The Exciting Adventures of Pin Hole Filling, or How To Make It Snow in Your Garage in Ten Easy Steps

George Gennuso

Originally published August 1997

As you know, I excel in making it snow in my garage, not just with wing profiling (micro balloon dust) but NOW with pin hole filling dust!!! And I have come to this conclusion: Anything done to a composite airplane that involves friction creates snow......

I have used many, many products to fill the pin holes on my Pulsar, and didn't like any of them for one reason or another. I won't use brand names, but ask me and I'll tell you. Last month on the internet Pulsar newsgroup one of the users said he had heard of a new product called Smooth Prime made by Poly Fiber. Smooth Prime was supposed to fill pin holes with out the use of putty knifes and spreaders, just spray it on and sand it off and the pin holes are filled. And it was Non-Hazardous. You guys know what I'm thinking, another opportunity to spend money on the airplane..... I called Poly Fiber and ordered a gallon. I also had to buy a new HVLP gun to go along with the Smooth Prime (Jim Piavis whispering in my ear) to put it on with. Everything arrived and I decided to start with the horizontal stabilizer.

The Task:

When the Smooth Prime arrived it seemed like the can was awful heavy, so I called Poly Fiber and said that the can was pretty heavy and asked how much it weighed per square foot once it was applied. The Poly Fiber guy said that it was water base and that it was the water that weighed so much; once the water evaporated it didn't weigh much. So I asked again how much does it weigh once applied, being very weight conscious just like the rest of you guys. He said the product was so new that they didn't have a spec on it yet.

I was still worried about it being too heavy even though it would fill pin holes easily, so I decided to find out for myself on the horizontal stabilizer. I used West System and micro balloons to fill the seams and imperfections and then sanded it smooth in preparation for the Smooth Prime. Then I made a short trip to Vons Grocery store and persuaded the Deli person to weigh the stabilizer. It went something like this: Let me have a pound of bologna, some of that potato salad, four of those rolls, a half pound of Swiss cheese, weigh this stabilizer, some of those pickles, etc..... Anyway, I got it weighed on an electronic scale that went to hundredths of a pound. It weighed 5.53 pounds.

I got everything set up. This consisted of washing the part with an alkaline cleaner (409 works) and then drying it off and wiping it down with rubbing alcohol. Poly Fiber recommends that you thin Smooth Prime with water (Geeze, the thinner for this stuff is cheap!) 4 to 1 and spray it with a needle and nozzle rated for urethane paint. I mixed the stuff up, put it in my new HVLP gun, and laid down a beautiful coat of Smooth Prime on the stabilizer. Well that's the way it was supposed to happen. What really happened is that 10 pounds of pressure was not enough to get it to come out of the gun. I didn't want to thin it any more because then it wouldn't fill the pin holes.

Plan B: I switched to my High Pressure gun and at 35 pounds of pressure it sprayed nice, but the stuff dries so fast that I couldn't get it to flow out. I got a lot of orange peel on the surface. Smooth Prime dries fast--you can sand it in half an hour. I sanded the first coat and 70% of the pin holes were filled. Incidentally, it sands good wet or dry. I picked dry because, you guessed it, I love that white snow, but also because wet sanding turns that white stuff back into paint that drips down and stains the garage floor (it's just about all cleaned up Diane, honest....). I shot another coat and tried different air pressure, spray patterns, distance from the surface with the same results, lots of orange peel. Sanded that one down and had 90% of the pin holes filled. I forgot to tell you that I purposely left some large air bubbles unfilled to see if Smooth Prime would fill them; it did. Next I tried a brush--didn't work. I got lots of streaks and a lot of sanding to get them out. All of the pin holes were filled on the stabilizer so I went on to the elevator. But first I went to Home Depot and found some really nice foam rollers about 6 inches wide. Did all of the same prep but decided to try the roller. I found this to be the best way for me to put Smooth Prime on. An added benefit was that the roller forced the Smooth Prime into the pin holes and it took less time to fill them and there was less wasted filler.

The Results

Now the big question was: How much does this stuff weigh? Went back to Vons and asked the Deli person to weigh it for me. Different Deli person--she thought I was nuts (well, maybe). So, smooth talker that I am (and 5 pounds of cold cuts later), she weighed it. It now weighed 5.91 pounds. It picked up .38 pounds. I was kind of surprised--I didn't think it picked up that much weight. I sanded it down until it was translucent so there wasn't a lot of Smooth Prime on it. So, back to the garage to do some math.

The stabilizer has 1622.8125 square inches of surface. That equals 11.269531 square feet. The additional weight (.38 pounds) divided by the square footage (11.269531) equals the weight of Smooth Prime per square foot which is .0337192. I think that this is acceptable, but I have no frame of reference when it comes to these things. This is when I ask Russ Erb if he will help out and let me know if other fillers and primers weigh more, less or about the same. (Notice how you can get the other chapter members to help you if you write something for the News Letter.....) (I asked Brian Martinez and Norm Howell. Brian's only response was "Tell him to sand all of the filler off in any case. The only filler you want is that which fills the pin holes." To Roy Bailets: Any inputs?)

Anyway, I think this is a good product. It is very easy to fill pin holes with (as compared to other fillers and methods) and I plan to do the whole Pulsar with it unless Russ comes in yelling and screaming "Don't do it, Stop you Fool". (Wait! Wait! But what about...oh, never mind. Go for it--and let us know how it goes. Now, how can I sell foam rollers from Home Depot to Jon Goldenbaum of Poly Fiber at a grossly inflated price--call them "aircraft grade"? Hmmm, maybe...) If you want any more information about Smooth Prime or want to see what it looks like, just ask me! Even better, if you want to put it on and sand it off, COME ON DOWN!!!! I would be glad to show you how to do it. What's a little more snow?


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URL: http://www.eaa1000.av.org/technicl/pinhole.htm
Contents of The Leading Edge and these web pages are the viewpoints of the authors. No claim is made and no liability is assumed, expressed or implied as to the technical accuracy or safety of the material presented. The viewpoints expressed are not necessarily those of Chapter 1000 or the Experimental Aircraft Association.
Revised -- 18 October 1998