aluminum vs. treated wood

I have an aluminum canoe that I stored under my deck for winter. I took it out today to use it and I noticed that the aluminum is pitted in one area. I believe that I had the ends of some treated wood blocks up against this part of the canoe. Could this cause the pitting? I also had some aluminum clad house windows in which aluminum corroded. The dealer told me that the pine resin from the wood under the aluminum caused the damage. I am considering putting a flooring in my 14 foot aluminum boat and I need a wood material that will not react in this manner. What is the cuprit, pine resin or treated wood? What type of wood do I need to use for flooring? What exactly is marine grade plywood? Do building centers carry this? Thanks.

Re: aluminum vs. treated wood

The pitting is caused by some of the chemicals used in the pressure treating process. That is one reason bunks on a trailer are never pressure treated wood. As for doing a project on your aluminum boat, I would suggest using marine grade plywood. I used some 3/4" to pulled a bow deck on my boat and covered it with epoxy resin. It's messy to work with but extremely durable and weather resistant.

Re: aluminum vs. treated wood

While I can't say anything either way about pine resin for lack of knowledge on the subject, the pressure treated wood is definitely the culprit in the canoe's case. You see, modern pressure treated wood is copper impregnated, due to government regulations. Copper and Aluminum are dissimilar metals, and thus will react with one another. Yours is not the first confirmed case of this, and I see it quite regularly. Lowe aluminum boats have recently been having a little trouble with that issue (as in replacing boats under warranty), as they still use pressure treated wood in the transom. While it takes years for that to corrode through in a freshwater environment, the folks that use those boats in salt are finding holes in the transom.

For the deck on your tinny, I have, and would again, go with a standard plywood from Home Improvement stores. I have used marine grade in the past, but I couldn't see enough improvement to justify the extra cost (100 bucks a sheet). I would advise going with the next grade up from the outdoor sheathing (can't remember the name), as it usually has one more ply, and has fewer voids, as well as a better quality finish on the outer layers. Do coat the lumber with a water sealer, either spar varnish, Thompsons, or at the very least a good oil based paint. My first choice, however, I would go with aluminum, as it is the wonder material - won't rust, bust, or collect dust, but that is just me, seeing as I am an alumaholic.

Re: aluminum vs. treated wood

Yes, the chemicals in PT wood will eat aluminum (slowly). Best to use non-pt wood and seal it for boat projects

Re: aluminum vs. treated wood

When I decked my jon boat, I used a different type of plywood...

I had worked at a cabinet place for a while, and they have there, something called "verola" its a 3/4" cabinet grade 8-ply plywood ... extremely strong because of the 8-plys (wont find that in any regular 3/4" from home depot, its all 3 or 4 plys).. and its already finished for smoothness on the faces... you can basically paint it, stain it, seal it, or fiberglass it as you see fit, and it comes out beautifully because its so smooth to start with...

runs about 35 bucks a sheet (@cost)... may have to give them a little something extra...

For doing marine repairs, I find it to be the most reliable, best finish, and sturdy plywood available... and I agree, as long as you seal it, it doesnt matter... Marine ply is extremely expensive, and not worth the cost if you're going to seal the wood anyway... just my opinion.

Just find a local cabinet shop and I am sure they would be willing to sell you what you need... like I said you may have to give them more than cost though (like 10bucks/sheet more?)... i knew the owner at the one i used to work at so he gave it to me for cost

Re: aluminum vs. treated wood

I'm sure the conditions were ripe for this to happen with snow dripping off the deck and wetting the wood stored below, which likely sped up the process. I did briefly treat my deck with a desk wash this spring. This stuff is largely bleach, however, and the spot in question I'm almost positive is where the treated lumber was resting up against it. Bleach should be safe, correct? Will a galvanized steel chain also cause the same type of reaction with aluminum? I have been using one to lock my canoe up. By the way, the lumbar in question is the CCA stuff. Thanks for the feedback. I'm sure a lot of folks are not aware of the problem. I'll keep my Grumman clear of this stuff in the future.