NON-marine plywood? (all input appreciated!)

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sophus_tree
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NON-marine plywood? (all input appreciated!)

Post by sophus_tree »

Hi Folks,

I am new to this forum and new to boat-building, so I am seeking some no-nonsense advice.

Some folks I recently met and befriended are about half-done building a Viking longship that I am really excited about.

However, they are building it using non-marine plywood for the ribs and lap strakes (though they are covering it generously with epoxy).

My concern is that the epoxy will crack in transport or use, thereby exposing the plywood to water, and the plywood will eventually de-laminate or rot.

I see a lot of posts on this board about plywood and not all of them mention the plywood being marine grade. Is non-marine grade plywood common to use in boat construction?

What do you all think? Any and all input appreciated!

-Michael Sweet
Last edited by sophus_tree on Sat Feb 21, 2009 9:44 am, edited 3 times in total.

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Bill Edmundson
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Post by Bill Edmundson »

Michael,

Many have used exterior grade instead of marine. My biggest problem is that the exterior grade, that I've found, isn't worth a crap. Too many voids.

I'm not the expert on this. I'm going to look at some lower grade marine grade this week. But, I like BS1088 and BS6566 marine. These are a joy to work with. BS1088 is the best. You'll pay for these though.

Bill
Mini -Tug, KH Tahoe 19 & Bartender 24 - There can be no miracle recoveries without first screwing up.
Tahoe 19 Build

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sophus_tree
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Thanks!

Post by sophus_tree »

Thanks, Bill!

By voids do you mean knots?

Any advice for how we might best move forward on this half-done plywood boat?

I am all ears. :-)

-M
Last edited by sophus_tree on Sat Feb 21, 2009 9:45 am, edited 1 time in total.

rasorinc
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non marine ply

Post by rasorinc »

CCX ply uses the same adhesive as marine ply. CCX PTS (plugged, touched and sanded). The exterior sides are filled with a wood plug (actual wood) and the inside voids are supposed to be filled with an adhesive filler. There are good and bad suppliers so you look for the stamps. I'm going to use some CCX PTS in my build but I know good from bad ply and I will oversize it by 1/8" and give it 3 coats of epoxy.
So if the plan call out 5/8" ply I will use 6/8" ply. CDX is interior ply and the adhesive is not waterproof.
Just more info for you. Yes, voids and plugs usually are where a knot was.
Wood lasts generations.

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sophus_tree
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Encouraging

Post by sophus_tree »

Thanks! This is encouraging. :D

I really appreciate the input.

-M

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sophus_tree
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Stamps

Post by sophus_tree »

There are good and bad suppliers so you look for the stamps.
. . . by this you mean look for stamps that say CCX PTS?

Hope I am not asking stupid questions. I am new to all this.

Thanks again.

-M

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Bill Edmundson
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Post by Bill Edmundson »

By voids do you mean knots?
By voids I mean nothing there at all. Go oto the box store and look at a stack of plywood. You'll see holes. BS1088 is supposed to be void free. BS6566 has a very very low % allowed. But, usually you won't find any.

The piece of 3/4" exterior on the transom of the mini-tug I'm doing had a void on an inner ply that was an inch wide and 15" long. When I filled it with epoxy I could see the extense on the surface ply.

Bill
Mini -Tug, KH Tahoe 19 & Bartender 24 - There can be no miracle recoveries without first screwing up.
Tahoe 19 Build

upspirate

Post by upspirate »

If you look at the end edge of the ply,you will see voids in the inner plies.They will run from edge to edge,not a hole in the face.

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Gayle Brantuk
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Post by Gayle Brantuk »

Michael,

We would never recommend plywood for the frames of any boat--with lapstrake, the planks are fastened to the frames and getting a screw to hold to the edge of the plywood is very iffy. As for plywood for the planks, as stated by these very knowledgeable guys, marine and exterior both have waterproof glues, the difference is with the voids found in exterior.

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Caber-Feidh
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Post by Caber-Feidh »

Once in a while you can find a B core ply in the box-stores. All NA made ply is grade-stamped with 3 letters. The first 2 are the face veneer grades, the 3rd is the core grade. The box-joints usually just advertise the faces. If you see an X in that last spot the cores are little better than firewood.

You really need B or better cores for any sort of quality.

Ply frames would be useless in most construction.

RoyH
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Post by RoyH »

Can you put in some pictures of the boat and some pictures of the frames etc.
Here on the Glen-L site there are many people who knows a great deal about building boats with plywood. You will get some solid input.
I'm just a starteled bunny in the headlights of life..

GJBan
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Re: NON-marine plywood? (all input appreciated!)

Post by GJBan »

What about Ultraply XL by Mooreland Co.?

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