marine plywood - The Hull Truth

slund · 09-07-2005, 04:55 AM

I was fixing my hot tub cover and decided to put 11/32 between the cover and the insulation for extra ridgitity. Then I decided to seal whith thompsons wood sealer but now I may be a little concerned with the chemicals. It is a moist and hot spot. How does marine plywood differ. How much should a 4/8 by 11/32 cost. What is the best place to get it.

Mud Runner · 09-07-2005, 06:30 AM

Call Woodply Lumber in Freeport.

Garett · 09-07-2005, 06:56 AM

Why do you feel you need extra wood there?

Is what's there decaying? If what's there isn't decaying you don't need extra unless the cover/ top doubles as a dance floor.
But if you feel you need to add just to compliment what's there, then I would only add 3/8" or even 1/4" glued with water proof glue. Watch out for the overall weight if you add to much wood.

slund · 09-07-2005, 08:30 AM

actually there is no wood there it is a pleather cover that has a styrafoam insert for insulation. Unfortunately the styrafoam has crunched up creating a pool of water in the middle of each side of the hot tub. winter covers are much more rigid and I saw an opportunity to slide plywood in there to fix the pooling of water problem..In the winter the snow weighs a lot and I figured this is a lot better than having to pay 400 bucks for a new cover that will only have the same problems. I think 11/32 plywood is slightly thinner than 3/8. .34 verses 0.375

morechaching · 09-07-2005, 08:34 AM

1/4" is plenty thick enough - all you need it for is to retain rigidity until you clean off the snow. I'd eitehr slip in untreated marine, or cover with epoxy all sides

pooldoo73 · 09-07-2005, 10:21 AM

Marine plywood is not treated in any way. If you feel you must add some extra support to the cover, just get a piece of regular old CDX plywood of the proper thickness. Then, buy yourself about a half gallon of epoxy resin. Epoxy resin will be like your Water sealer in this application. You just have to mix 2 parts together. Even if you have never used epoxy before, you can do this without messing it up. When you get the wood cut like you want it, you will simply brush the mixed epoxy onto the plywood. The wood will soak it up somewhat. You can go by West Marine and get a booklet on working with epoxy for about $3. It is very informative. Order the epoxy from uscomposites.com . The main thing you have to do is mix the devil out of the epoxy before applying it and have a clean, dry surface to apply it to. You'll put on about 2 good heavy coats and that piece of wood will last longer than your house.

RI Builder · 09-07-2005, 10:28 AM

Quote:

pooldoo73 - 9/7/2005 10:21 AM

Marine plywood is not treated in any way. If you feel you must add some extra support to the cover, just get a piece of regular old CDX plywood of the proper thickness. Then, buy yourself about a half gallon of epoxy resin. Epoxy resin will be like your Water sealer in this application. You just have to mix 2 parts together. Even if you have never used epoxy before, you can do this without messing it up. When you get the wood cut like you want it, you will simply brush the mixed epoxy onto the plywood. The wood will soak it up somewhat. You can go by West Marine and get a booklet on working with epoxy for about $3. It is very informative. Order the epoxy from uscomposites.com . The main thing you have to do is mix the devil out of the epoxy before applying it and have a clean, dry surface to apply it to. You'll put on about 2 good heavy coats and that piece of wood will last longer than your house.

Exactly - the only difference I would offer is go to system threes website and you can download the epoxy book for free. They also offer a free trial kit - which may be enough to complete your project.

Afishinado · 09-07-2005, 10:55 AM

What about 2 pieces of underlayment (3/16" about) and sandwich 2" rigid foam between and glue? Cheap, strong, and water won't hurt it.

jb_dallas · 09-07-2005, 04:42 PM

I just replaced the stringers on my ski boat with marine grade plywood. The guy at the wood store told me that the only difference between regular plywood and marine grade are the veneers. Marine grade plywood doesnt have any patches in the veneers, which allow water to penetrate the board. Marine grade board also has a larger number of veneers for strength. There is no special glue or coating on marine plywood, it is based on the construction of the board.

JB

tobnpr · 09-07-2005, 07:26 PM

Plywood (marine or CDX) and epoxy is too much work and expense for what you're trying to accomplish. Get a sheet of pressure-treated plywood, cut it to size and be done with it

Blue C's · 09-08-2005, 06:37 AM

Even if you use a sheet of plywood, when heavy snow sits on the cover with the plywood in it, the high moisture content will allow or cause the plywood to form and keep the "bowl" shape again. Even with Marine plywood. Even if it causes only a 1/2" dip in the cover, it will allow water to "birdbath" on the cover.

If this is the case, you could actually remove the plywood every other week or so and turn it over so the dish shape is now a dome shape.

If not and the thickness of plywood isn't strong enough to support the weight of the snow or whatever else is bearing down on it, then you're wasting your time.

jobowker · 09-08-2005, 03:41 PM

There are differences between marine and other plywood. All plywood rated for exterior use has waterproof glue. The big benefit of marine ply is that there are no voids (theoretically) and generally more plies (5 vs 3). It can still have patches in the veneers in in the inside layers - they use teh patches inside to eliminate voids. In either case, you can epoxy the crap out of it and it won't rot unless you breach the epoxy barrier, like nailing, screwing, or drilling into it.

I would almost try getting away with plain old pressure treated wood, except that it will be hot and wet 24/7.