Plywood

"I hope someone can help me un

"I hope someone can help me understand this question. I rebuilding a pontoon with a MC Sterndrive.

What are the real differences between Marine plywood and Treated plywood? The basic, not the upper grade Marine plywoods that have single sheets of plys etc.

Also has anyone any experience with some of these synthetic plywoods?"

"Larry:

Marine grade plywoo

"Larry:

Marine grade plywood is made of wood plys free of knots and cracks and exterior glue, thus the extreme price.

Treated plywood is not sealed and will hold water; don't use it.

Synthetics are overpriced; never used them.

If you are replacing your deck, use 3/4" exterior grade basic plywood w/1 smooth side that's not perfect since it will be covered w/carpet or other flooring. Cut the wood to fit first then treat the wood w/2 coats of CPES (Clear Penetrating Epoxy Sealant) on both sides and ends. The fumes are nasty so do it outdoors and let cure until most of the odor is gone. If there is wood attached to the frame to connect the floor, replace with CPES treated wood of the same.

When securing the floor to the pontoon deck rails use 1.5" to 2" SS steel screws. Mix up a 1/2 pint of CPES in a clean liquid dish soap bottle. For every screw you drive in the plywood, place a 1/2 teaspoon of the CPES on the spot for the screw and drive it just below the top. The screw will pull the CPES into the wood and seal it. Any cuts or holes you put into the deck should be treated w/CPES to prevent water intrusion. There are several CPES mfgrs. Here is one http://www.rotdoctor.com/products/cpes.html

A final step to connect several sheets of plywood together and make the deck one solid piece is to install a layer of 20 oz. fiberglass to the deck using L&L (Laminating & Leveling) Epoxy."