Surprising amount of overspray

[Bob Gramann]

I started another discussion about my new toy to measure particles in the air a few weeks ago. Finally got to finishing a guitar, so I used the particle meter to check the air while I was working and to compare the overspray from two different guns. Here are my results. When I entered the room this morning, the meter read like this (the left is the .5 micron particle count in .1 cubic foot of air, the right is the 2.5 micron particles in the same sample).

I set up my spray fan and box. The two color filter is the one that David King suggested. It does pretty well catching overspray but not all that great catching fine dust.

Here is the complete spray box setup. The box is made from leftover building insulation foam glued together with silicone caulk. Under the guitar, there is a serpentine air path that puts the filters about 10 feet from the spray so that the overspray is dry by the time it hits the filter.

Even though it seemed that most of the overspray was caught by the fan through the filters and directed out the window, the air got dirty pretty fast. It wasn't visible in the room.

The air did not clear until I replaced the filters with a Merv 1900 furnace filter and ran the fan box in the room for about half an hour. After seeing this, I have been keeping my respirator on much, much longer (until the meter shows the low levels it did when I came in).

[Bob Gramann]

A friend told me that he had a new turbine setup that produced very little overspray, so he brought it over and we compared. He brought a 5-stage Apollo turbine and gun. It is a very nice package, sets up easily, cleans easily, and sounds like a large vacuum cleaner. My normal gun is an Asturo ECO/SX conversion HVLP gun running off of a compressor. We found that both increased the particle count in the room about the same amount, so there was no advantage to using the turbine vs the HVLP conversion gun for air quality. There was a difference in the quality of the finish (we shot Target EM6000 waterbase through each gun). Here is a coat from the turbine/gun combination on a fresh sanded surface. After several adjustments of pressure, fan, and volume, this was the best coat I could get.

apollosurface.jpg (8.25 KiB) Viewed 6787 times

After sanding the surface smooth again, here is a coat from the Asturo gun.

asturosurface.jpg (8.33 KiB) Viewed 6787 times

I am now much more satisfied with the gun I have. We theorized that the warmer air supplied by the turbine may have caused the finish to start to dry before it had time to flow out completely. Otherwise, the atomization seemed very good. Both guns had 1.3mm tips.

[David King]

That's a nice setup. The dust readings are crazy high. I never would have guessed but of course with the air going out at 100FPM it would be hard to notice.

[Clay Schaeffer]

Was the Apollo spraying a previously coated surface as was the conversion gun?
In my limited experience it does seem conversion guns give better atomization than turbine guns, but i'm not sure they give quite as good transfer ratios (material on the surface vs. overspray). But if you have to do a lot of sanding to make things smooth the end result might be the same.

[Bob Gramann]

In both cases, I leveled the previous coat with 320 paper on a rubber block. I'm prejudiced toward not having to do a lot of sanding. The quicker I can do a good job, the happier I tend to be. Now that I know that I have to deal with the overspray, that's what I'll do.

[Clay Schaeffer]

I don't know much about water based finishes. How do you "retard" the drying to get better flow out? Some turbine guns seem to need thin finishes to get decent flow out.

[Bob Gramann]

I'm using EM6000. I believe there is a retarder sold for it but I use the product straight out of the can. Since it works well with the conversion gun, I'm not going to start another learning curve when I don't have to.

[Clay Schaeffer]

I agree with you Bob. Too often people jump from finish to finish, and tool to tool, without really learning how to use them. I don't mind learning new things, but generally stick to the tried and true when it really matters.