# pressure treated wood and aluminum



## tripleup05 (Oct 11, 2010)

So in my few days of lurking around here, I have seen alot of warnings against using pressure treated wood on an aluminum hull. However, looking through the mods pages, it seems lots and lots of people use wood. So how are they doing it? I know the most obvious answer is to use aluminum, but it's not really an option due to the expense. There aren't any scrap yards nearby, and new aluminum is _outrageous!_


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## Jim (Oct 11, 2010)

regular plywood and coat it yourself with some poly!

and :WELCOME: Thanks for joining!


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## tripleup05 (Oct 11, 2010)

*humbly* What do you mean by poly? Polyurethane, like for hardwood flooring?


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## Brine (Oct 11, 2010)

IMO, poly's aren't the best option. Once they cure, they become very hard, and once flexed (as in a deck you walk around on) are prone to cracking/failing. Naturally, how you support your decks would also be a factor. 

I think the latest consensus as the "best" sealer is a spar urethane. Not to say you can't just buy a quality deck sealer and have good results too. Many folks on here have. If you know you will be fishing often in the rain, the boat is kept outside etc.... I'd probably get the best sealer I could afford. 

If you haven't looked yet, there are a few guys on here that have gotten some old road signs (legally of course) for cheap. Maybe a phone call to your local DOT is a good start.

I'm using an ACM panel in my build, which I hope ends up being a good middle ground between wood and aluminum. Too early to give dependable review though. The ACM I am buying is $2/sq ft.


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## cavman138 (Oct 11, 2010)

I used marine grade plywood coated with spar varnish.


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## RiverRunner (Oct 12, 2010)

Jim said:


> regular plywood and coat it yourself with some poly!
> 
> and :WELCOME: Thanks for joining!



Same here.....


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## perchin (Oct 12, 2010)

I would have to agree with Brine..... Without batting an eye....... Spar Urathane is the best option, short of fiberglassing a board.

Oh yeah.... It may now-a-days be called Spar Varnish too..... there is no governing on this anymore, so they can call it whatever they want now. Just make sure it is "Spar"... :wink: and :WELCOME:


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## Hanr3 (Oct 12, 2010)

I used regualr plywood, luan plywood, and knotty pine lumber then covered it with oil based outdoor paint and outdoor rated varnish/polyurathane. Both paint and stain/poly are designed to move with the wood, plus it protects the wood from teh elements. A good protectant will last a long time exposed to the elements day and night. 

I did stain and varnish the center box I made for my boat. Teh box contains my cooler (livewell), batteries, front seat, electrical panel. I used Min-Wax varnish and polyurethane. The poly is rated for outdoor use. The box looks as good as the day I built it, 1 1/2 years later. Pics to my build is in my signature.


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## playall8 (Oct 13, 2010)

I found a road construction crew that had alot of old road signs. They had switched to the tarp style fold up signs and had piles of 4x4 aluminum. The guy was real nice and gave me 3 sheets after talking with him.


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## dixie_boysles (Oct 13, 2010)

I just used Fiberglass resin, it works great!!!!!!! $11 a can at Walmart and a 2 dollar roller:







Put on two coats and the wood is good to go! It even says on the back of the can that it can be used as a sealer in light coats (which i did). and it doesn't crack up.

here are my side pieces coated in two coats of the stuff:






and here is my build:

https://www.tinboats.net/forum/viewtopic.php?f=21&t=12178

All of my flooring is wood with the exception of the main floor which is an aluminum roadsign


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## dan h (Oct 14, 2010)

i used regular exterior plywood and a spray can of thompsons water seal 5 bucks at wal mart.lol.


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## Howard (Oct 14, 2010)

Needs to be asked. Which is better, spar or the resin???? And why. Not a fan of Thompson at all, over rated IMHO


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## tripleup05 (Nov 14, 2010)

Howard said:


> Needs to be asked. Which is better, spar or the resin???? And why. Not a fan of Thompson at all, over rated IMHO



+1. I'd like to seem some pro's and con's of each. In my case, price might be the deciding factor. I plan on doing the floor, a rear deck, front storage, and hopefully some side storage compartments and some sort of livewell. Dixie's $11 can of fiberglass resin doesn't sound too expensive, but if it takes six or seven cans that will be a bit pricey! Any idea on the coverage rate of the resin vs. spar urethane/varnish?


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## jcb (Nov 14, 2010)

I use treeted 3/4 ply for me deck extention with no rebuetes and it ben there for two year so far.The treeted ply has gottin very dry and i see no problimbs with it on there.I look and check iot out once i joins up here and reed such rightings.Maybee some has had troubles but i not as of yet and i not going to change it till i see something happening :| live and lurn is all that can be done in life.Make sure yous atleest lurn something everyday thats all that can be expected :wink:


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## msumoose (Nov 14, 2010)

As a wood scientist by trade and education, here is my professional opinion....

Thompson's is a waste of money...all it is is a wax emulsion that will last a few weeks. The wax will 'float' off sooner or later. It ony sits on top of the wood, with little adhesion.

Next best is a oil based paint or stain or poly. This group includes paints, stains, varnishes, urethanes etc. This does not seal the wood totally, but does a MUCH better job than Thompson's. Has some adhesion but, again, it sits on top of the wood.

A better alternative that the oil based is a vinylester resin used for fiberglass. This will penetrate the wood and encapsulate as well. Three coats is gonna last a LONG time. Make sure to do all edges, sides and penetrations (SCREW HOLES). Basically anywhere water could possibly get. There are many, many million dollar sportfishing boats that use this philosophy that are DECADES old with no rot.

The best sealant IMHO is an epoxy fiberglass resin, used the same way. A little upgrade in technology and durability as well.

Another thing to consider is that using the oil based systems, any carpet put down over them is adhering to the finish and not the wood. Concievably, one mav be able to pull up the carpet and have finish clinging to it instead of the wood. Not a good situation.

Just my $0.02


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## perchin (Nov 15, 2010)

msumoose said:


> As a wood scientist by trade and education, here is my professional opinion....
> 
> A better alternative that the oil based is a vinylester resin used for fiberglass. This will penetrate the wood and encapsulate as well. Three coats is gonna last a LONG time. Make sure to do all edges, sides and penetrations (SCREW HOLES). Basically anywhere water could possibly get. There are many, many million dollar sportfishing boats that use this philosophy that are DECADES old with no rot.



I agree... but would also add that resin alone is not uv-friendly, and will (if not covered by paint or carpet) break-down. Where as spar-urathane is supposed to be uv-resistant.

BTW :WELCOME: aboard!!! you'll be a nice addition to this great site for us woodworker's :wink:


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## Hanr3 (Nov 15, 2010)

Not a fan of 100% sealing wood. It must breath or it will rot from the inside out.


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## msumoose (Nov 16, 2010)

'wood will rot from the inside out'....

Nope. If you seal plywood, it is dried to about 5% moisture content after pressing. That water is referred to as 'bound' water, meaning that it is within the cells of the wood. Even pine lumber, which is usually dried to 15% or 19% (the grade stamp will tell you...KD19 means 19%) is in the realm of bound water as well. When you get to 30% or more, then you get to 'free' water, or water that is loose in the staw-like fiber that makes up wood. That is what rots wood, it breeds fungus and allows the fungus and microbes to feed on the wood.

If you seal the wood and it never comes to 30% or so MC, no rot can occur. If you wet the wood and immediately dry it, no problem. If water sits on wood and cannot dry quickly (read: under carpet or vinyl, or under water) then rot begins.

If it never gets wet, then no rot will occur. There are 2000 year old wooden chairs found in the pyramids...


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## msumoose (Nov 16, 2010)

Oh...and Perchin...

I think that there is a West System epoxy that is UV stabilized, and clear so you can use it like varnish, and it will last three to five years in the weather. I saw it while watching Ship Shape TV, he was decking the floor of Alumacraft. Good show, but dont believe the BS about the marine plywood.


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## perchin (Nov 16, 2010)

msumoose said:


> Oh...and Perchin...
> 
> I think that there is a West System epoxy that is UV stabilized, and clear so you can use it like varnish, and it will last three to five years in the weather. I saw it while watching Ship Shape TV, he was decking the floor of Alumacraft. Good show, but dont believe the BS about the marine plywood.



I'm not familiar with that product, but I'm sure it might exist seeing there is a need for it. As far as the marine ply goes, I didn't watch the show, so I don't know what was said about it.


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## perchin (Nov 16, 2010)

msumoose said:


> 'wood will rot from the inside out'....
> 
> Nope. If you seal plywood, it is dried to about 5% moisture content after pressing. That water is referred to as 'bound' water, meaning that it is within the cells of the wood. Even pine lumber, which is usually dried to 15% or 19% (the grade stamp will tell you...KD19 means 19%) is in the realm of bound water as well. When you get to 30% or more, then you get to 'free' water, or water that is loose in the staw-like fiber that makes up wood. That is what rots wood, it breeds fungus and allows the fungus and microbes to feed on the wood.
> 
> ...


Agreed... Boat manufacturers encapsulate wood everyday. If it didn't work they wouldn't continue this method for the last 60 years.

On a side note, I don't start milling my rough sawn until its moisture content is reading 8%.


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## Howard (Nov 17, 2010)

MSUMOOSE: This is great information and all makes sense to me. I have seen allot of wood rot very quickly simply do to poor protection. I have also seen wood last to the elements outside for my life time with proper protection. Is it true when trees are cut at a young age that the wood is more vulnerable for decay?


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## msumoose (Nov 18, 2010)

'Does young wood rot easier than old wood?'

Well, yes and no...and it depends. LOL

Back in the day, all wood that was harvested was old growth (meaning non-plantation) and some say it had more rot resistance than a younger tree of the same species. Hard to prove since there is not much, if any being cut. Nowadays, virtually all pine lumber comes from plantations, and most doug fir, spruce, and larch too. Being in the South, I know most all pine is harvested at about 30 years old, with most earlier thinnings going to chips or pulp. It is hard to get anything other than 30 year old lumber.

So to answer your question...maybe, but all wood is succecptable, just at different rates.


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## HOUSE (Jan 9, 2011)

man...this was a great thread to read, thanks guys.
I bought pressure treated plywood to make my flooring because it was going to sit on top of untreated 2x4 crossbeams sitting on my boat floor. Do you think I'll be safe if I just coat the non-pressure treated 2x4's with that Spar Urathane and then cover the floor with carpet? The PT floor shouldn't have any direct contact with the aluminum of my boat. Does the corrosive stuff leak out of the PT wood and still get onto the rest of my boat?

Thanks...


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