I was having trouble with clear that I was slowing down because I couldn't "See" coverage. Some more info could help us help you..

Gun
Cap Size
PSI
CC brand and part number
overlap
Fan settings
and material setting

This should help us get a hand on your issue.


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X-Ray View of my Chevelle :D (http://www.normieschevelle.com/sideview.jpg)
Getting Closer (http://www.normieschevelle.com/passfull.jpg)
my baby in primer (http://www.normieschevelle.com/prime/primerdrv.jpg)

Watch your gun technique. Make sure you are holding you gun with the air cap exactly perpendicular to the body surface. If you hold it on an angle, You could be getting too much paint on some areas and not enough on other. If you are doing this correctly, the rest is influenced by many factors, such as, gun type and set-up, gun distance, gun speed, Brand of clear, hardener speed, reducer speed, weather conditions, booth air flow. All of these factors make it next to impossible for anything but a professional painter to get a show quality finish.

Gordon VM
Restoration Motorsports

Ok, some quick info,

gun = DeVilbiss 615 cup GFC-502
tip = 1.6 for primmer and 1.4 for color and clear. I use the plastic liners with the gun.

Garage = falling down old two car with lots of dirt and pi$%# poor lighting, but the best I can do. I have purchased a canvas canopy with sides that I have visions of pressing into serivce as a semi clean environment if I can work out venting.

air pressures = 40 at tank 60 gal single stage compressor dryer at tank 25 feet of hose, another 15 feet of hose with an in line filter/dryer at the gun, gun gage set at 15 lbs.

PPG paint and clear with recommended hardners and thinners = color is Deltron 2000 and clear is DCU 2021.

Temps = again it has been very hot and humid here. I would say I've been working in upper 90s and 50-60% humidity for last three weeks. kind of hard keeping even 90% angle on things like head light extensions (off car, lying on bench) and the underside of the hood (off the car and up-side down on saw horses) and the valance (hanging from hooks), which is the only parts I've attmepted other than the cowl at this point.

the cowl came out ok as did the inside/underside of the fenders, a few sags/runs but most in places where they cannot be seen. I just don't seem to be improving so thought there might be some pointers I'm missing.

One just mentioned, waiting up to an hour between coats. My PPG supply guy said 15 mins or so. which is what I've been doing, does temp affect this wait period?

BTW this is the 72 the entire cars was stripped and is in primmer K36 PPG and the color is bright orange if that matters.

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72 Chevelle and a 70 Chevelle with a crushed roof
ACES # 4051 MCC # 448
TC # 1549 81/70 Cruisers

Is your gun pressure really have only 15 lbs?
if so, that's one thing that needs corrected. Big time! You should be using 40-60 @ the gun with a regular siphon or gravity feed gun.
Atomization is critical.

Mu PPG sales guy told me to run 40 at the tank 15 to 20 at the gun. Where are you running 50 PSI?

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72 Chevelle and a 70 Chevelle with a crushed roof
ACES # 4051 MCC # 448
TC # 1549 81/70 Cruisers

I run a small gauge/regulator right before the in-line filter at the gun. 35-45 at the gun for my set-up. 15psi at the gun is too low.
On another note, try to improve your lighting, it'll make a way-big difference, or at least in your attitude while spraying http://www.chevelles.com/forum/biggrin.gif

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'68 SS-396 (still workin' on it)
"Need a good hobby?? I recommend drinking"
-2 Below Custom Automotive
Fbks, AK.

I checked the lit that came with the gun and talked to the sales person that sold me the gun and both say, 10 to 15 pounds at the gage at the gun for BC/CC and 15 to 20 for heavy solid primmers. The sales guy says you guys must be running a different type of gun and if I run that kind of pressure I'll create a "cloud" of overspray and more runs than I have now. I'm confused. My gun is a HVLP gun with a top cup. I'll give it a increase in pressure a try and see what happens and I'll let you know.

Also, I know what you mean on the lighting thing. I'm working on that, I'm putting together a couple of portable spot lights thta I can move around so I can see better. These darn bi-focals don't help matters much either.

Thanks guys, keep them suggestions coming.

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72 Chevelle and a 70 Chevelle with a crushed roof
ACES # 4051 MCC # 448
TC # 1549 81/70 Cruisers

[This message has been edited by Professor_SS (edited 08-22-2002).]

My gravity feed hvlp sprays clear at 50-55psi at the gun. I normally use Diamont dc-92, and Limco lc-4000. Another identical gun is used for primer, color coat apps. I find they spray the best at 28psi, this depends on reduction as some primer surfacers are quite a bit thicker.But for 2:1 cut base, 28 works best.
I had airflow problems, runs,sags, severe orangepeel, even solvent pop. before i "figured" out how to lay this damn clearcoat stuff, by then ive wasted alot of good paint. I think correcting the shop airflow problems and lighting the place up made the biggest difference.
A friend who happens to be a sheet metal worker, cut a hole in the roof and installed a vent, ducted a blower fan on the wall, and 2 intake vents (all filtered). I also installed a cheapo used 220volt a/c unit at the back of the shop which is 14x32. Big difference, almost zero overspray, much cooler in there(dripping sweat on fresh paint is a big minus).

I'm no pro, but I came up with an idea for lighting that worked great. Clear Christmas lights, they give you lots of tiny reflections, I could see much better.

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64 ElCamino (http://mediaservice.photoisland.com/auction/Jul/20027306594843713937468.jpg) 350 700r4 3.42 posi

Prof listen to the tech and the manual.. It sounds like you have a low volume gun.. Just follow directions.. Sounds like you are just shooting heavy.. Try turning the meterial knob back a turn.. and spray as normal. Be mindful where you are spraying and remember runs and sags can be sanded out in clear.. I wouldn't worry if they aren't too bad... Sounds like you have it under control http://www.chevelles.com/forum/biggrin.gif

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X-Ray View of my Chevelle :D (http://www.normieschevelle.com/sideview.jpg)
Getting Closer (http://www.normieschevelle.com/passfull.jpg)
my baby in primer (http://www.normieschevelle.com/prime/primerdrv.jpg)

I am NOT an expert on eqipment by any means. But, I understand HVLP guns to work with low pressure and a greater QUANTITY of air. A 1/2" hose is usually recommended. If you're using a true HVLP gun with a smaller 3/8" hose, that may be a problem. Even the HVLP gun that I have (Not true HVLP) uses 45-50 psi @ the gun for Clear coat. If I used 15 psi, it would be VERY hard to lay down a good coat of clear. Just try 45 @ the gun and see what happens.

thanks guys, I ran the pressure up to 40 PSI at the gun inlet today. I'd had a better pattern if I'd thrown a can of paint at the parts from accross the room. the worst sags, runs yet. I did rig up a good lighting source and got a box fan going to move some air but the higher pressure is not the answer. The lit that came with my gun suggests a "max" pressure of 28 lbs at the gun inlet which they say results in 10 at the nozzle. Maybe that is what they mean by 10-12 at the gun. My sales guy still insists that 10 to 15 at the gage on the gun is correct So, Tomorrow, after it is dry (again) I'll sand it again, and if it needs it I'll try to coat these two parts again at 28 PSI. thanks for all your input.

I'm becoming convinced that I'm going to have to find someone to paint the car for me. I just don't think I'm getting a handle on this. Problem is, I've arranged two different guys to do the work and both back out or left me hanging!!!!

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72 Chevelle and a 70 Chevelle with a crushed roof
ACES # 4051 MCC # 448
TC # 1549 81/70 Cruisers

Professor, I have a devillbiss finish line 2 hvlp gravity feed gun , The directions say that you should have 25psi at the gage on the gun with the trigger pulled, I run 75 psi off the compressor up to the gun gage, then I pull the trigger and adjust the pressure to 25psi and that gives me 10-12 psi at the cap. double check your directions to see if your gun needs the same procedure. Good luck.

Hold the boat here. The 10 lbs at are at the CAP. You have no way of measureing this. They only put it because it is the "LEGAL" maximum. An HVLP gun can have no more than 10 Lbs and 68% transfer efficiency to be legal (at least here in Ca.).

The only way to measure it is with a cap that has a guage on it. These caps cost in the $150.00 range. Set the gun at the manufactures recommendation and you will have close to the 10 pounds at the cap. This recommendation is stamped on the gun, again, it is LEGAL requirment to have this on the gun.

Here is my "Basics of Basics" on gun set up for you. Hope it helps out.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> Painting basics
Being HVLP and low VOC products are the way the industry’s going I will be referring to them in this discussion on painting and paint guns. Most all basic issues dealing with HVLP can be applied to conventional guns, atomization is atomization. The HVLP just arrives at it differently.

The object of the spray gun is to break up the primer/sealer/paint/clear (I will call this “PSPC” from here out) into small particles and lay them in neat little rows on the panel being PSPRed. So the whole outcome rests on how well the gun is doing this. Picture the droplets of PSPC coming out of the fluid tip of the gun and then the air “slapping” them into smaller droplets.

You have two things that help you with this process, air and solvent. Solvent can mean something that is already in the PSPR from the manufacture or something the manufacture has told you to add to it. By the way, you should always mix in proper ratios as instructed in the tech sheet. The thinner (less viscosity) you get the PSPR or the more air you have at the fluid tip of the gun the more it will break up the PSPR. The target for you is getting the perfect balance needed. Too much solvent and the PSPR will have no body, fill, durability, etc. Too much air and you blow the PSPR everywhere but the car, poor adhesion, excessive texture, etc.

So, the answer is proper air supply and gun (and fluid tip) choice and how you adjust it.

With today’s high solids-low VOC (Volatile Organic Compound, you know the bad stuff that goes up into the air we breathe) products there is less solvent. And with HVLP guns there is less air at the cap to break up the PSPC, proper air supply and gun setup is more important than ever.

FIRST THINGS FIRST, your compressor and air supply.

An HVLP gun requires more VOLUME of air to operate (the V in HVLP, High Volume Low Pressure). Now you may notice that your HVLP gun is adjusted at maybe the same PSI as an old conventional gun, around 50 lbs at the gun (many HVLP guns are set at much lower though) so where is the “Low” in PSI they are talking about? It is at the actual air cap where the air and paint come out. An HVLP gun has only 10 lbs at the cap while a conventional has upwards of 50! So the VOLUME of air (CFM, Cubic Feet per Minute) is the key to proper atomization with an HVLP.

If you have a gun that requires 15 CFM you will need a compressor and plumbing that will produce that at a very minimum. There are HVLP guns that need as little as 7.5 CFM so you can get good results even from a smaller compressor. Air supply is a complete subject by it’s self so lets assume that you have the air supply needed and move on to gun set up.

So atomization is the key, but why? Why can’t you just lay it out wet and let it “flow”, as an old painter will say. Picture a jar full of bb’s, they will represent well small, atomized droplets of PSPC. The gaps in between the bb’s is solvent. Now picture a jar filled with marbles, they will represent large, poorly atomized droplets of PSPC. The gaps in between are, you guessed it, solvent.

If you apply your PSPC in large poorly atomized droplets, what you will have is a film full of solvent. This can and will cause slow curing, shrinkage and dieback (the loss of gloss in the hours and days after application).

So, now that we have learned the need for gun set up, how do we do it? Lets start with the fluid tip choice. The newer high solids low VOC PSPC products need to be broken up more, so a smaller fluid tip is needed.
Basically you want the smallest fluid tip that will still allow you to PSPC the particular part you are PSPCing keeping the entire thing wet and in a fair amount of time. In other words a 1.0 tip would be beautiful for clearing one fender, but would be lousy to paint a complete. The application would be way to slow and the first panel would be way to flashed by the time you got around back to it. So you need to compromise, a 1.3 is a great all around tip, while a 1.5 though getting a little big, can get you by. If you read the tech sheet on the particular product you are shooting, it will have a recommendation for fluid tip size.
There are needs for other tips, for instance when shooting polyester primer you may need as big as a 2.3, but for urethanes and epoxies, the 1.3 or 1.4 will work great. If you plan on using a pressure pot or paint a bus, all bets are off and we would need to study a little bit more.

As an example of the use of a 1.3 tip I did a test once that proved the point well. I shot two panels of metal with a med solids urethane primer. One was shot with a 1.3 super high atomizing top of the line topcoat gun. The other was shot with a 1.5 (or a 1.7 I can’t remember) “hoser” primer gun. Three coats were applied and after a full cure (the one shot with the larger gun took MUCH longer to flash and cure by the way) the film thickness was measured. The one shot with the 1.3 tip was 2 tenths of a MIL thicker! The larger gun laid out the marble sized droplets full of solvent and when the solvent flashed the film shrank.

Air supply is a subject that could fill many pages by it’s self. So we are going to assume you have that covered and move on to gun set up.

You need to “tune” your gun EVERY TIME you use it just as you would tune a guitar before you perform. This is done with a very basic spray out pattern test. This very basic test tells you how your gun is atomizing and you adjust it to achieve the best atomization you can.

Lets do a spray pattern test:

Set the fan width as need (you don’t want to change it after you have “tuned” the gun). Turn out the material knob about 2 ½ turns. This is the “mixture” adjustment, kind of like the idle screw on a carburetor. The farther in it is screwed the lower the fluid to air ratio is and the smaller the droplets will be. The farther out it is, the higher the fluid to air ratio is and the larger the droplets.
Set the air pressure at the inlet to the gun to the manufactures specs. On an HVLP gun this spec is usually found on the gun and is the maximum PSI it can have while still maintaining the maximum 10 lb at the cap for legal HVLP transfer efficiency (68 %). You are now ready to do a test spray out.

Tape a piece of masking paper on the wall for the test. Hold the gun at a right angle to the wall, just as if you were going the wall. Hold the gun at a spread out hands distance (about 8” or 22cm). Pull the trigger to completely open for a split second and then close it. You want an ON-OFF wide open-completely closed in ONE movement. You should have a cigar shaped pattern with complete coverage in the center with fading coverage going away from the full coverage cigar shape in the center. The center should be fully covered without any runs. If you have runs, either you are holding the trigger too long, you are too close or the gun is simply applying too much material. In which case you need to screw in the material knob or turn the air pressure down. But most likely if you have turned the material knob out the 2 ½ turns and the air is set at the factory specs, you are just too close or holding the trigger open too long.

The droplets you see trailing off the center are what you will use to “tune” your gun.

Turn in the material knob to make the droplets smaller (and or raise the air pressure). The balance you need to attain is the smallest droplet size possible before you loose the coverage desired. In other words if you turn in the material knob too far, not enough material will be coming out to cover the panel!

Now, you’ll notice that I said, “raise the pressure to the gun”, while earlier I said to set it to manufactures specs. We are talking a very small adjustment. It is a fine balance in material to air ratio and a little more air than specified is okay. Even if it is an HVLP gun the inlet pressure recommended is to maintain the 10 lb limit at the cap. Well, about three quarters of the country has no regulations for HVLP use so if you go over the 10 lbs all it will do is atomize the material a little better. You may loose a little of the benefits of HVLP though. But remember you have a lot of control with the material adjustment knob.

After you are happy with the droplet size, DON’T TOUCH THE FAN CONTROL. It will change the PSI at the cap and will change the atomization you worked hard to get.
Do this spray out every time you spray as material change, temp, and humidity will necessitate a spray out droplet pattern test. Good luck!

Check out this URL to see an example of a sprayout pattern. http://members.aol.com/icantunderstand/hvlpdropletpatterns.jpg




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1965 Buick Gran Sport Convertible
1965 Buick Skylark H/T
"Fan of most anything that moves human beings"