Over the years the public has been brainwashed into an easy shortcut for preparing exterior wood decks for refinishing. They have been offered gimmicks similar to the so-called "treatments" for the exterior wood preservation.
Were it suggested that an interior hardwood floor be first chemically washed to remove the old varnish and then a coat or two of polyurethane applied the advisor would be laughed out the door. That is because it is well known that the interior floor needs sanding to bare wood. This is the accepted practice for a durable refinish. It is the established method because doing so would result in a successful outcome.
On the other hand producers of so-called deck treatments offer deck washes as the means of preparing the surface for their treatment. Why should an exterior wood surface require less preparation than a more interior protected site? The reason is simple. None of these deck treatments are anything more than gimmicks designed to sell a next to useless liquid which by the manufacturers own admission must be reapplied semi annually or annually. Even then the surface becomes worse with the addition of more of the treatments. So to milk the sale to the utmost these purveyors of various kinds of deck junk add insult to injury by marketing chemical wood treatments. If they recommended sanding and the treatment went pot in the short time that it does, the customer would be more infuriated than when only chemical slopping on is suggested. For more detailed explanation go to www.rhinoguard.com and open the FAQ's.