That's a new one to me. I've never removed the old planking prior to cold-molding nor have I ever heard of anyone else doing so. Standard practice is to take a saw or router to open the seams to a uniform width and the glue wooden splines into the seams. These are then faired to the hull .To address the added weight issue, many plank on frame boats that have been cold molded do not gain weight because they lose the weight of the water that is no longer saturating their planking. The hull is thoroughly dried out prior to sheathing and the inside of the hull is sealed in a proper job. Progress on one such job can be followed at Welcome to the Colonial Seaport Foundation, Hampton, Virginia
as they convert an old 47' Rosborough Privateer gaff topsail ketch into an 1800's style Colonial Sloop. The work is being led by John Collamore III , who has performed this process on many old classics which would have been dead otherwise.