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Catalina/Capri 25/250 Sailor's Forums

Catalina 250 Specific Forum

Difference between marine & exterior plywood

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Alan Therrien
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USA
113 Posts

Initially Posted - 12/13/2004 : 15:26:51

This is my day for dumb questions. Is there any difference between the exterior grade plywood available at Home Depot, or similar stores, and the marine grade plywood from speciality lumber yards? I am getting ready to cut a new V-berth cover, and was thinking of using exterior plywood.

All constructive comments are appreciated.

Alan Therrien
"Moonpenny"
C250K #418

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Oscar
Master Marine Consultant

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USA
2030 Posts

Response Posted - 12/13/2004 : 15:53:56

Yes, the glues in marine ply are water resistant. Supposedly the stuf will not fall apart when it get's wet. CAVEAT EMPTOR....not all marine plywoods are created equal. Some are much better than others...(I think Practical Sailor did some testing, not sure, check them out.) However, ALL marine plywoods are much more expensive than exterior grade. If there is only occasional, if any, water contact, as in a v-berth cover, exterior, or even interior (smooth) is just fine, especially if you give it a couple of coats of cetol and/or oil of some sort...(I like boiled linseed).

Oscar
C42 # 76 "Lady Kay" (Ex. C250 WB #618)
Georgetown MD/Fort Lauderdale FL

"Hindsight is 20/20, if I knew then what I know now, I would now be living on a small wooden sailboat, making a few bucks here and there playing a guitar and singing songs in bars."

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Alan Therrien
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113 Posts

Response Posted - 12/13/2004 : 16:34:08

Oscar,

Thanks much for the info. Perhaps I'll use exterior grade plywood and cover with a few coats of old fashioned spar varnish.

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Bay Tripper
1st Mate

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USA
56 Posts

Response Posted - 12/14/2004 : 08:55:46

If you use exterior grade plywood make sure you can replace it. The marine plywood will save you having to replace at a later time.

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bill bosworth
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172 Posts

Response Posted - 12/14/2004 : 09:45:15

Alan;
I've used exterior plywood to build several small boats, I've never had a problem with delamination. The glue used is generelly not the problem. Marine plywood is made from veneers that are void free, veneers in exterior plywood contain voids, the spaces that you see on the edges of the plywood after you cut it. These voids are great places for water to enter and cause the wood to rot, also when used for boat construction, these voids will eventually telegraph through the finish. For you application, exterior plywood should be fine. A lot (most) of the plywoods now are exterior grade, as the manufacturer only uses one type of glue, waterproof, and the dealers only have to stock one kind. Much of the luan plywoods, which are available in some places use waterproof gule. These are inexpensive and look great when varnished. If unsure, take a little sample and soak it in water overnight. I made a project from 1/4" luan, to check it I boiled the sample for about 1/2 hour with no delamination problems.
Bill, c250wb serendipity

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Ray Seitz
Captain

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USA
416 Posts

Response Posted - 12/15/2004 : 12:38:23

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">I've used exterior plywood to build several small boats, I've never had a problem with delamination.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Diddo, in my case work skiffs. I think all of the marine grades are designated as such for water/salt water applications. I do not think the marine grade classifications would be suitable for any application where skin contact is likely to occur frequently. Here is a link to the American Plywood Association website.
http://www.apawood.org/level_b.cfm?content=prd_ply_main
There are a lot of PDF format files/topics, which you can download or read online

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Alan Therrien
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USA
113 Posts

Response Posted - 12/16/2004 : 16:30:50

Thanks to all for your experience, suggestions and advice. It sure is great to have this site for our exchange of info specific to our model Catalina.

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tinob
Master Marine Consultant

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USA
1883 Posts

Response Posted - 12/17/2004 : 09:17:39

I have also used exterior grade plywood for marine projects. Used it for sailing skiffs and at least one clam barge. Lasted several years and then sold them. Problem free.

Marine ply uses several more plys for a given thickness than exterior grade and is, as mentioned, voidless. All plys back then ('60's) used the same glue, hexyl resorcenal...boy I apologize for that spelling, senior moment

It came as a two part glue in powder form.
Val on the hard DAGNABIT

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