Marine vs Treated plywood

DSmith3426

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Mar 29, 1998, 3:00:00 AM3/29/98

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I need to replace the floors in my boat. The local lumber yard said both have
the same warranty, why should I pay a 100% premium when some say in this NG its
the same thing?

Rod Christel

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Mar 29, 1998, 3:00:00 AM3/29/98

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I have been told that the main difference between marine and exterior
plywood is that the marine stuff has tighter requirements about the size of
voids in the core layers. This is important when bending the wood around a
curve, but for flooring I can't see what difference it would make. The
people at the lumber yard should know alot more about it than I do though!

Rod Christel

DSmith3426 wrote in message
<199803290511...@ladder03.news.aol.com>...

Classic Boatworks of Maine

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Mar 30, 1998, 3:00:00 AM3/30/98

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Marine grade plywood is a type of plywood construction where all layers are
free of voids. any other plywood, has voids in the inner layers and is not
nearly as strong. The use of treated plywood must be matched to the
strength as it is not as strong as Marine grade ply. (Much of the treated
woods are poisonous to people - if you use them where the vapors will be in
an enclosed area - like a cabin - you may find yourself sick.)
Don't skimp on the cost of your wood - it is one of the smallest costs in
your boat.

--
Good Luck and Fair Seas
Marshall and Jo Duhaime,Jr.
Classic Boatworks of Maine - We build and restore classic wood boats.

DSmith3426 <dsmit...@aol.com> wrote in article

Goodchild

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Mar 30, 1998, 3:00:00 AM3/30/98

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Rod:

I believe there are four principal differences between conventional
exterior plywood and the "true" marine grade.

1. "True" marine plywood is manufactured with absolutely no voids in
the inner plys.

2. Marine plywood MUST use waterproof glues which pass the boiling
tests.

3. Marine plywood commonly has more plys than conventional exterior.
E.g., 1/4" marine plywood would have 5 plys while exterior only 3.

4. "True" marine plywood has the inner plys made of the same material
as the outer; no trashwood inner plys.

I have not used marine plywood in the building of Toad Hall. This is a
round-bilged hull (designed in 1883) entirely planked in plywood in a
cold-moulded manner. There are many small radii bends and in some cases
minor compound curvatures; marine plywood would not take these bends.
The exterior worked well however. The boat has two hulls separated by a
Girdle Frame and is sheathed in fiberglass on the inside of the inner
hull and on the outside of the outer hull.

I think the exterior will stand up well here!

Best regards,

David N. Goodchild
--
PART THREE of building TOAD HALL: The Rotating Building Frame
http://www.anyboat.com/toadhall.htm

For shop and building tips from TOAD HALL
http://catalog.com/bobpone/shopbuilding.htm

Mark Brueggeman

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Mar 30, 1998, 3:00:00 AM3/30/98

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DSmith3426 wrote:

> I need to replace the floors in my boat. The local lumber yard said both have
> the same warranty, why should I pay a 100% premium when some say in this NG its
> the same thing?

You don't say if you intend to glass the floors. If so, don't use treated wood;
the glass is unlikely to stick to it. Ditto if you're going to paint the plywood.

You can probably get by with AC exterior plywood if the floors are not going to
see much fresh water (eg rain). Voids in exterior grade plywood collect water
and are susceptible to rot. Sealing the wood with epoxy, especially the edges,
can help prevent rot.

George Burns

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Mar 31, 1998, 3:00:00 AM3/31/98

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Just a thought on your description of marine grade plywood. Last year I
went to Tacoma Plywood to purchase a sheet of 3/8" AB marine fir
plywood. What they brought out was three ply, with the two face veneers
being very thin. There was also a void running clear through the sheet,
in other words, I could see all the way through this void, from one edge
to the other! I would have been better off using 3/8 CDX!

Since then, I have wondered what the industry standard (if any) is for
marine grade fir plywood.

M DeMetz

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Apr 1, 1998, 3:00:00 AM4/1/98

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>Just a thought on your description of marine grade plywood. Last year I
>went to Tacoma Plywood to purchase a sheet of 3/8" AB marine fir
>plywood. What they brought out was three ply, with the two face veneers
>being very thin. There was also a void running clear through the sheet,
>in other words, I could see all the way through this void, from one edge
>to the other! I would have been better off using 3/8 CDX!
>
>Since then, I have wondered what the industry standard (if any) is for
>marine grade fir plywood.
>

That does not sound like marine plywood. It sounds like CDX that some one
ether mis labeled or passed off as Marine.

Dave Carnell

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Apr 1, 1998, 3:00:00 AM4/1/98

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Classic Boatworks of Maine wrote:

>

> (Much of the treated
> woods are poisonous to people - if you use them where the vapors will be in
> an enclosed area - like a cabin - you may find yourself sick.)

Treated plywood is treated with water solutions of CCA (chrome, copper,
asrsenic).
It has no vapors, so there is no hazard to people in enclosed spaces. If you
ate a lot of it, digestion would probably extract the poisons into your system,
but tests have shown that water will not extract CCA from sawdust of the
treated wood, so there is no hazard from bilge water coming in contact with it.

Paracelsus (~1500): "Everything is a poison; it is just a matter of the dose.

Dave Carnell, ancient alchemist