Sikkens specifies that it's finishes (which I consider to be films) must be applied at below 19%. The FPL did some studies and found that applying finishes to wood with any weathering greatly diminished their life because the finish is applied to damaged fibers.

might be something of interest in their finishing techlines;
http://www.fpl.fs.fed.us/products/public...amp;unit_id=TMU