Those few planes that I covered in silkspan, I sanded the open bays, but I sanded very carefully around the edges of all the ribs & spars -- any place where you have an edge in the surface is very easy to sand through, so you have to be exceedingly careful around them. This applies to any material you're painting -- I learned the "edge lesson" sanding out car paint jobs, then failed to apply it to my first silkspan job the first time around. I sanded the open bays freely in the middle of each bay, carefully up to the ribs, then I sanded the tops of the ribs with the paper wrapped around a finger, to try to hit just the top of the rib without putting any pressure on the edge.
The general idea is that you are putting a coat of paint onto a rough surface; the paint will smooth out very fine roughness to some degree, it'll contribute it's own roughness like a very smooth orange peel if you're spraying (or like a really rough orange peel if you spray too dry) or it'll leave brush marks, and it won't -- by itself -- smooth the 'long length' roughness at all.
Your job when sanding is to sand all of the high spots down to the paper and no farther. Once you've reached the paper in any area you must stop sanding that area until you've put more coats of paint on.
Note that this means that once you've put the paper on, you can no longer knock down the high spots with sanding -- you can only raise the low spots by filling them with paint. So you want to have all the high spots knocked down. Note also that it'll be easier to sand in the vicinity of the ribs after covering if you round the edges before you cover (note also that I did not figure out this lesson until after I covered my last silkspan-covered plane, and have waited 25 years to apply it!).
Topic: silkspan and sanding (Read 1766 times)