Auto Spray-Gun Tips (Automotive)

Spray-Gun Tips for Automotive Painting

You don't need a new spray gun (even though you may want one) to get the most from your gun and to create a great paint job.

Every painter wants to turn out the best paint job possible. So what’s the key to a successful paint job?

A new spray gun, of course.

As a red-blooded American male, I just couldn’t resist. You can never have enough tools. Right guys?

Actually, a skillful painter with the correct spray gun (notice I said “correct,” not “new) is the right recipe for an outstanding paint job. But a spray gun is just like any other tool: It has to be matched to the job you’re doing.

(It’s also worth mentioning, even though it’s not part of this particular article, that a great paint job is almost impossible without proper surface preparation. See that article in the September issue of BSB.)

How Many Guns Do I Need?

Whether the gun is several years old or brand new, you have to take into consideration what material you’re spraying before you choose your gun.

Since the advent of VOC laws, the material you spray has changed too, so it’s even more critical to choose the spray gun based on what you’ll spray with it. For example, there are spray guns designed especially to spray clearcoats. Others are designed for primers and other heavy-bodied materials. Many painters also have a spray gun for primers and surfacers, another for basecoats and still another for clearcoats.

Having trouble with tricky mattes and metallics? Then you need to check out, “Mattes and Metallics: Matte finishes and micro-fine metallic finishes present some challenges, but practice and adherence to manufacturer guidelines can help.”

If you can afford to have three spray guns, this is the ideal scenario. At the very least, you should consider one spray gun dedicated to spraying only clearcoats. There’s nothing more disconcerting than laying down a beautiful finish and when you start to lay down the final coat of clear, a glob of basecoat comes out and lands right in the middle of the clear. Having a dedicated clearcoat gun will eliminate this from happening. Of course, you can have the same thing happen with a glob of old clear from your last job if you don’t clean your gun properly. (I’ll go into that in detail a little later.)

But don’t think you have to have three guns. I know painters who have one gun with a 1.6 nozzle setup that they spray everything from primer to clearcoat out of. But it takes a little more time and effort to thoroughly clean the gun before spraying a different material.

Choosing Nozzle Setups

So what nozzle setups should be used for which products? Actually, you’ll achieve the best results when you refer to the paint manufacturers technical data sheets for that particular product you’re spraying. They’ve thoroughly tested their products and identified the best needle nozzle combination for each product.

A general rule of thumb is:

  • Heavy-bodied primers and primer surfacers work best when you use a nozzle size of 1.7 to 2.2.
  • Basecoats should be sprayed with a 1.4 to 1.6 nozzle.
  • Clearcoats should be sprayed with a 1.3 to 1.7 nozzle.
  • Sealers and single-stage urethanes should be sprayed with 1.4 to 1.6 nozzles.

Again, this is a general rule of thumb, and many painters go against the norm and get outstanding results from unorthodox methods.

Generally when you have a high-solids clearcoat or single-stage urethane, you should go down in nozzle size to break the material down into smaller particles to get a smoother finish. But some spray gun manufacturers go against this rule and go up in size – so be sure to refer to the gun manufacturers recommendation as well as to the recommendation from the paint company.

Primer surfacers require a much larger fluid nozzle. Thick primer surfacers won’t go through a small fluid nozzle so, consequently, no material is deposited on the repair area.

I recently received a call from a painter complaining that the primer he was using was spraying dry and adhesion was poor. He was using a very high-build product, but he said his body work wasn’t being covered and the primer was flaking off.

I asked what fluid nozzle he was using, and he told me 1.3. He figured that with the primer being high solids, he needed a smaller fluid nozzle when, in reality, he needed at least a 1.7 nozzle.

Understanding product and what’s needed to apply that product is very important, and many times problems can be attributed to not being aware of the basic fundamentals of choosing proper equipment for the product you’re spraying.

Air Errors

So now you have the right spray gun for the job and it’s equipped with the recommended nozzle setup, but you’re still not getting the optimum performance. Many times, this happens after you buy a new spray gun, especially if it’s a different brand from the one you were using.

What does this have to do with it, you ask? Plenty!

Maybe you don’t have enough air to properly run your spray gun.

“Come on. Give me a break,” you say. “My compressor puts out over 150 PSI. How much air do you need?”

Want to read more on spray guns? Then check out “Profit in the Paint Shop Series: Spray Guns.”

The fact of the matter is, PSI (pounds per square inch) doesn’t matter at all. The air consumption of a spray gun is measured by cubic feet per minute (CFM).

Air requirements for a spray gun can range from 2 or 3 CFM for a small touchup gun to as much as 18 CFM for some gravity-feed or siphon guns. The average for most popular guns is around 12.

If you check the output for most 5-hp compressors, it’s around 14 CFM max. Translated, this means that the average 5-hp compressor will efficiently run one spray gun of average air consumption. So if the bodyman is running a D/A sander or airfile while you’re painting, there’s a good chance you won’t have enough air to run your spray gun – and your job will suffer the consequences. Even though your spray gun may only use 30 PSI of air, it may exceed the CFM capacity of your compressor.

Other considerations are your air hose and fittings. If you’re using a 1/4-inch air hose, you’re severely hampering air flow and should consider at least a 3/8-inch inner-diameter air hose with high-flow couplers and fittings. This will dramatically improve air flow and efficiency.

Remember when you were a kid and you stuck a potato in the tailpipe of you buddy’s car, and it wouldn’t run properly? Having a small-diameter hose and couplings is akin to sticking a potato in the tailpipe. The gun is starving for air.

You Lean, You Clean

You knew I was going to get around to it. The next subject is cleaning. I know! I know! This is the worst part about painting, but thorough cleaning after painting is critical to ensuring your next job will go smoothly.

Most gun manufacturers include cleaning equipment with their spray guns, which usually consists of a round-barrel brush to clean the passages of the gun and the cup.

You need to remove the fluid needle and nozzle as well as the air cap after each use and thoroughly clean them. Flush the gun with fresh solvent after each use unless the material you sprayed was water-based, in which case, you should first flush and clean the gun with tap water, followed by gun-wash solvent.

Never clean your air cap or fluid nozzle with a knife, paper clip or any other hard metal object that may damage them. Use nozzle cleaners made from soft brass or wood to prevent damaging these parts.

How to Handle a Gun

The final step in achieving the best job possible is proper handling of the spray gun. Different painters have different techniques and operate at different speeds, but it’s important to hold the spray gun perpendicular to the surface of the car and to keep it at the proper distance.

Some painters don’t hold the gun perpendicular to the surface until they’ve passed the end of the panel. Toward the end of the panel, they tend to stop the gun and twist their wrist to point the gun to the end of the panel instead of moving their entire arm the length of the panel (much like a brush-stroke-type of method, as if they were painting with a brush). Because of this, the end of the panel does not receive the same even wet coat it would get from extending the gun the entire length of the panel.

Also, gone are the days when you could pour the reducer to your paint, hold the gun 12 to 14 inches or more from the surface and hose it on – since the reducer would allow the paint to flow and level.

But now, with HVLP technology, you need to hold the gun 6 to 8 inches from the surface to maintain control of the fan and of the material you’re spraying. This prevents dry spray and orange peel.

It’s a Guy Thing

OK, so maybe you want a new spray gun but don’t really need one. A little fine tuning to the one you have may well be all you need. And I’m sure your wife or girlfriend would think that money could be better spent at the mall or having dinner and a movie every weekend for a month or two.

They don’t understand. It’s a guy thing.

Writer Buddy Maule performs sales and technical support for a large supplier of automotive refinish products including, but not limited to, paint products. Prior to this, he owned a company involved in the manufacture of paint products.

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