I have drilled small holes around the soft areas and then from the lowest hole injected epoxy into the area. Using the lowest hole insures that i will not get a "drain effect' and therby lets the liquid be forced into all the voids. I just did this a week ago and the deck is noticeably firmer now. make sure you tape the injection hole over after the treatment or you'll get a nice little piece of epoxy flow artwork on your deck.