A plywood observation

[bonz_d]

For whatever it's worth I thought I would pass this along.

As some of you know I've started working on my Alumacraft Classic and have pulled all the plywood out of it to redo it and this is what I've found.. The wood was replaced before I'd gotten this boat and the PO didn't do a very good job of it, which is why it's coming out. How long that stuff had been in there I have no idea but I have owned this boat for 2.5 years now. So last summer knowing that I was going to rip it all out I abused it to see what would happen. Actually left it out uncovered all summer as sort of a test.

I have no idea of what kind of ply this other than it's 5/8th 4 ply. I also looks as if it was painted with brown porch paint and only on one side. The underside was untreated, nothing on it at all. The top exposed side the veneer has a lot of checking in it while the underside doesn't. Every pc. I pulled up is still dry and solid. No signs of delamination, rot or soft spots. I have to say I was truly amazed! I even cut a couple of pcs. to inspect it and the wood was still clean and solid after all this time. I even took one pc. that I'm going to salvage to cut up for a small pc. to replace the missing Bow deck on the Sea Nymph I just picked up.

So before any arguments start I'm in no way suggesting that this is the way to do it or is even a good practice. I'm just relating what I have found in this case and that I am surprised that the plywood has stood up so well to the elements.

 

[sphelps]

May have been a good quality marine grade ..

 

[gm280]

If the plywood had a good circulation of air drying it out quickly, I can see it going for a long time. In every rotted boat project, it is the water that sits that causes so much damage. And that holds true for homes or vehicles as well. Water is a very corrosive solution as we see so many time. Keep it dry and it will last... JMHO!

 

[bonz_d]

So after seeing this I don't think I'm going to worry too much about being caught out in the rain and being wet for a couple days.

I really do not believe that was marine ply. For one I don't think it would have checked as much as it did and secondly I've look before at marine plt and everything I've seen has been 5 ply's or better.

Anyway, I've finally got that pc. fitted for the bow and I think I'm just going to sand, fill and paint it for now. I'll try and get a few pictures of this pc and show the checking and sawed ends.

 

[bonz_d]

Pic's, sorry the one of the cut ends didn't turn out so well

 

[jigngrub]

That looks like pressure treated plywood to me, not something I'd want in my tinny... and probably why it has lasted with nothing but checking.

 

[Grandad]

Exterior grade plywood will last a long time, given half a chance. The first picture below is of the only piece of original 1972 1/2" plywood that I found necessary to replace. A metal Mirax gas tank sat on this spot, trapping water under it that eventually rotted the floor and corroded through the tank bottom. I was able to remove it without even removing the sidewall, it was so bad. However, when I got around to pulling the rest in 2013, there really was no more rot anywhere. The second picture is the underside of the forward segments that were still pristine. - Grandad

 

[bonz_d]

That looks like pressure treated plywood to me, not something I'd want in my tinny... and probably why it has lasted with nothing but checking.

Most probably is which is another reason why it's all coming out.

 

[Watermann]

I agree that looks to be PT ply, certainly not marine grade, even 1/2" marine ply is 5 layer. 3/4 marine is 7 layer. I think I would be tossing that piece off the SN quite a distance if it is PT ply.

 

[bonz_d]

Agreed not a good idea to use though I will as a temp until I finish the Alumacraft. Most likely only till the end of summer then it will be done properly. I've also got some old rubber 1/8" gasket sheets that I plan in putting in between the wood and the boat for now.