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Teak Plywood - Marine Ply or Not?

Jan 13, 2015
60
Hunter 34 Deep Bay, BC
I have an '83 Hunter 34 (H34). The interior is entirely teak. One piece of 1/2" teak plywood on the bottom of a settee is completely shot. All the glue between the layers has given up, there is a bit of rot, and there is considerable damage to the teak side. I have that settee apart now for other reasons, so I plan to replace that piece. Interestingly, there is not another piece of plywood on the boat that I've found similar degradation; everything else is in pretty good shape.
It turns out that teak plywood is easy to get around here - except it's all cabinet grade, not marine grade.
I can't find anyplace local (Vancouver Island) that sells marine grade teak plywood. In fact, I haven't found anyone in Canada that does. You can get teak and holly for flooring, but not straight up 1/2" teak marine plywood. And the idea of shipping a piece of plywood from the US East Coast to Canada's West Coast seems ludicrous.
This piece is not terribly difficult to replace; it's rectangular with a single fitted edge. How much of a risk might I be taking to use cabinet grade plywood instead of marine ply? Barring a major malfunction, this piece shouldn't ever get wet. It should only have to deal with the normal humidity you encounter on a boat. If it disintegrates again, replacing it will be relatively easy.
Comments appreciated; you're welcome to tell me I'm crazy, or where to buy the good stuff.
 
Jan 11, 2014
6,322
Sabre 362 113 Fair Haven, NY
At least down here south of the border, cabinet grade and marine grade plywoods are very similar. The 2 main distinguishing characteristics are the number and size of knots and voids and the number of plies. There may be a difference in the glues that hold the plies together, but I'm not certain.

For a settee front, I would be very comfortable using cabinet grade plywood instead of marine grade. I would want to lean towards a hardwood cabinet grade rather than a softwood. After the piece is cut and dry fitted sealing the raw edges with epoxy might help prevent future delimitation.

It would be worthwhile to track down the water source that caused the original plywood to delaminate and fix it.
 
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Oct 19, 2017
6,501
O'Day 19 Littleton, NH
I think you have it right. Marine Plywood is used as a matter of course but it is intended primarily for hull construction. Seal your panel well. If it's not structural, replacing it will be just as you said. It isn't likely to need it though.
I'd look into why the panel went bad to begin with. Sounds like a leak needs attention or a hatch was left open in the rain and it didn't get dried out.
Save yourself the money and use what is available.
- Will (Dragonfly)
 
Jan 13, 2015
60
Hunter 34 Deep Bay, BC
At least down here south of the border, cabinet grade and marine grade plywoods are very similar. The 2 main distinguishing characteristics are the number and size of knots and voids and the number of plies. There may be a difference in the glues that hold the plies together, but I'm not certain.

For a settee front, I would be very comfortable using cabinet grade plywood instead of marine grade. I would want to lean towards a hardwood cabinet grade rather than a softwood. After the piece is cut and dry fitted sealing the raw edges with epoxy might help prevent future delimitation.

It would be worthwhile to track down the water source that caused the original plywood to delaminate and fix it.
Thanks for that. The local specialty plywood guys here tell me the principal difference with marine ply are (1) as you said, no voids, and (2) waterproof glue. They've never mentioned the number of plys as being significant.

There is some evidence that some of the fittings on the holding tank that lives inside this settee leaked at some point in the distant past. Until I disassembled the settee for other reasons, there was no simple way to get inside there and inspect it. When it goes back together, it will be modified so that it's easy to take apart and reassemble the next time. There was also a leaking portlight nearby, but I don't think that would have reached this piece (and all those leaking portlights have been fixed).

I really like the idea of sealing the edges with epoxy. I think that would make it pretty much bulletproof. Thanks a lot.
 

SG

.
Feb 11, 2017
1,670
J/Boat J/160 Annapolis
I would seal the back of the plywood along with the edges with troweled-on West Epoxy if you're going to be putting non-marine grade plywood in.
 
Jan 11, 2014
6,322
Sabre 362 113 Fair Haven, NY
Thanks for that. The local specialty plywood guys here tell me the principal difference with marine ply are (1) as you said, no voids, and (2) waterproof glue. They've never mentioned the number of plys as being significant.
I could have been clearer in my first response, both marine and cabinet grade plywood have more plies than construction grade plywood or ordinary plywood. The greater the number of plies, the more stable the plywood.
 
Oct 19, 2017
6,501
O'Day 19 Littleton, NH
Cabinet grade plywood should be void-free also because joinery work requires it. The difference is primarily in the glue.
- Will (Dragonfly)
 
Aug 20, 2010
1,399
Oday 27 Oak Orchard
Perhaps I can assist. The teak plywoods readily available are decorative marine teak plywoods. They consist in most cases of kapok (Cork) cores. These are specifically not for any structural component. Marine plywood has to have hardwood cores that are void free, fungus resistant and not waterproof glue but boil proof glue to conform to BS1088 standards. I went down this road during my restoration project. True marine teak plywood is horrifyingly expensive and not readily available. Okuome marine plywood from several manufacturers meets the BS1088 standard for structural applications and is easily obtained. It is mahogany so a bit lighter than teak but will provide a suitable substitute. You can stain it to match though the grain will be somewhat different.
 
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Tricia

.
Jun 4, 2004
78
Freedom 30 Victoria, BC
Have you talked with the folks at Westwind Hardwood in Sidney? While they have only cabinet grade teak plywood on their website, they’re very familiar with marine applications.
 

CYQK

.
Sep 11, 2009
461
beneteau first 42 kenora
Ordered teak plywood from windsor plywood and it came in from vancouver give them a call
Soposed to have the good glue
 
Jun 9, 2008
1,622
- -- -Bayfield
I've been doing this a long time and I totally recommend a marine grade plywood regardless of the veneer. It's all about the glue which is either waterproof or not and you want waterproof - even if it is not obviously subjected to moisture. There are home building exterior plywood that uses some sort of waterproof glue, but it ain't the same as marine waterproof glue. Ambient humidity exists in boats and if you have two pieces of wood glued together that is using something other than a marine grade waterproof glue, I can almost guarantee they will separate. The same with plywood. It will give you problems and if you are spending a lot of time and money to replace a bulkhead, for example, then you will not be happy if it starts to fail on you and you have to do it all over again. If the woodwork will be exposed to moisture for sure, then I recommend sealing the end grain or tabbing it in with fiberglass, however appropriate to further your cause for success.