Process Makes Perfect

After about 2 days of drying, my freshly-primed parts for the horizontal stabilizer started showing spider lines in the paint, then flaking off and looking like this horror:

It took me a while to figure out what went wrong, but it looks like I failed to properly clean the parts before priming with SEM Self Etching Primer. I had been using the Simple Green Extreme precision parts cleaner to clean and de-grease, then drying the parts with a clean towel. Here’s where I went wrong – after this step I went right to priming. The important step I missed was to rinse the part off with water, to remove the cleaner from the surface of the part. Going through a Google search, I also learned that a lot of people do a final cleaning with acetone or isopropyl alcohol right before priming.

Check out my Process page for details on my revised priming process – which I can confirm now works successfully.

Mercifully, I’ve been able to fairy easily remove all the primer from the affected parts using the Simple Green cleaner and a Scotch Brite pad – still a lot of work though. I got through about half of the HS parts tonight, will have to finish tomorrow.

After following the 9 steps above, I re-primed one of the parts (a plate) and the finish came out much better. On the left is a part that I stripped back down to the bare metal, and then cleaned with the new process. On the right is a part that was reworked and was sprayed with 3 light coatings of primer. Tomorrow I’ll do a tape pull test to make sure the primer adhered properly.

I work in engineering so I know how important it is to have your process right, especially when it comes to applying coatings to metal. Lesson learned – do a test of your process on a scrap part first to avoid having to rework a bunch of parts like I did!

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