Penetrating water repellents do not peel, but they wear out. When it is time to re-coat the wood, you do not have to scrape the wood clean prior to applying the new coating. This can save a tremendous amount of work. You will still have to carefully and thoroughly wash all areas and then do what is necessary to apply the coating of your choice. Scraping or stripping loose films should be done prior to washing the wood with your method of choice.