Why not pressure treated plywood?

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halfmoa

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Why should I not use pressure treated plywood for the deck of my boat? Why go through the expense and labor of epoxying the floor when it's on fresh water maybe once a week for the 4 months of boating (read: not stored in the water and used daily) and the American Wood Protection Association has ratings specifically for marine usage? Is there a concern with chemical reactions between the hull material (aluminium in my application) and deck? Is the reason "because that's how it's done properly"? If so please elaborate because " 'cause someone/I said so" isn't acceptable as there are ratings available for constant moisture exposure. Are there enviromental concerns? Has anyone used pressure treated wood and if so what was the outcome? Posts with "good luck with that" themes need not apply...

For what it's worth my application will be in a 1972 Starcraft Super Sport which will have a new floor applied this winter. And just to brag a little I drilled some test holes in my transom yesterday and it was dry as a matchstick. Yes, I sealed the test holes with 5200.

And thanks for your help and opinions everyone! I'm not new to boating but I'm a new boat owner with a lot to learn about maintainence! This board is INVAULABLE!

halfmoa
 

sje0123

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Re: Why not pressure treated plywood?

Unfortunately I cannot provide much feedback. However, the previous owner of my newly purchased '79 Starcraft SS just screwed some pressure treated wood to the old stuff (Unknown condition to me) and carpeted over it. Since it was done only last season I cannot provide details on its durability. I'm just going to leave it until it gives me trouble.
 

Ciera2450

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Re: Why not pressure treated plywood?

galvanic reaction between the wood and aluminum is the concern I believe.
Can't tell you much more than that, as I have no experience.
 

jigngrub

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Re: Why not pressure treated plywood?

Pressure treated plywood in boat building is very misunderstood by 95% of the people doing work on their boat.

The truth: you can use pressure treated plywood on your aluminum boat BUT!, it has to be kiln dried CCA pressure treated plywood like this:
http://www.pontoonstuff.com/pontoon-boat/144-marine-plywood.asp

The ASQ pressure treated plywood like you buy at Home Depot will eat/corrode your aluminum boat and it also has a very high moisture content that will render flooring adhesives into worthless goop.

Truth: If you do use the CCA PT ply you need to seal the top side of the deck if you're going to install carpet, even though it won't rot you'll still get water damage and cracking. We all know how carpet loves to soak up and hold water. I would still even seal it if you're going to use a vinyl flooring. You don't need to worry about sealing the underside of the plywood unless you're going to install it on a pontoon for obvious reason.

Does this help?
 

halfmoa

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Re: Why not pressure treated plywood?


Not that I don't appreciate your response, because I truly do especially in light of the fact that you responded within minutes of my post, but this thread is an example of "because" rather than scientific statements. i.e. "because it causes corrosion between aluminium oxide and the chemicals in pressure treated wood" is irrelevant and baseless unless backed up by fact. I've been burnt on other forums by "experts" who all agreed with an idea I had that failed miserably because none of us truly knew the answer.

Ciera2450, I'd like to know how you search for things on this site because I have almost zero relevant results using the built in search feature.
 

jigngrub

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Re: Why not pressure treated plywood?

Not that I don't appreciate your response, because I truly do especially in light of the fact that you responded within minutes of my post, but this thread is an example of "because" rather than scientific statements. i.e. "because it causes corrosion between aluminium oxide and the chemicals in pressure treated wood" is irrelevant and baseless unless backed up by fact. I've been burnt on other forums by "experts" who all agreed with an idea I had that failed miserably because none of us truly knew the answer.

Ciera2450, I'd like to know how you search for things on this site because I have almost zero relevant results using the built in search feature.

Only one way to find out for sure halfmoa, install some ASQ plywood on your tinny and see for yourself what happens. Shouldn't take more than a year or two for your boat to become so pitted and corroded that you regret ever touching a piece of ASQ PT.
 

halfmoa

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Re: Why not pressure treated plywood?

The ASQ pressure treated plywood like you buy at Home Depot will eat/corrode your aluminum boat.

Humbly, and with respect jigngrub, why? Based upon what research? Personal experience or forum readings?

Again, I've been burnt HARD by opinions on another forum (it was in regards to an electronics/microprocessor theory and speculation but nevertheless) that weren't based on scientific research and I appreciate the responses!
 

Woodonglass

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Re: Why not pressure treated plywood?

If you would take the time to search this forum, you would find multiple instances of the corrosion caused by pressure treated plywood to aluminum boats. We have some of the most experienced PRO's on the web on this forum and that's why iBoats is #1. You can't compare the responses here with other forums. It is not even close. Here's some facts for you since years of experience don't seem to be enough.

http://www.canada.com/ottawacitizen/news/homes/story.html?id=23a1217b-9527-4ebb-81f1-97cf362d841d
 

109jb

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As stated ASQ PT plywood will cause corrosion unless dried thouroughly and insulated from the aluminum. Example- they used to flash PT decks on houses with aluminum flashing material when all the wood was CCA treated, but now they use galvanized steel because tge ASQ will eat the aluminum flashing. I've seen this with my own eyes. I also had a Starcraft SS that i put a pt floor in. As i said, I dried the wood and insulated it from the aluminum. i dried it by stacking it with 2x2's between each piece and my barn loft for about 2 months. I insulated it by painting bedliner on the aluminum that would be in direct contact and then putting 2" wide pvc tape on the under floor stringers. I then screwed the deck down with SS screws. Since the wood had been dried, ot took carpet glue fine and that boat sat outside all the time for the next 5 years or so ubtil I sold it. Doing it the way I did I never had a problem. That was ASQ pluwood. As stated earlier, CCA plywoid doesn't have the corrosion isdue that ASQ does. You can put CCA plywood right on the bare aluminum.
 

halfmoa

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Re: Why not pressure treated plywood?

This link http://www.google.com/url?sa=t&sour...wsd3AWUsg&sig2=CkZbJseDDEtDgOHbLWXiuA&cad=rja suggests, albeit indirectly, that galvanic corrosion is the problem and a medium between the wood and metal is the solution. That's fine except that the wood must be secured to the aluminium with a metal fastener that will complete the "electric circuit" of galvanic corrosion.

At least we're headed in the right direction...although copper and arscenic are both metals and would, in theory, both lead to galvanic corrosion...and arscenic treated wood is apparently still in production for marine use....:facepalm::confused:

Perhaps this is the reason to coat your untreated deck in a layer of epoxy and hope for the best....no chemistry. I wonder what the manufacturers do/did? Anyone in the production industry care to chip in here?

I promise I'm not trying to play devils advocate here, I just can't afford/stand to do the same job twice!
 

sprintst

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Re: Why not pressure treated plywood?

I went marine plywood on the transom to avoid the voids in the wood aside from the possible galvanic corrosion issues of pressure treated.

It was such a pain to pull up the old deck and deal with the limited hull corrosion I had it was the last thing I would want to deal with again considering I'm keeping the boat for the long haul.

If the preservative has any metallic compound in it then it's out for me. Maybe mythbusters can handle this one to see if the dissimilar metals reaction is due to direct contact or if the corrosion is as noticeable from chemical leaching as well.
 

halfmoa

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Re: Why not pressure treated plywood?

Directly from http://www.yellawood.com/products/acq

Warning-Do not use wood treated with ACQ (Alkaline Copper Quaternary) in direct contact with aluminum.

It's amazing how you can search for something until you're blue in the face and another person can phrase your question in a different manner and find exactly what you've been missing. A manufacturer's recommendation, though lacking specific scientific references, is good enough for me.

Confused to educated in less than an hour! I LOVE THIS FORUM!!!!!!!!! Thank you all!!!!!!!!!!!!!
 

jigngrub

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Re: Why not pressure treated plywood?

This link http://www.google.com/url?sa=t&sour...wsd3AWUsg&sig2=CkZbJseDDEtDgOHbLWXiuA&cad=rja suggests, albeit indirectly, that galvanic corrosion is the problem and a medium between the wood and metal is the solution. That's fine except that the wood must be secured to the aluminium with a metal fastener that will complete the "electric circuit" of galvanic corrosion.

At least we're headed in the right direction...although copper and arscenic are both metals and would, in theory, both lead to galvanic corrosion...and arscenic treated wood is apparently still in production for marine use....:facepalm::confused:

Perhaps this is the reason to coat your untreated deck in a layer of epoxy and hope for the best....no chemistry. I wonder what the manufacturers do/did? Anyone in the production industry care to chip in here?

I promise I'm not trying to play devils advocate here, I just can't afford/stand to do the same job twice!

Call around to the boat dealers in your area nand ask where you can get the CCA ply, it comes with a lifetime warranty.

... and before you go whining about the arsenic and other chemicals in the CCA, every piece of pressure treated lumber you ever came into contact with before 2002 was CCA pressure treated lumber.

Or, you can go with the ASQ PT... I triple dog dare you!
 

halfmoa

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Re: Why not pressure treated plywood?

We have some of the most experienced PRO's on the web

That's what the last forum I trusted said too. Just trying to cover all the bases before I make a move. Thanks for your input.

you do know how to use a search engine, don't you?

Yes, and we've all had the correct answer in front of our faces and refused to believe/understand/accept the truth. That's why I respect the opinions, research, and experience of the members of this forum more than that of my random googlings. (wait...is googlings a word?)

Or, you can go with the ASQ PT... I triple dog dare you!

Maybe mythbusters can handle this one

I'm gonna bolt a section of pressure treated wood to a plate of aluminium in my backyard and leave it for a while. I may even make two and put the second one through a daily saltwater wash down.


Again, I appreciate the responses and this forum is invaluable.
 

Ciera2450

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Re: Why not pressure treated plywood?

this gives a bit more information on the subject of ACQ treated wood and its properties.
View attachment index2.php.pdf


I'm not sure what explanation your looking for.
A chemical reaction(galvanic corrosion) between copper(ACQ) and aluminum is a scientific process:confused:

As for searching on the forum, the broader your search the more results you will get. For example, to find an explanation to help with your post.....I searched ( aluminum plywood )


Someone at one time posted a link to a website that had great prices on CCA plywood. I'll see if i can find it.
 

ondarvr

Supreme Mariner
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11,527
Re: Why not pressure treated plywood?

Or you could read the info that is supplied by Home Depot and the lumber company they bought the wood from. It has all the warnings AND reasons why not to use it with aluminum or unprotected metal, in fact each piece of PT wood has the warning stapled to it.
 

Bamaman1

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Re: Why not pressure treated plywood?

I've never seen so much info on one posting.

After 20 years use, I replaced the back end sheet of plywood on my pontoon boat 5-6 years ago with regular painted plywood. Water blowing in our boathouse door promptly rotted the replacement plywood. The front 5 sheets of OEM marine plywood is as solid as it was when the boat was new.

Marine plywood must be purchased at a specialized wood or plywood supplier, and is available in virtually any major city. It's expensive to order online due to high delivery costs. Sometimes you've got to call around to find it. Lowes/Home Depot doesn't sell such specialized products.
 
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