Deck Protection Decks, easy, one time, permanent protection

I used your product about a year ago on my outside redwood and Alaskan yellow cedar decks and it worked great, two questions, do I need to reapply the product over time, and I want to spray the joists under my upper decks, the pressure treated lumber is now about 4 years old so I think the product will work fine, would like to just use the garden sprayer again, do I just wet the underneath of the upper deck and joists and just spray, I assume the lower deck needs to be wet so that any dripping doesn’t stain, correct or not let me know, thanks.

Ken in Moss Beach, California, oh yes no mold no mildew for the first time in 15 years on our decks, yahoooooo.