I remove the old and lay in some new. Have been very happy with the product (I pretty much exclusively use Sikaflex whenever I use caulk), and I like the look. I started out years ago with a fairly small bead, maybe 1/8" to 3/16" or so. Now I am bigger, maybe 1/4". I tape both the toenail and the deck and I smear it in there. Cheers, John