ORIGINAL: NM2K
I try to remove as much castor oil as possible via an infra lamp (closely monitored to prevent fire) and paper towels. The towels are used to blot the oil that will come to the surface of the balsa.
After the blotting ceases to yield much oil, I then spray on a medium coat of C2R cleaning compound, meant for upholstery and winter jacket cleaning. This stuff will dry to a white powder. Carefully clean away the powder, then reapply another coat of C2R. Do this until you can make no further discernible progress. After this treatment, a light coating of Balsarite is justified. Then recover with fabric or plastic covering. I know this technique works for a fact because I have used it on several of my planes with excellent results.
Ed Cregger
Thanks!