It's the tautening kind.  Could make your rocket spin.

I was thinking that would happen, may just stick with Brodak Nitrate.  On my test pieces of balsa the Nitrate unthinned from Brodak actually filled the grain in 3 to 4 coats, same as the Brodak Balsa Sealer.  I have noticed that the balsa is smooth until I hit my first coat of primer.  After I spray a coat of primer there is no deep grain showing but more of grain popping up......Any ideas what causes the grain to pop up when priming?

    You put more solvent back into the dried primer, that causes it to expand, and when it shrinks back, it shrinks back more in the pores. And presuming  you started this experiment a few days ago, another issue is that 2-3 days is *nowhere near* enough time for the shrinking stabilize, so if you sand it flat after, say, a day, just letting it sit for week, all the grain will come back out, because it is continuing to shrink. Nitrate is generally better about this than butyrate, but realistically, you can't make it flat and expect it to stay that way unless you wait *weeks to months" before sanding it and rubbing it out.
 
     Brett