After several weeks of blowing dry fir needles to the side of the road and bagging dry leaves I looked under the deck, expecting to scrape and clean... surprise! The underside looked like it had been bead blasted. Never noticed before. Is this the action of the sharp pointed needles and crushed leaf stems ? Anyway , very welcome. We know that sand blasters use walnut shells for mild surface prep...HMMM? Maybe I should bag and ship worldwide?