PT Wood on Aluminum

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stalker14

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Okay, here we go again, I am sure some of you are saying. Anyway, I am repairing my aluminum jon boat because PT plywood was used by the manufacturer in the transom and it is causing a significant amount of corrosion. I think I have caught it before it was too far gone. What I want to know is if I epoxy coat and seal the PT wood will that help prevent the transfer of the cooper ions in the PT wood to the aluminum and prevent the corrosion process?? (Or aluminum Ions to the copper whichever it is I don't care for the politically correct chemists out there). The moderator has already said it won't work so I am assuming he has tried this or read about someone that has? Has anyone else tried this with any success??

Thanks for the help.
 
ezmobee

ezmobee

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Re: PT Wood on Aluminum

Why would you want to continue to use PT?

If, for some reason, you are dead set on using a treated product, seek out some true marine PT which I believe is still treated the old way with Arsenic which should not be corrosive. How old is your boat? If it's older than about 7-8 years, then it probably wasn't the PT that did the damage but more likely trapped moisture.
 
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stalker14

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Re: PT Wood on Aluminum

I am pretty sure all PT has copper in it, old and new. That is what kills or prevents fungus. There may be other types of treatment out there but copper is the most common and I am not familiar with the others. A name brand or some guidance would be appreciated on that.

Anyway, the reason for using PT is so that it will last forever, untreated wood will rot eventually, water always finds a way in. Besides the wood I have is already cut to fit and is in perfectly good condition, it is PT you know.
 
jasoutside

jasoutside

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Re: PT Wood on Aluminum

ezmobee said:
Why would you want to continue to use PT?
Click to expand...

That's what I'm wondering too?

Exterior grade, Arauco or Marine grade ply, properly sealed would probably last forever (well a really long time anyway).

:)
 
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stalker14

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Re: PT Wood on Aluminum

Thanks ezmobee that is what I am looking for. Everyone says use marine grade plywood but marine grade is not necessarily treated it is simply ?A grade? throughout and uses an exterior glue, if not sealed completely it will rot just like any old wood, depending on the wood used to make it.

The problem with the treatment is that it usually contains copper which, this stuff does too but it is a type of copper that won?t react with aluminum according to the manufacturer. This is what I need.

I was just hoping I could take a short cut and use what I already have and I was hoping someone out there could tell me that they have sealed regular old PT wood with epoxy and it worked fine, but alas, that does not seem to be the case. I suppose I could be the guinea pig and try it myself but I don?t want to redo this thing again.

Again, thanks.
 
Woodonglass

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Re: PT Wood on Aluminum

Uhmm you said it yourself, "water always finds a way in". If it does and you have Copper Treated Plywood then it will leach out onto the hull and eat your boat. Heck if water never got in, you could use any wood you wanted. If you're gunna use any treated plywood that contains copper you run the risk of damaging your boat. And I can show you some Rotten PT plywood if you would like. Having been in the construction business for 30 years in the past, I have seen it. Takes longer but it will delaminate, lose it's properties and rot. The NEW pontoon ply is something else and I have no experience with it. Supposed to be Great Stuff. JignGrub, a forum member, swears by it.
 
ezmobee

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Re: PT Wood on Aluminum

stalker14 said:
Thanks ezmobee that is what I am looking for. Everyone says use marine grade plywood but marine grade is not necessarily treated it is simply “A grade” throughout and uses an exterior glue, if not sealed completely it will rot just like any old wood, depending on the wood used to make it.
Click to expand...

This is absolutely correct.

The reality is, if your current PT wood is very dry, you could epoxy it, and add a layer of fiberglass. I think that would make the chance of corrosion contact pretty minimal.
 
kfa4303

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Re: PT Wood on Aluminum

Why bother with trying to make PT work, even if you could? Just seal some good quality exterior grade plywood and be done with it. No wood "lasts forever", PT or not. If/when there should be any water intrusion, you certainly don't want any dissimilar metals (copper and aluminum) to come into contact with each other. You've already seen what electrolysis can do to your hull. Why risk further damage? Plus, sealing a new transom with epoxy should leave you with a little extra epoxy, which is handy for all kinds of stuff and you don't have to fiddle with any fiberglass. Just my 2 pennies :/
 
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stalker14

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Re: PT Wood on Aluminum

Correct PT will rot under the right conditions however, a small nail hole or even some crack in the paint will lead to untreated wood rotting out, the fungus starts growing and it is more than just a little bad spot it is a total failure. I have been there and done that. That is why I like the treated stuff, small blemishes in the seal won’t have a catastrophic affect. I do realize nothing lasts forever by the way.

I am still trying to understand why the copper in that stuff does not affect aluminum and the copper in regular old PT does. Any chemists out there? This is something I am curious about and will need to do a little more research on in order to find out.
 
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stalker14

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Re: PT Wood on Aluminum

Thanks WOG for looking that up for me, I saw those and they seem to contradict each other don't they. That is why I am still a little apprehensive about using the pontoon stuff. Obviously we are comparing construction grade lumber to marine decking and there really is a world of difference.

It appears as though the copper is bonded to the chromate in the marine treated plywood and is not available as a free ion to react with the aluminum. The copper is stable. Although CCA treatment seems to be thrown around all over the place there appears to be many variations to it. The marine treated wood is chemically stabilized somehow.

This is kind of why I was wondering if I sealed my regular PT wood with epoxy if it would have a similar affect. I was planning on pre-drilling bolt holes and such so that all areas would be sealed and not drilling after the wood is installed to prevent water from penetrating the wood. Whether I use the pontoon stuff or not I intend to epoxy coat and then imbed the wood into a glue of some sort to the transom, as a barrier to prevent water from being trapped between the wood and the aluminum.
 
Woodonglass

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Re: PT Wood on Aluminum

This ^^^ is true, but again as you said, when you do get a leak, it will leach out and eat your boat. A normal unerlayment 3/4" plywood, epoxied and maintained properly by predrilling and coating all fasteners with epoxy, will last 10-20 yrs. I doubt you'll own the boat that long and if you do. Have your Grandson help you replace it.
 
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stalker14

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Re: PT Wood on Aluminum

Well I have already had the boat for over 10 years and I see no reason to get rid of it especially if I make it better than new. Unfortunately maintenance is exactly what I am trying to avoid, that is kinda the whole reasoning behind treated lumber, of course if it is just going to cause other problems then it is not much of a fix.

I am really not getting my question answered and that is has PT sealed in epoxy ever been used before, I realize I can guess that it wont but truthfully there is really only one way to find out and I understand the risks. It could be great or I could end up right back where I am now which isn’t all that bad if I don’t let it go too long.

I have gotten more help on this forum than any others though, most just say use exterior ply and replace it every 5 – 10 years. Not what I want to do. Thanks for all your help and suggestions.
 
jasoutside

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Re: PT Wood on Aluminum

stalker14 said:
I am really not getting my question answered and that is has PT sealed in epoxy ever been used before
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Well, to answer your question...

I believe I have seen one of the alum boats built with PT and the fella sealed it up with porch and floor paint. Course we won't no the results for years down the road and he comes back here to tell us anyway.

Now, glass boat guys, idunno.

stalker14 said:
most just say use exterior ply and replace it every 5 – 10 years. Not what I want to do. Thanks for all your help and suggestions.
Click to expand...

Personally, I believe this is a VERY conservative ^^^ time estimate. Both of my rigs had unsealed (paint on one side actually) transoms and lasted 35 plus years, many of which were total neglect. The transoms I have put back in my boats I fully expect to last the rest of my days.

Now if you go PT, all sealed up with epoxy (or poly and glass) will you have a problem? Nah, I don't think so. It's your rig do as ya please. And, if you sleep better at night, that's cool.

Have a good one!:)
 
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stalker14

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Re: PT Wood on Aluminum

Right I know the PT will last what I want to know is if I seal it will it be enough to prevent it from corroding the aluminum. I think if I use the treated marine ply I will be okay, they say it won't corrode Al but, I am wary since most of these guys are on lakes and salt water is another story.
 
ondarvr

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Re: PT Wood on Aluminum

I don't think you said how you knew the original wood is PT, if it?s because there is pitting behind it, the pitting doesn't prove anything, aluminum boats used in salt water suffer from this all the time, PT or no PT. I use Marine PT on my aluminum jet boat, it?s been there for ten years with no corrosion issues, but I don't use this boat in salt water, I have a glass boat for the salt.

Epoxy will protect the aluminum from the PT, but the salt water being trapped between the coated ply and aluminum can still cause pitting. Coating the aluminum will help prevent it, at least for a while.

A good exterior grade, or marine ply will last decades in this type of application with no coating. Do you need it to last longer than that?
 
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stalker14

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Re: PT Wood on Aluminum

You are right I am not really sure if the wood I removed from the transom is PT. I think it is, it is in perfect condition. It really doesn't have much of a green color to it. But, I can't imagine wood without any treatment not having any rot in it after 10 years. I also understand about water being trapped and causing corrosion that way. I live in FL and wood rots very quickly if it is not treated, heck even PT will rot under the right conditions. Humidity, heat and fungus is our state flower.

This is why I am thinking of just going ahead and sealing up the wood I removed and cleaning up the aluminum and then basically glueing the wood back onto the transom so it will be sealed to prevent water from getting trapped. The wood is covered on all sides with aluminum and is protected from the elements to an extent.
 
ezmobee

ezmobee

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Re: PT Wood on Aluminum

A couple of starcraft guys have hit the inside of the transom with POR15 or something like that to reduce the chance of future corrosion.
 
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