Re: Marine plywood
here are the facts...
1) Marine Plywood and exterior grade plywood use the same exact glue to hold it together.
2) Marine plywood has little to no voids in any of its layers. Exterior plywood may have significant voids within layers.
3) Some marine plywoods may be made with certain woods that are more tolerant to moisture (eg fir) but exterior plywood can also be purchased in many of the same species of wood.
4) Marine plywood typicaly has two "A" surfaces (sanded and no knots). Your most common exterior ply is CDX, C="C" grade face on one side, D="D" grade face on the other and X=indicates that it is made with exterior grade glue.
5) Marine plywood is made with more layers than typical exterior ply.
6) Neither marine grade or exterior plywood is treated with any chemicals.
7) Pressure treated plywood is available but will react with aluminum.
6) There is no difference between marine and exterior ply as far as resistence to rot. The only difference is in the strength, marine ply is stronger due to the higher number of thin plys and the absence of voids.
To be honest I know nothing about pontoon boats but I would make an educated guess and say that most manufacturers would use just plain old marine ply without sealing it with any resin or fiberglass.
The only reason marine ply would last longer than CDX without being sealed is that marine ply is more structurely sound than CDX. It will take less rot to impair the structural integrity of CDX than it will to impair marine ply.
In order of likely longevity of repairs I would rate them as follows (the first being the shortest lifespan)...
1) Untreated CDX or similar exterior ply.
2) Untreated marine ply
3) CDX sealed with several coats of a thinned epoxy resin.
4) Marine Ply sealed with several coats of thinned epoxy resin.
I didn't include adding layers of fiberglass because thats just another layer of complication and I would presume not typicaly done on pontoons (maybe I'm wrong there, don't know).
None of these methods are wrong, but some will last longer than others its up to you to decide between cost and longevity. The delamination during carpet removal is something that ill let someone else discuss. Only thing I'll say is that I believe if the wood was epoxy coated delamination would not be as much of an issue.
{(P.S. I have heard of plywood that is treated to prevent rot (I am not refering to typical pressure treated, marine or exterior grade) and is safe for aluminum. May be available from one of those pontoon suppliers? Don't know much about those. I just chose to focus on the differences between marine and exterior ply.)} - Edit - I was thinking of plydek xl but it seems that is in fact pressure treated and does require a barrier between it and the aluminum. Sorry for the misinformation.
