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With Chris Curwen & Expert Auto Painter - Dave Gage (Car Cosmetics)

May 8th, 2007 - Issue 02

In this issue:

    * HVLP Spray Guns (High Volume Low Pressure) and the number one factor you must consider when purchasing a spray paint gun.

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It is recognized across the automotive painting industry that Sata, Sharpe and DeVilbiss are the three most popular brands of automotive spray paint guns.

A novice shouldn't have any problems producing great results using equipment from any one of these name-brand manufacturers. It would be a bit like playing your favorite vinyl records on a Technics SL 1210 MK5 Direct Drive Turntable, you're onto a winner every time!

For a full range of various spray paint guns and all of their accessories, take a trip to your nearest auto body paint and supply store. You will find that the prices will start from around $80 with the overall cost depending upon the brand and level of precision quality.

The paint cups are usually extra and will generally cost you $25-$40. In addition to paint guns, you can purchase air valves that attach to spray guns in-line with their air supply.

The purpose of these valves is to help you fine-tune the air pressure at the gun to perfect your paint spray patterns. We'll talk more about how to perfect your paint spray pattern a little later.

So what is the number one factor you must consider when purchasing a spray paint gun? Spray Gun Quality.

It's our advice to save up the extra money required to buy a top-of-the-line model than to settle for a middle-line unfamiliar import.

The problems with cutting corners and buying a cheap paint gun relate to inadequate spray patterns and trouble in finding replacement parts. You really need to take your paint gun purchase seriously and visit an automotive paint and supply store, always opt for durable quality instead of make-do availability.

Going back to my earlier example, you wouldn't want to play your favorite vinyl records on some old broken record player with a useless needle you bought at a flea market...of course not, you'd go to a proper electrical goods store.

Record players and paint guns are available at other outlets, however, a knowledgeable salesperson may not be.

By being in direct contact with a knowledgeable salesperson who has firsthand experience using the spray gun you are considering buying has some advantages:

You see, product literature may suggest a particular setting for inlet air pressure; while real-world experience can assure you that an alternative inlet air pressure may be necessary.

If you do not have access to this firsthand knowledge, your brand-new spray gun may NEVER operate as well as intended. Inlet air pressure settings are CRITICAL with HVLP spray guns, so it will be worthwhile to ask someone who knows for their recommendations, rather than relying solely on product literature.

Remember, what works and what works best may not be the same.

With conventional spray guns a typical air pressure of 60 psi or more is required. This quite high pressure blasts paint onto the surface with such force that over 65% of the material is lost due to overspray.

Additionally, the high air pressure is more likely to disturb existing dirt and debris and allow it to fall onto fresh paint causing a less than perfect finish.

Like we discussed last week, one viable means of reducing VOC and overspray pollution is by the use of High Volume/Low Pressure (HVLP) spray paint systems.

When HVLP spray paint systems were first introduced, they were composed of a spray paint gun and a turbine system that replaced the conventional air compressor. Although HVLP in theory made sense and was accepted as a working concept, the equipment was less than widely approved.

The new turbine system caused the air blasting the paint onto the vehicle to get too hot, causing the paint to dry too soon, sometimes even before it had landed on the vehicle. Turbine systems have since been redesigned so that they do not get as hot.

A more practical solution was the development of HVLP spray guns that can be used with conventional air compressors. This allows experienced painters to use a system that is more familiar to them and also makes the purchase of an air compressor easier to justify for the novice painter.

In addition, the conventional air compressor is far more versatile than a HVLP turbine paint system.

How HVLP works is by increasing the volume of paint that can uniformly pass through the spray gun's ports and nozzle, so that a relatively low pressure is all that is needed to propel the paint material out.

The end result is that more paint adheres to auto surfaces and much less is wasted through overspray via paint particles bouncing off surfaces at high pressure.

And the benefits of this?

Well, with the price of paint material alone being at what it is, the purchase of a HVLP spray gun will certainly pay for itself in a couple of repaint jobs, if not the first one.

Not only will you save paint material with a HVLP spray gun, you will see a great reduction in the amount of overspray, which should be of major importance to any part-time auto painter who is working in his/her residential garage or workshop.

It has been recommended for HVLP spray guns to use an air pressure of 10 psi at the tip of the spray gun. This is not to be confused with the air pressure at the inlet of the spray gun where the hose connects. It depends on the design of the spray gun but the inlet pressure may sometimes be near 60 psi to obtain the suggested tip pressure.

Let's go over the different types of spray paint gun:

SIPHON FEED - A siphon feed gun's paint cup is mounted below the air nozzle. This design requires more air pressure to siphon the paint material up and out of the cup. With a non-HVLP siphon feed spray gun, approximately 75% of the paint material ends up as overspray.

GRAVITY FEED - A gravity feed spray gun has the paint cup mounted above the air nozzle. This allows gravity to do the work for some of the air pressure, allowing for the use of a lower inlet air pressure.

However, on a non-HVLP spray gun, this will result in approximately 65% of the paint material ending up as overspray.

PRODUCTION GUN - If your painting is going to be limited to large body panels, such as doors, fenders and hoods, a full-size production gun will suit your needs. Commonly having a one-quart paint cup, this gun can spray a fair amount of material before you need to refill.

DETAIL GUN - The difference here is manoeuvrability. Detail guns are perfect for intricate painting jobs, like small touch-ups requiring fine spray patterns and door jamb painting.

We'd like to end this weeks issue by covering a little on spray gun control and test patterns:

Paint companies recommend specific spray gun setups for applying their products with. This would indicate a specific fluid tip and air cap that should be used with the particular paint product that would be available from the dealer of the spray gun.

This is another reason why you should purchase your spray gun from a paint supply store instead of from a tool store that sells a variety of tools without servicing any of them.

These settings are available from information sheets and application guidelines or from your auto body paint and supply worker who may have firsthand success using a particular spray paint gun setup.

Most full-size production spray paint guns have two control knobs located on the upper rear section of the spray gun housing. These control the volume of paint that exits the nozzle and the airflow or fan spray.

Material control is usually adjusted by the knob that is in-line with the air nozzle, whilst the airflow is adjusted by the remaining knob.

Refer to the literature included with your spray gun or ask your paint spray gun supplier if you have any questions regarding adjusting or cleaning your spray gun. (We'll be covering how to clean your paint gun in our next issue.)

This is yet another reason for purchasing a spray gun from an auto body paint and supply store instead of from a general, discount store. A properly adjusted spray gun will give you professional results and will last a very long time if you clean and maintain it correctly.

Now, you are going to have to practice in order to learn how to make proper spray patterns and volume, this is important. Various paint products and their reduction ratios will spray differently, especially with different recommended air pressures, so get hold of an old panel and use it to perfect your skills.

Many painters keep test panels in their spray painting area or they use sheets of wide masking paper taped to a wall, either will provide you with an excellent medium in which to practice and/or test on.

Our advice is to spray paint onto the test panel and then make adjustments to your gun in order to get the right pattern and volume. Never start the actual painting until you are sure you have the correct setting on your paint gun.

Occasionally, during your paint job, you may notice a defect in your gun's fan pattern. To check it, turn to your test panel and shoot a clean section with a blast of paint. If it doesn't look right, check the controls and the air pressure.

If the pattern is still flawed disconnect the paint gun from the supply hose and clean it thoroughly. The chances are that a small port or passageway has become clogged and must be cleaned before you can continue spraying paint.

As you move around your vehicle the surfaces that require paint are never the same for long and at times become more confined or difficult to reach, as on some front end sections.

In these instances, you must reduce the air pressure or change the fan spray to hit the smaller areas. You can make these adjustments again by practicing on your test panel.

Finally, holding racks are very useful when painting separate sections of dismantled bodywork as shown in How to Paint a Car - The System. These racks are designed to tilt and adjust for the part that needs to be painted.

They are commonly used in body shops but possibly too much of an investment for the average person painting their first vehicle. If you get lucky enough to find a second-hand rack still in great condition, it could turn out to be a very useful tool to add to your collection.

Check with your auto body paint and supply store; they may be able to point you in the right direction for getting hold of one.

If you can't get hold of a rack then you could try making your own, failing that make the most out of lying down or hanging up the parts to be painted.

You will need to place them so that you can comfortably access all of the part(s) for painting. This won't always be possible but do what you can to make your life easier. After you feel you have painted all of the surfaces, take a second look at it from various angles to make sure you haven't missed anything.

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That's all we have for you this week. Thank you very much for reading. We both hope this issue has been of valued interest to you.

Next week we'll cover how to thoroughly clean your spray gun after each use so that your gun will provide you with a uniform spray pattern every time you use it and we'll also include spray gun manoeuvring.

Happy Painting!

Chris Curwen & Dave Gage
www.LearnAutoPainting.com