Michael Dresdner: The panels you refer to are made by a number of different companies in several countries. Some are made using exterior glue, and some are not. That, alone, controls whether they will hold up or delaminate outdoors. No finish or treatment you can add will effectively make interior adhesive survive outdoors. Ask for the specs on the panels sold at your store, and while you are at it, also check what type of wood is used, since some woods are more prone to damage by bugs and decay than others. That, too, can spell the difference between boards appropriate for outdoor use and those that are not.