HVLP & Orange Peel

[Harold41]

I have an older conventional siphon feed gun that did OK on the last car I painted (about 10 yrs ago) & I've used it to paint several other things since. It was the top model Craftsman when I bought it in '92 or '93, rated for 10 CFM @ 40 PSI. I have a 41 Chevy Truck to finish and a 52 MG to start soon plus I have 10+ pieces of outdoor furniture to paint soon. I thought I'd upgrade to a better gun with HVLP to get better transfer efficiency. I was thinking of ordering a Sharpe FX300 or one of the Astro HVLP or LVLP guns. I decided to call the local paint store to see what they had. The guy there says that most HVLP guns give lots of orange peel unless you turn the pressure up above the HVLP level. He says to get good (no orange-peel) HVLP you have to go to a SATA or IWATA. Am I just as well off with my conventional gun or is he not a good painter? And will these guns do what I need or should I go higher?
Thanks, Harold

[Phil V]

Harold, it all depends on what type of paint you plan on spraying. If you plan on using lacquer or acrylic enamel on your projects then that Craftsman gun will probably work fine. ( If I'm thinking of the right gun then Devilbiss made that gun for Sears, and its not the Finishline series gun).

If it is your plan to spray acrylic urethane in single stage or basecoat/clearcoat then you will need a spray gun designed to handle that type of paint. You Craftsman/Devilbiss was not designed to handle that type of paint. I have never used the Finex guns so I can't offer advice either way, although Sharpe makes excellent spray guns (I've owned a couple of them, not the Finex).

[Len]

Your jobber is right to a point.... If you're going to go HVLP don't go cheap. There are several good HVLP guns but none of them are the inexpensive ones. While Sata and Iwata are good so is DeVilbiss, Dura-Block and a couple others but none under $300 that I've seen atomize real well. However there are several "reduced pressure" guns that atomize very well but are still not inexpensive guns.

Your old conventional gun uses high pressure to atomize paint but the high pressure causes side effects that are harmful to the overall operation. Whenever you spray your air causes a "pillow" or cushion of air on the surface being sprayed, this pillow is more dense and higher with high pressure than it is with lower pressure. The more dense pillow causes the atomized paint to bounce off and thereby lowing your "transfer efficiency" and generating more overspray. Older and inexpensive guns can have as little as 30% of the paint reaching the surface while newer HVLP and reduced pressure guns have at least 65% of the material reaching the surface.

Another (more important) feature of reduced pressure spraying is the increased control you have over the result. With less pressure the air pillow becomes softer and lower but it also jumps around much less than high pressure spraying. While spraying your gun is constantly changing the angle at which the air hits the surface which causes this air pillow to move from side to side and up and down. With high pressure this pillow jumps much faster and much further than it does with lower pressure and the result tends to be an inconsistant finish having more runs and dry spots than with HVLP and reduced pressure guns. This is particularly problematic if the painter is a novice and/or doesn't paint regularly because they don't have the control that a professional painter will have. I always felt that HVLP and reduced pressure guns are most beneficial to the DIYer because of the increased control, less overspray and less material usage. However you can't go cheap with this technology and expect the best result. From my experience you can't expect the same engineering from gun costing under $100 than you get with one costing $300 and up.

As far as getting the most for your money I'd recommend the DeVilbiss GFG-670G reduced pressure gun. This gun sells for just under $300 and atomizes real well and still has good transfer efficiency. You don't want to forget that atomization isn't the only important feature of a spray gun and, if you intend to sand and polish the paint then the orange peel texture left by your spraying is much less of a problem because it disappears in the final stages of the work. It's more important that you don't generate runs and dry spots because they are much more difficult to repair properly.

DeVilbiss GFG-670G Link

[Harold41]

Thanks Len, Exactly the advice I was looking for.
HLW

[Lost in NJ]

Len,

Just curious why a novice should use the Plus over the GTI-620.

Isnt the 620 a true HVLP, what characteristics makes it less favorable to a novice?


The whole idea of which gun is a better selection is a tough one. I have been trying to figure out which one would be best and I am having a hard time learning the true technical details. I have looking at several sources trying to understand which guns are real HVLP and which are the Plus type reduced pressure and then match each type which paint they spray best. The answers are all over the place and hard to nail down.

I am hesitent to buy a $300 gun as I do not know which one would offer the best performance for my situtuation to justify the 'risk' of buying one. My primary paint I use will be Concept single stage. I am also wondering if I can get away with using a big gun to spray small parts or if the overspray would cause too much loss of paint to be a good idea. Of course, part of the reason for buying a pricey gun would be to reduce the amount of paint needed to do a project. I also have some decent surface area left with four fenders and some other sheet metal so I need a big gun.

The other part I toss around is getting a better rated $150 gun like the durablock and know I am doing better than the older finishline III gun I have with a plastic fluid tip. I have to question in my mind if I can really improve the lay down of the paint by spending the extra $$$.

I know these are tough questions. But I have been looking at all the different brands trying to understand where the differences lay and how each on my help me. In about a month or two I will be doing finish paint so I still have some time.

Thanks

[Len]

There are basically three types of spray guns that should be considered when purchasing this type of equipment.... conventional, HVLP and reduced pressure (RP).

Conventional is the older technology that most of us were using 15/20 years ago. These guns atomized well but had lousy transfer efficiency and lacked the control brought about by lowing the pressure.

HVLP came about because of the laws requireing greater transfer efficiency. When HVLP first hit the market there were no "good" guns but then eventually the engineering improved and now there are several good HVLP guns on the market but when purchasing HVLP you need to watch that you don't try to go with one that is too inexpensive because the engineering is usually lacking and many low-end HVLP guns won't do a good job of atomizing and can have an uneven spray pattern. For a gun to be HVLP it must have two characteristics... 1. Pressure measured at the air cap must be below 10 PSI and... 2. It must transfer at least 65% of the material to the surface being sprayed.

RP (reduced pressure) guns are the latest innovation by the spray gun manufacturers. This type of gun has a higher pressure at the air cap so it doesn't qualify as HVLP but it does have a transfer efficiency above 65% and qualifies as a legal gun in those areas where spray guns need to be "compliant" in order to be used professionally.

Conventional gun are more difficult to opperate than HVLP because of the high air pressure at the cap but they do atomize well and allow the painter to apply the coatings quickly. HVLP is easier to control but doesn't atomize as well as conventional. Reduced pressure atomizes well, is faster and has better control than conventional but it's usually not as easy to control as HVLP.

For the beginner the HVLP is probably the best bet because of the control is allows but while the finish may have fewer runs and dry areas it may have more orange peel and need more aggressive color sanding and polishing to get the desired result. The RP is a good in-between gun that gives good control but also atomizes well.

The DeVilbiss GTI620G is an excellent HVLP gun and is one that I highly recommend for novice as well as pro painters. The DeVilbiss GFG620G RP gun is the latest version a little faster and atomizes better but is a little trickier to control because of the higher pressure at the air cap. I personally feel that the GFG is a little better gun for the money because it's the latest engineering but both guns are excellent performers.

Of course there are other guns that I could also recommend but this is my take on the DeVilbiss GTI/GFG guns.

[Lost in NJ]

Now that is the kind of information I have been looking for.

Thanks!

Can you expand this include other brand guns? I am not stuck on Devilbiss, they just happened to be easy to compare in my question.

[Len]

Most of the high-end guns are good including Dura-Block 007, Sata RP and HVLP, Sharp T1 etc. It's when you get to the lower priced options that many products need to be picked carefully. The reason I like DeVilbiss is that their products are well know around the world and you can get guns and parts just about everywhere at a reasonable price. It's guns like Iwata and Sata that you could have problems getting parts after you've spent a lot of money for their guns.