Looking for comments on the pros or cons of sanding the last coat of primer.

 I intend to fly in primer for a few months and have mixed feelings about sanding the primer to make it slipperier. I've heard that it should be wet-sanded with 320 and also that it's better not to sand it as opens up the primer to absorbing moisture and dirt.

 

John,

 

IMHO, don't sand.  This will make the preparation for paint much easier since cleaning and finish sanding could be better for the paint process.  If the sanded primer is a two-part epoxy it should not absorb moisture, dirt or oil but the early sanding could make the final cleaning/prep harder.

 

Side note:  I flew for 1.5 years in sanded WLS primer and it was hard to clean before painting.  Also, I had Krylon-painted numbers on the primer that, while it was easy to clean off with acetone, resulted in a slight raising of the primer area under the numbers, but that disappeared after about 4-6 months post painting (PPG base coat, clear coat).  If I had to do it over again, I would have had the painter put on another coat of primer just before painting.

 

Also, the sanded WLS primer generated a good deal of skin static during flight and that went away after painting.

 

I was glad I flew in primer because I had a number of experiments (trim tabs, cowl modifications) that required skin changes (i.e. they didn't work as planned).