SHERLOCK HOLMES AND THE CASE OF THE CONTAMINATED PAINT
When the FAA approved the “experimental category” of aircraft and agreed to allow people to build and fly their own airplanes, part of their justification was the “education” the builder would get from the process of constructing a plane. In their infinite wisdom, they believed this was a good thing and could benefit society as a whole. After all, we want our citizens to be smart. Well, if education is a good thing, I got a whole bunch of it when I started to paint my wings two months ago.
The wings were already in silver primer. My task was to paint my stars; white on a blue circle with a red meatball in the center and then add the yellow to the rest of the wings. I had already completed the paint on the fuselage, including stars, so this would just be a repeat of the process.
With the first set of stars masked off I began shooting paint. But what was this? Tiny craters about the size of a pin head all over the place….maybe a quarter of an inch between. Hmmmm…I thought, it must be the thinner I used to prep the surface. Perhaps solvent pop coming up through the paint. So those stars were sanded off, a careful prep of the surface performed, and another shot of paint. There they were again! That sanding is a real drag so this time I grabbed the thinner and some rags and started wiping. Something was definitely wrong here. So instead of using my masked star areas as a testing ground, I started shooting samples. It must be my air supply I thought.
Oil or water from the compressor can cause problems, so with a better trap I shot again. The pesky craters were still there. An alternate air source produced the same results. Now my suspicions turned to contamination. Silicone has a reputation as a nightmare for catalyzed polyurethane paint. It is thick in Armorall, and there is some in WD-40 and Pledge and other stuff. Just the presence of it in your shop can cause problems. And it is used in mold release. I learned that the spray gun I was using was previously used for spraying mold release. Aaargh…there is the source of the contamination. A thorough cleaning of the gun should solve the problem, but no luck. But than I was told by experts that once a gun is contaminated you can never get all of the silicone out and the gun needs to be replaced. After using three different guns and two different air sources, I concluded that the gun was not my problem.
Next I turned my attention to the paint. I must have spoiled paint; after all, my hardener was over a year old. So with a new batch of paint in hand and high hopes, I shot again. Aaargh…the craters were still there. So now I started becoming very intimate with my paint supplier. My entire history of the problem was recounted. They were very helpful and sent me home with a half gallon of paint that was left over from a project they had just completed. So they knew the paint was good. They also sent me home with sterile metal pieces to test on, and also their brand of surface prep thinner, which of course is the best you can get because it is what they sell. With all of these supplies in hand, a perfect air source and a known uncontaminated gun…..I tested again. Aaargh….more craters.
At this point I was running out of things to try. I decided to take the gun and air supply out of the process altogether. I simply brushed on small quantities of mixed paint. I still had craters. I tried another brand of polyurethane paint…still there. Altogether, I used four different paints. Okay, more internet research gave me more ideas to try. It seems that silicone can travel airborne and infect paint in other rooms. I scoured my garage for contamination. Nothing was apparent. However, further research showed that some under arm deodorants contain silicone. I ran into the bathroom and checked mine. Sure enough…there was silicone! This has got to be it I figured. I was the source of the contamination. So I jumped in the shower and scrubbed my armpits for ten minutes. Feeling fresh, very clean and uncontaminated, but a little tender under the arms, I returned to the garage. Another small mix of paint, another brushed on test patch and aaargh….still the craters. What else could I try? There was nothing left. Hmmm, perhaps my pores were too deeply embedded with the stuff. So I had Marian mix up a batch for me and brush some samples. She uses a different brand of under arm deodorant. I anxiously awaited the results and then…aaarrgh…still the craters.
I went home dejected.
It had been six long weeks of experimenting and I had tried everything. There was nothing left. I sat down in my favorite thinking chair, which coincidently is my favorite napping chair, and I thought, and thought. I went through everything used in the painting process. Could it be the brushes, the stirring cups, the stirring sticks, the measuring syringes? These had all been verified in the last six weeks and ruled out. They had all been used before on my fuselage. The paint store uses the same stuff including the measuring syringes. They buy them from a veterinary supply. Hmmm, what about those syringes? But I used them before on the fuselage. I get them at Big R. And than I remembered, about a year ago they changed there supplier on their syringes. Could that be it? I jumped up out of my favorite thinking chair and went to the garage for another test. I anxiously mixed up another batch, using measuring cups, and then began brushing. What this…NO CRATERS! Hmmmm….I brushed some more patches…..still no craters. I brushed and brushed…this couldn’t be true…no craters at all! I loaded the last bit of paint in my gun and began spraying test patches…still no craters. This was it! There must have been silicone in the syringe, perhaps as a lubricant for the rubber seal. We all assumed they were sterile. After all, they are for dispensing medicine to livestock. I guess a little silicone won’t kill a cow, at least not before they are shipped to the slaughter house. Actually, silicone is not hazardous to people or animals, just polyurethane paint.
So in the words of Sherlock Holmes, if you remove everything that you know cannot be the suspect, whatever is left has to be it. I always said the solution would be the last thing I tested. I was so happy with my success, I felt like going out and getting drunk. But instead, I prepped two stars on the left wing for painting. I loaded the paint gun and shot two perfect stars. My elation from achieving a good paint application, (and perhaps a bit of a buzz from the paint fumes), were all I need to end the evening feeling really good. And just like the FAA planned, I am smarter from the whole experience.