The best method of protecting plywood decks and superstructure is to sheath them with fibreglass or Dynel cloth using epoxy resin.   Polyester resin can be used but, if you want the best long lasting job then, epoxy is the way to go. We have used polyesters for many years with satisfactory results but, when there is a better product that is not too much more expensive, why not use it. Generally speaking you need to use two or more layers of sheathing set in epoxy resin to get the best results. Two layers of cloth weighing 18 oz per sq yard or 500 grams per square metre would be about right. Larger boats say those over 36 ft or 11 m on deck, may benefit from additional layers of glass. 

    Before starting to sheath plywood decks and superstructure, you should fill all nail and staple holes and any other blemishes.  All holes should be filled flush with the face of the plywood and all corners must be rounded to accept the fibreglass.   Use a filler, compatible with the resin you are using, to create a radius for the fibreglass sheathing to smoothly progress from cabin sides to decks, coamings to decks and anywhere else that it is required.

   After you are satisfied the decks and superstructure are ready to accept the fibreglass sheathing, give the whole area a coat of thinned resin and allow this to cure before proceeding with the sheathing.

   Any excessive moisture content in the plywood will prevent you achieving a lasting bond between the fibreglass and the plywood decks and superstructure so be sure that the plywood is dry and the humidity level acceptable.  

   Even if you plan to install a laid fibreglass deck over the plywood, it is still advisable to install at least one layer of fibreglass between the plywood and the laid timber deck.   A fibreglass finish will form an excellent seal for the cabin sides and other areas where there is no laid decking.   If you follow our advice on the above matters, you should have a totally waterproof deck that will last indefinitely.  Once the sheathing is complete and the resin has cured it will be necessary to apply a non-skid finish to all horizontal surfaces. This can be achieved a number of ways already mentioned in the fibreglass chapter.