How to Avoid Spray Gun Bounce-Back
George VondriskaDescription
The downside to most standard spray guns is that the bounce-back can be significant, sending excess finish airborne in your shop. Let George Vondriska show you why HVLP systems are the best way for the average woodworker to avoid spray gun bounce-back. A WoodWorkers Guild of America (WWGOA) original video.
I've been asked a couple times about the difference between conventional guns and HVLP guns when it comes to spray and finish. Both of the guns I have here are guns that will run off an air compressor. And one of the things I wanna show you is the bounce-back difference between these two guns. Now, in order to do this little experiment for ya, I've got 'em loaded with water, the water's got some food dye in it, some green food coloring, so that I don't have to wear a mask while I'm spraying. Make sure that whenever you're spraying, a lacquer, a polyurethane, shellac, any kind of finish, you're protecting yourself and your shop from the overspray. Now, here's what we've got going. I'm gonna hook a regulator up. First I'm gonna spray with the conventional gun. And the thing I really want you to watch for, is the amount of mist that rolls back off of my rosin paper here. I made it wet already so it's a little bit easier for you to see that mist as it comes back. Watch all of this stuff coming up off the top here, up here. If I were spraying a finish, that's all finish that would be getting airborne into the shop. Now, I'm gonna switch from the conventional gun to this compressor-based HVLP. Hold the gun the same distance from my target. It's just a kinder, gentler way to put spray on, to put finish on. There's very little mist coming off of this, compared to what we were getting from that conventional gun. The numbers on this are that with the HPL guns, you're getting about a two-thirds material transfer from this, compared to about a one-third material transfer from the conventional gun. So, we're getting a lot more of our finish onto the project, so we're saving some dough, also you're getting a lot less finish airborne that ends up all over your shop. So, clearly that compressor-based HVLP, or turbine-based HVLP are a great choice when it comes to efficiently getting finish on the project instead of all over your shop.
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I don't think that is a fair comparison. The spray settings for the conventional gun resulted in a too high pressure and material flow. Otherwise, the results would be the same. There are advantages and disadvantages of both types of sprayers, mostly involving clean up. The conventional guns are more expensive and you can't see when you are running low without opening it. The metal container is easier to clean when spraying oil-based enamel (thinned with lacquer thinner, NOT paint thinner or mineral spirits). There is always some material left in the sprayer container, hard to reach areas are more difficult and the spray head has to be spray-cleaned. The gravity-feed (GF) sprayers are cheap enough to have each one dedicated to spraying shellac, water-based acrylic (so-called "polyurethane") and genuine oil-based polyurethane. You can spray until you empty the GF container, you can even spray upwards, there is a built-in particulate filter in the sprayer that is easy to clean and the sprayer head can be easily cleaned by just running the appropriate solvent (DNA, water or mineral spirits, respectively) through it by gravity without actually spraying it clean - you can hold the trigger down with a rubber band, capturing the waste in a container. But waste enamel is very difficult to clean out of the GF sprayer head and the plastic container. I have a sealed room used for GF spraying. I never use it for spraying enamel due to the colored over-spray, preferring spraying enamel outdoors, weather permitting. But after spraying shellac, acrylic and especially polyurethane, there is a cloud of material in the room, so that there is always some over-spray to contend with.
I don't understand why one does the job better than the other. ?