Re: what differance is there between marine plywood versus treated plywood?
First of all, both marine grade and treated plywood use exterior glue. Neither should delaminate under exposure to water if they are manufactured and graded properly. (Many mills cheat on the grade of treated plywood, and you will find individual sheets that do delaminate)<br /><br />Treated plywood is never a sanded product, and marine grade always is. While treated plywood should be made out of exterior veneers, personal experience says that most plywood is treated after it leaves the plant, by someone else, and a consumer is never quite sure whether all the rules were followed or not. Once a panel leaves a mill, they lose control over how it is used.<br /><br />What you need really depends on what you use it for, and what kind of conditions it is exposed to.<br /><br />If it is only occasionally exposed to water, and allowed to dry, and stays mostly dry, and you want to glue a carpet or something like a carpet to it, all you really need is a good ACX sanded(preferably west coast fir) panel. It is exterior, won't delam under normal circumstances, and will last a long time if kept reasonably dry most of the time. <br />(I can get into the technical reasons why an ACX panel is considered an exterior panel, where an ADX panel is not, even though they both use waterproof glue, if anyone wishes)<br /><br />Treated plywood will be difficult to get anything like a carpet to stick.<br /><br />Marine grade, while an outstanding panel, is usually a fair bit overkill, and is generally only needed if there is serious constant wetting of the panel--and as it is made out of wood--it is not a perfect product and there are lots better, cheaper materials to use these days (like fiberglass or something similar) which of course is why it is less used, and often difficult to find these days.