Tamara-Interior Plywood question

[Woodonwater]

The week end was spent basically gutting Tamara to expose the full length of the bilge. The build-up of 60+ years of sawdusty scudgey stuff was amazing. She is all scraped clean and will be red-leaded as soon as I haul her out Nov. 9th. (It was to be Oct 19th, but my boatwright was delayed).

I pulled alot of wet and moldy wood out of her. The original ply had delaminated badly and had white moldy spots. I saved them for template purposes only. After seeing what came out of her, I am loathe to build back in anything not marine ply or fir soaked in epoxy. However, I have some excellent plywood that I am considering using. It came out of a 1950's house (by the beach) and was the closet doors. It is in excellent shape and has always been fully sealed with paint. I doubt if it's marine grade-how do you tell?

Anyway, this plywood has a heft to it. It's not the soft, mashy crap one buys today made from 5 year old trees. I haven't bought marine ply yet, and I wonder if it is soft 'crap' just like Home Depot ply. My thought was to use my old ply for interior bulkheads and cabs. I would be sure to seal ALL new cuts and add another level of paint overall. What do you guys think...Is this suitable for interior work on a 37' sailboat?

Am I asking for more trouble like I just ripped out?

Thanks,
James

[Lewisboats]

Your interior door plywood probably doesn't have glue that is waterproof...not something I would want to put into a boat. Better off with marine ply. Try soaking the edge of a piece of scrap a few times...see if it delaminates.

[JimD]

What colour are the glue lines? Urea formaldehyde glue is typically used for interior ply, is light in colour, and not water resistant enough for marine use. Phenol formaldehyde glue is dark in colour and is used in exterior and marine ply for its far superior water resistance. There are other glues and considerations such as glue fillers that weaken the bond, but most likely if you have a dark glue line its PF and good for exterior and marine use - I think. ;)

[Woodonwater]

Jim,
Interesting info. I had heard that all, or at least most, plywood made today uses exterior glue, which I guess is PF. Is that true?

I will check the glue lines of this old stuff. Likely I 'll play it safe and get marine grade.

I was told that it's much cheaper to buy marine ply from Oregon than it is from California. Does anyone have experience with this?

[JimD]

Woodonwater. Yes, cut through a piece and see what you've got. What you want, ideally, is dark glue lines (PF), no voids, and layers of equal thickness. If you have all that then there's a good chance its better quality than most of what you can find today at any price. I be no plywood or glue expert, but from what I've heard UF glue can give off formaldehyde gas (poisonous) but PF doesn't, which is a good reason to use the better glue even for interior applications.

[Woodonwater]

I wondered about the off gassing issue. Perhaps that's why most ply now is PF, not UF? I know cabinets for houses are increasingly going non-formaldehyde, but I suspect any 'greening' of adhesives or sealers on boats will produce inferior results.

James

[Woodonwater]

I don't want to threadjack the other guy discussing marine ply, but I have to redo the deck on Tamara, 37' ketch, and am wondering exactly what to use.

My guestimate is that I'll use 3/4" okume or doug fir. I will glass the top and paint the bottom. I never thought about MDO or Superply-whatever that is. How about Appleply? That is beautiful stuff, hardwood, no voids...but probably not the right glue.

I was offered some baltic birch ply, sized in metric, which is over 1" thick. Looks like great stuff, but maybe too heavy for the deck, and looks to be very difficult to bend. Tamara originally had 3/8" ply and 1" mahogany deck planks, now badly rotted.

[JimD]

... I'll use 3/4" okume or doug fir. I will glass the top and paint the bottom.

DF ply tends to look pretty bad with just a coat of paint on it.

[Ron Williamson]

Don't use the birch.
MDO is a better option,but some mills I'm told are using poplar(or aspen?) for the core.
Just a few minutes in a microwave,in a glass of water,will tell you if the glue is decent.
I cooked up some birch,5/8"fir underlay(According to the printing on the edge) and some MDO.
It wasn't very long(a few minutes) before the birch looked like lasagna.
The other two,I cycled(heat until the water boils, then let cool for a while)until I got bored(a few hours off and on over a couple of days)and aside from being wet,they were as good as new.
R

[Lewisboats]

Jim,
Interesting info. I had heard that all, or at least most, plywood made today uses exterior glue, which I guess is PF. Is that true?

Yes it is true...but the stuff you are talking about was made 50(+) years ago didn't you say? Not exactly today. The veneers are probably much better than what is available today but I don't know about the glue used.

[Eric D]

Take the birch and keep it for inside your house or for jig making, but for heaven's sake, NOT in the boat.

MDO is a good option, otherwise marine grade ply. Not a fan of the Doug Fir I have seen locally, sales guy was even pretty down on the stuff (but hey, it is local and no shipping charges so it can't be that bad right?)

you are spending the time and the money to do it up right so IMHO do it all the way......

[Woodonwater]

OK, I will cook up a piece of the 50+ year old stuff and see how it does. I think I'll pop some bronze in the oven to strip the paint while I am at it...my girlfriend will be thrilled!

So, no mention of Merranti for the deck? From Boulter Plywood, this stuff in 3/4" is the same price as DF. Why not?

Okoume is not too much more either. I am inclined to bail on the DF. It sounds like crap, which is sad. Growing up, when someone bought "marine grade ply" they were getting 'the best'. Apparently that just ain't so anymore.

On the interior, if my 50 yr old stuff can pass the cook test and has what looks like PF glue, then I will use it and seal it up well. I will then face it with 3/8" or 1/4" V groove panels in pine, fully primed or dipped in epoxy and glued or nailed on ply face, then painted glossy white with bright mahogany trim.

I still can't get past using the MDO on the deck of a sailboat. How could this not suck up moisture over time? Will it take up epoxy to protect it? How about HDO (which is a thicker layer of fiber veneer)?

A note about the birch...This stuff was bought by the previous owner of Tamara, who was an excellent boatwright. I may have the name off a bit, but I think it is a marine grade ply. It's too thick, but is it not a material to consider here?

James

[Eric D]

I love meranti. Bit heavier per sheet than Okoume, but has better theoretical rot resistance. I would go for either of those in a heartbeat. Given the idea of decks, laying flat and all, I would go with the meranti for the rot issue. Others may vary, but that is my opinion. If it was the wheelhouse etc, vertical/above water structures, then the Okoume wins. DF out...MDO is better than you think.....think of all those signs for all those years out in the elements....without ROT or delamination...Can't be many situations worse than a Northern winter with snow, then warm days in the 40's, then freeze at night, then thaw, then hot humid all summer in the blistering heat......and they make it...I think if you encapsulate in epoxy you are doing fine.....