Yes that is a floor sander working on this deck. 36 grit paper to level any board cupping. Finish sanding is done with 60 grit sandpaper, yes 60 grit as the finish sanding. The objective is not to create a polished furniture finish, but to open up the grain of the wood so that it will accept the finish, allowing it to stick for a long time.
John Gaston of Pleasantview Wood Restoration Systems in Bracebridge, Ontario shows the professional way to restore a deck. His preferred finishing formula is a slight modification of a commercial product.
He cleans off the deck with stripper chemicals and power spraying. Then he rough sands it to open up the grain. Then the finishing starts.
50/50 Cetol 1 and Cetol DEK
WEARCOAT (1 week later)
Cetol is made by Sikkens and is available in many paint departments.