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Message: <blockquote data-quote="jethro" data-source="post: 509997" data-attributes="member: 12381">Marine grade is intended for glassing. The only difference in marine grade plywood is the spec calls for less than 10% void space within the sheet. Where this is important is when you are making a substrate for fiberglass and completely encasing the assembly with resin. The more voids there are in the plywood, the more expansion and contraction of the substrate is possible due to changes in temperature which could cause cracks to develop. More air can also make the resin bubble while curing. Marine grade plywood is not treated with any product to prevent degradation from water contact. The plys are assembled with waterproof glue just like exterior grade CDX and most other grades of plywood. Even the very best of the best aluminum boat manufacturers (which includes Lund) use exterior grade CDX as substrates for their floor. If you want something that will last 30 or 40 years without issue, cut your pieces to size and then encapsulate with polyurethane on all 6 sides prior to installation. You can vinyl in 96" wide but it becomes way more expensive, especially the shipping. I get my marine flooring from Defender Marine.com but if you want a seamless floor look up PontoonStuff.com. They sell 96" wide in rolls as long as you want.</blockquote>