I am sanding some very old , 50 plus years, 12" wide barn wood that was used for a floor. It is pine and one inch thick.
My attempts to sand it both with rotary and belt sanders have been an expensive exercise in clogged sand paper.
Starting with 36 grit, the surface of the paper quickly becomes clogged with a brown substance that is very warm to the touch, then cools quickly to a hard solid surface.
It does not come off the sand paper and clogs the paper after only a few square feet.