Pressure treated plywood reaction with aluminum

[Bill Rousseau]

A friend and I are replacing transom plywood and floor in an old 16' Grumman. Transom was two layers of 3/4" with
a layer of 1/2" between them - all with heavy rot. Aluminum on both sides with numerous bolt holes from old homemade gill bracket. I'm pessimistic about keeping new wood dry and am considering pressure treated plywood in spite of the voids
for rot resistance. In one of the threads someone mentioned reaction with aluminum and I was hoping for more info
on this.
Thanks,
Bill Rousseau

 

[Piece715]

Re: Pressure treated plywood reaction with aluminum

There are plenty of threads out there with this type of information. Just do a quick search and you'll find all you need to know. Many informative threads on replacing transoms as well. Proper replacement of a transom will give you many years of proper service. Cut corners it can be a huge safety issue. Search transom replacement and again all the info is there. Good luck and welcome to iboats

 

[jigngrub]

Re: Pressure treated plywood reaction with aluminum

The ASQ pressure treated plywood you would buy at the local big box store or lumber yard will eat/corrode your aluminum alive!

Here's a thread you should read:

http://forums.iboats.com/boat-resto.../why-not-pressure-treated-plywood-514777.html

 

[Woodonglass]

Re: Pressure treated plywood reaction with aluminum

Welcome to iBoats!

PT is a no go for Aluminum boats. If you properly prep a good grade of Ext. Plywood prior to installation, maintain and care for the boat in an appropriate fashion, the new "Wood" transom will last for decades. It's ALL about Maintenance and Care. I'd encase the wood with 2-3 coats of epoxy and then 2-3 coats of Oil Based Rustoleum Paint. Make sure you predrill and coat any penetrations into the wood with Epoxy as well. Do this and you won't ever have to replace it again.

 

[Ned L]

Re: Pressure treated plywood reaction with aluminum

Woodonglass mentioned the best method. However if for some reason you do need to use pressure treated (say if this is a commercial fishing boat & things are just sloppy & get beat up or something similar), I think all you really need is a physical separator between the PT plywood and the aluminum. PT lumber has heavy salts as the preservative. Even a layer of roofing felt wouod keep the wood away from the aluminum. Just be careful to make sure all the areas are protected. (Or am I missing something here??)

 

[jigngrub]

Re: Pressure treated plywood reaction with aluminum

Woodonglass mentioned the best method. However if for some reason you do need to use pressure treated (say if this is a commercial fishing boat & things are just sloppy & get beat up or something similar), I think all you really need is a physical separator between the PT plywood and the aluminum. PT lumber has heavy salts as the preservative. Even a layer of roofing felt wouod keep the wood away from the aluminum. Just be careful to make sure all the areas are protected. (Or am I missing something here??)[/QUOTE]

A little bit.

There is a pressure treated plywood made especially for the marine industry, it is CCA pressure treated plywood and is installed in some of the better built aluminum boats at the factory.

Marine CCA plywood is kiln dried after pressure treating, so it is completely dry when you buy it and will readily absorb protective resins if you desire to apply them.

Most CCA plywood manufacturers have a lifetime warranty against rot for their product.

Now the bad part:

CCA pressure treated is hard to find! About the only places you can find it is at marine dealerships that work on boats, especially pontoon boats... and they may not have any, but will probably know where you can get it.

Kiln dried pressure treated marine plywood is expensive, between $70-$90 a sheet.


HDO or MDO plywood would be a better choice, it's easier to find and cheaper... and is also used in the marine industry because of it's water resistant characteristics.

HDO and MDO are used for making exterior signs, concrete form construction, and boat building.


Coating any plywood you use with epoxy resin will extend the life of it if sealed properly with multiple coats and making sure all penetrations are sealed too.