ply wood for deck

[nickoleyt]

Ok, I have read all the posts on re-decking. Here is the question I still have.

If your on a very tight budget, and you plan on selling the toon within a couple years, do you really need to use marine grade ply? can you use treated ply? Can you use treated ply and coat it with something? Do you need to put rubber inbetween aluminum and wood?

Ok a couple question........

Thank you!

[Bamby]

Ok, I have read all the posts on re-decking. Here is the question I still have.

If your on a very tight budget, and you plan on selling the toon within a couple years, do you really need to use marine grade ply? can you use treated ply? Can you use treated ply and coat it with something? Do you need to put rubber inbetween aluminum and wood?

Thank you!

I understand you're concerns about costs, but I've got to play the devils advocate here. Sure you may be only planning on using your boat a few years but a few could stretch to several. Or what about the maybe even poorer less unfortunate person you sell or should I say dump your problem on down the road. Therefore personally I'm unwilling to recommend shortcuts that compromise the long term integrity of really anything.

Anyway I've read and heard a lot of good reports about plywood treated by this http://www.eswoodtreatment.com/ product and it is available in some areas. Supposedly it sells a lot cheaper than rated grade marine plywood though I have no real prices on it. Check it out and see if it is available in your area at an affordable price to you.

[GregF]

A good exterior grade plywood will work as well as marine plywood. The only difference is marine has no voids in the plys like CDX and it is "A" finished on both sides. If you buy "underlayment" rated plywood the knot holes are plugged on the interior plys and if you get 7 ply it is as strong as marine. Just be sure it is exterior glue. No matter what kind of plywood you get, be sure you seal all 6 sides and all the penetrations. It will last for many years.

I used MDO on mine and it is over 20 years old, in salt water. That is 7 ply, exterior glue with an overlay on it. They use it for billboards and sometimes for concrete forms when they want a glass finish.

[RonKMiller]

Western Fir - a VERY soft wood - is junk compared to Meranti, a tropical hardwood commonly used in BS1088 certified marine plywood.

Marine plywood is more stable, has less potential for checking, and the overall strength and stiffness are better than common exterior plywood. For the same thickness marine plywood always has more plys and uses superior quality glues that have to past boiling and immersion tests.

Since the plywood deck is an integral part of the overall strength of a pontoon frame I would never consider using an inferior product.

You get what you pay for - and especially when it comes to plywood.

[GregF]

I have 20 years on my deck and it is still doing fine. How long do you want out of it?

This is not a trailer queen either, I put about 400 hours a year on my boat, salt water, it is never covered and it has carpet on it.

[GregF]

This plywood was installed in the spring of 1989, the picture was taken in July 2010 when I cut out a bad spot around that bolt that was not sealed when I drilled the hole.
The rest of the deck is solid.

[hotairgypsy]

well i am going the cheap as we speak...i got a full 4x8 sheet of treated wood...i am adding some protection with some oil based outdoor paint as per the recommendations of others here. I have applied 5 coats of paint over the past week. This was paint from home depot. it was a can of oops paint..didn't care about the color since it will be under the carpet. I didn't coat all sides. i am going to be installing under-skinning once i am all set. it will bottom protection and some top so we shall see how it does. The first pic is before i started coating and then after.

[GregF]

Be sure you get the paint soaked into the edges and coat all penetrations.
Plywood virtually always fails from the edges, not the surface.
This is a picture of the failed part I took out.
The water started at a drilled hole and wicked it's way along the edge about 2" deep for about 10"
You can see a little damage around the second drilled hole on the left but that was just a small spot.

[FloterBoter]

Since the plywood deck is an integral part of the overall strength of a pontoon frame I would never consider using an inferior product.

lol, that is a ridiculous statement. by the time any plywood is contributing too little to the torsional stiffness
of the assembly (which is all it does), you will have put your foot through it. the bending loads of supporting
weight are much more demanding than the membrane loads of adding torsional stiffness.

[RonKMiller]

I'm much more interested in horizontal shear forces than torsion or modulus of elasticity... commodity plywood with multiple air pockets, concealed knots and tons of bark filler creates numerous opportunities for catastrophic failure.

What's ridiculous is even having this discussion. Regular plywood is garbage.

[GregF]

If spending an extra $400 on marine makes you feel better, go for it.
Just be sure you seal it well or it will fail about as fast as CDX.
Personally I am going with MDO again on my next boat. That overlay is better than an exotic tropical hardwood. It is pretty expensive too, compared to what you find at HD but the OP did say he was only looking for a few years out of the deck. If he sells the boat to someone who will plan on using it for another 20 years it may make a difference. If the boat ends up at a scrap yard, there is no difference at all.

[FloterBoter]

I'm much more interested in horizontal shear forces than torsion or modulus of elasticity... commodity plywood with multiple air pockets, concealed knots and tons of bark filler creates numerous opportunities for catastrophic failure.

What's ridiculous is even having this discussion. Regular plywood is garbage.

oh stop. there are a lot of pontoon boats out there with "regular plywood" decks.
how many catastrophic failures in shear or torsion have you seen? none that you can document.
yes, document, because you're blowing smoke.

a pontoon frame stripped down to just logs, brackets and cross members is still pretty damn strong.
it just flexes more in torsion than some people would expect. adding the flooring adds some stiffness,
but the rails and furniture contribute a lot. the only way using regular plywood would lead to
"catastrophic failure" is if you're running the thing on the ocean during "the perfect storm", and then
you're going to die anyway.

regular plywood won't last as long--the floor will get soft and someone will put their foot through it a lot
earlier than with marine ply. as for your "integral part of the overall strength" and "numerous opportunities
for catastrophic failure", frankly, you don't know what you're talking about. your mention of modulus of
elasticity proves that beyond a doubt. plywood is anisotropic, with three moduli of elasticity due to the
ply layup and wood grain orientation. and the moduli are heavily dependent on moisture content.
so please, just stop.

[GregF]

I also see people talking about PT plywood.
If your boat had PT plywood it is probably garden variety exterior grade BC.
Actually 20 years ago when I was doing my boat the manager of the Wolman plant (one of my customers) said he would treat any plywood I would bring him but he also said I was wasting my money. PT is mostly to stop insect damage and he said the PT process might even cause it to delaminate if he actually shot any meaningful amount of product in it.

[FloterBoter]

This plywood was installed in the spring of 1989, the picture was taken in July 2010 when I cut out a bad spot around that bolt that was not sealed when I drilled the hole.
The rest of the deck is solid.

yup, wouldn't want that nice solid deck after 20 years--might have a catastrophic failure!!
sorry, RonKMiller is just killin me.

[RonKMiller]

Blowing smoke?

I could get into the semantics of engineering terms all day long if you would like, but I prefer to show ACTUAL results.

The attached table shows just how much better Meranti (Hydrocore 1088) is versus Doug Fir -and I stress that the table shows MARINE GRADE FIR which is head and shoulders better than any junky "concrete form" plywood you can buy at your local big box.

Take a good look at the 12mm column (3/4", which is the most commonly used on pontoons) and see for yourself. Meranti absolutely trumps Fir. While bending characteristics are pretty much equal this isn't really a consideration since they are both supported by stringers. Tensile, compressive and shear characteristics are far more important when it comes to defining overall "strength". When you can buy Meranti for almost the same cost as Fir there is no contest.

Oh yeah, Meranti has DOUBLE the screw holding strength - something that is sure to piss you off in a year when you start tripping over them in the middle of the night.

"Once you say you're going to settle for second best, that's what happens to you in life" - John F. Kennedy

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