Marine grade question

[geedubcpa]

How long should marine grade plywood last if it has constant exposure to water?

 

[Greg Mrozinski]

Re: Marine grade question

How exposed? In the the rain? Totally submerged?

Marine ply is not that much more water resistant than normal exterior plywood. Big advantange with marine ply is the number, quality and uniformity of the plys (non or little-voids). This leads to a big difference in strength. Any plywood that is not protected and exposed to water constantly will rot in time.

 

[ondarvr]

Re: Marine grade question

Plus, there are so many different types of wood used to make "marine plywood" that there is no one answer to the question. Some of the wood used is much more rot resistant than others, some are flexible, some are stiff, so what gets used is determined by the needs of the application.

 

[ezmobee]

Re: Marine grade question

The important thing to note is that contrary to popular belief, marine ply is NOT treated. It's just what Greg explained it is above and nothing more.

 

[geedubcpa]

Re: Marine grade question

For a floor replacement on a aluminum boat is it worth the extra to go marine grade - or is the exterior grade going to give me the same durability - I would epoxy or fiberglass resin either type. I have two pieces that are 48 inches by 60 inches needing replaced.

 

[ezmobee]

Re: Marine grade question

No the exterior grade is not going to give you same durability. Marine grade is a superior product. Is it worth it? Only you can decide.

 

[geedubcpa]

Re: Marine grade question

What about the coating - fiberglass resin or epoxy?

 

[ezmobee]

Re: Marine grade question

You cannot coat with just fiberglass (polyester) resin and no glass. It does not have the same adhesion and strength as epoxy and will crack. Epoxy you can use by itself.

 

[Mark42]

Re: Marine grade question

Three words: Pressure Treated.

 

[ezmobee]

Re: Marine grade question

Aluminum boat Mark......

 

[geedubcpa]

Re: Marine grade question

Yes I started going down the treated lumber route then read what can happen - does anyone know if this really does happen? At any rate I have switched over to marine grade to be safe.

Do you apply resin to both sides of the plywood? I think so but wanted to make sure.

 

[fishrdan]

Re: Marine grade question

Yes I started going down the treated lumber route then read what can happen - does anyone know if this really does happen?

Yes, the chemicals for the new style pressure treated wood will eat aluminum. My 07 Tracker jon boat had pressure treated marine plywood on the transom, the new green treating not the old style orange/yellow "marine" treating. I replaced the transom plywood (went bigger) and noticed that the pressure treated plywood Tracker used was beginning to eat the raw aluminum, lots of corrosion,,, in 2 years!

What thickness of deck plywood are you installing? I have used 1/2" 5 ply exterior plywood and it's one heck of a lot stronger than regular (3 ply?) 1/2" exterior plywood,,, but still about half the price of marine plywood.

I used marine plywood in my Crestliner rebuild,,, $600 for 8 sheets of 3/4 One of the big differences I noticed with douglas fir marine plywood I used is that the plies are laid at 45*, not at 90* like most other plywoods. One disappointment was all of the plys are supposed to be void free, the knots removed and boat patched so the plywood is void free. Well, it wasn't void free as I had a couple screws blow through on the deck. Kind of frustrating since I spent $75/sheet for the stuff...

 

[geedubcpa]

Re: Marine grade question

I am using 3/4 inch marine grade - I was at 1/2 inch but I want to install some pedastel chairs and thought I needed the extra strength - the added weigh isnt that big a deal because its only 1.5 sheets.

3/4 weighs about 25lbs more than 1/2.

 

[ghamby]

Re: Marine grade question

Three words: Pressure Treated.

Three words?

 

[Mark42]

Re: Marine grade question

Three words?

Ok so it wasn't one of my better posts....


Regarding the P/T wood, it didn't register in my head that this is an aluminum boat. Sorry.

How about those PVC sheets? Anyone been having success with them as decking?

 

[geedubcpa]

Re: Marine grade question

If they hadnt changed the formula for Pressure Treated lumber then it would be the best and most economical choice for a fishing boat like mine.

 

[Mark42]

Re: Marine grade question

If they hadnt changed the formula for Pressure Treated lumber then it would be the best and most economical choice for a fishing boat like mine.

Might be worth wrapping the edges of the wood in a layer or two of glass mat to protect the aluminum from the wood. Then one layer of mat on the top to help seal and make a nice surface. Even holes drilled for screws can have sealer pumped in from a caulk gun when the screws are run. The chemicals do not leach out like soap from a sponge.

Just an idea.

 

[fishrdan]

Re: Marine grade question

If they hadnt changed the formula for Pressure Treated lumber then it would be the best and most economical choice for a fishing boat like mine.

Yes, "old style" CCA treated plywood is what a lot of aluminum boat manufacturers use, the A stands for arsenic. They can get it, but it's not readily available to the public, and shipping is crazy expensive. ACQ treated is the green stuff and will corrode aluminum.

Like Mark said, (and from what I've heard) you can barrier coat the ACQ treated ply so it has no contact with the aluminum,,, and get away with using it. But I wouldn't chance it rotting out my boat. The barrier can be; paint, rubber strips, thick plastic tape, etc, just something to keep the treated plywood from touching the aluminum. If you do use ACQ treated ply you have to use stainless steel fasteners.