Actually, doing it board by board is going to take a lot of time and a lot of space. It takes a number of hours before it can be handled, that is the Penofin I am talking about. Just make sure to seal the ends with wax, then when you are done, finish off with Penofin. You usually apply heavy and then wipe off after 15 to 20 minutes. If you leave it on and don't wipe it will be sticky and take a few days to cure and won't look right. Don't wait too long because the board will grey after a few weeks. Of course you can always sand them down and they will look brand new but why go through the extra work. Finishing off the bottoms is really unnecessary IMO. Ipe will last forever, even untreated. Treatment is mostly to bring out the beauty of the wood unlike some other decking materials.