I'm not quite sure what you mean by "compost board".
If you are talking about composite boards for a deck, decks by design are supposed to shed water between the boards whether they are composite or wood. If you want a deck surface that is sealed and only sheds water to the edge, you would need to consider an outdoor weatherproof surface like Duradeck or something similar.
A forum community dedicated to Do it yourself-ers and home improvement enthusiasts. Come join the discussion about tools, projects, builds, styles, scales, reviews, accessories, classifieds, and more! Helping You to Do It Yourself!