"sel1" writes:

Maybe someone out there knows what the trade name of this plywood is, but
I
was recently talking to a guy restoring a 1953 sail boat and on the deck
he
was using the plywood that they use for the large billboard signs.

MDO.

Lew

"Mike" writes:

Can you use any kind of plywood for boatbuilding ort does it have to be
marine ply? Surely if you are planning on glassing and painting a plywood
hull it wouldn't really matter?

If you are going to use it in the hull, marine ply is the only way to go
since it has no voids and can be bent in a continuous curve which other plys
will no properly do.

If you are talking structural core material such as bulkheads, floors and
sub soles, that's a different animal.

I used 140 sheets of 1/2", 4 ply, CDX plywood sheathed with 50 oz of knitted
glass and epoxy to build my boat.

In my application, could give a hoot less about the voids since the ply was
strictly core material, the glass carries the load.

HTH

Lew

"Lew Hodgett" ) writes:

In my application, could give a hoot less about the voids since the ply was
strictly core material, the glass carries the load.

the voids are where the rot begins. heat and moisture in those tiny air
spaces.

MDO plywood means "meduim density overlay". I read that it refers to a plastic
coating. It was developed for highway signs, those big ones you see on the
freeways, to be weather resistant. The main advantage is the nice smooth
surface for interior walls, er, bulkheads.

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"William R. Watt" writes:

the voids are where the rot begins. heat and moisture in those tiny air
spaces.

Since all exposed surfaces are sealed with epoxy before the glass was
applied, chances of rot are slim and none.

MDO plywood means "meduim density overlay". I read that it refers to a
plastic
coating. It was developed for highway signs, those big ones you see on the
freeways, to be weather resistant. The main advantage is the nice smooth
surface for interior walls, er, bulkheads.

Actually it's a paper covering available on either one side or both sides,
otherwise it standard exterior grade ply.

Nice stuff for making wood working jigs, but IMHO, a total waste on a boat.

Lew

"William R. Watt" wrote:

"Lew Hodgett" ) writes:

In my application, could give a hoot less about the voids since the ply was
strictly core material, the glass carries the load.

the voids are where the rot begins. heat and moisture in those tiny air
spaces.


I've recently carved up 6 sheets of 1/2" MDO and didn't come across
anything even resembling a void. Granted I didn't cut it into teeny
pieces but many of them were relatively small enough that I would have
expected to find a void were there any.

Actually I like it, at least the stuff I've used. All plies are even
thickness.

MDO plywood means "meduim density overlay". I read that it refers to a plastic
coating.

The coating is paper and there are 2 versions of that I'm finding. The
brown coating soaks upo epoxy like a sponge and I doubt it would itself
be waterproof. The green coating seems to be already resin coated as
epoxy will not penetrate it.

It was developed for highway signs, those big ones you see on the
freeways, to be weather resistant. The main advantage is the nice smooth
surface for interior walls, er, bulkheads.


I've used it for decks (glass covered) on power boats with no problems.

Brian Cleverly

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Medium Density Overlaid Plywood can usually be special ordered from
any retail lumber yard. Georgia Pacific now makes most of it I think.
I used to buy a brand called Roseburg and there were two grades,
regular, and "2-step" which is smoother with less voids.
The coating which is described as "resin impregneated fiber" looks like
brownish paper.
I've built boats out of it to save a buck and it works BUT....the
quality of MDO seems to vary. Occasionally there are rather large voids
in it. Generally the 3/8 inch thickness has no or very few voids and the
1/2 inch has more voids. The 3/4 inch is worthless. So if you want, say,
a transom that is 3/4 inch thick,sandwich two thinner pieces together
with epoxy. Also, MDO is available with the "paper coating" on either
one or both sides...specified P1S or P2S.
This plywood is generally high quality douglas fir, just like marine but
with an occasional void.
There is also an HDO plywood that is used for concrete form work. I have
never used it but its worth a look if you have a source.
The trouble with marine fir plywood is that it checks badly unless epoxy
glass coated.
In any case, I'd cover at least the outside with epoxy and glass when
using MDO.

sel1 wrote:
Maybe someone out there knows what the trade name of this plywood is, but I
was recently talking to a guy restoring a 1953 sail boat and on the deck he
was using the plywood that they use for the large billboard signs. It is
made to withstand weather after all. Cheaper than marine plywood too. Says
its not the first time he used it (not on the same boat either).


"Mike" wrote in message
...

Can you use any kind of plywood for boatbuilding ort does it have to be
marine ply? Surely if you are planning on glassing and painting a plywood
hull it wouldn't really matter?

steveJ ) writes:

There is also an HDO plywood that is used for concrete form work. I have
never used it but its worth a look if you have a source.

I looked at some at a constrcution site. They were delivering full skids
of it to use on a high rise condo. It was too thick and heavy looking lof
light boats. I copied down the name stencilled on teh side of teh skid and
looked it up on the Internet.There were no details about its compostiion
or characteristics. i can't remember what it was called.

In Asia they use a "plywood" made of bamboo for concrete forming. It is
said to last longer than fir plywood. Apparently they use it many more
times before they have to throw it out. It's made by weaving thin strips
of the tough outer layer of the bamboo into veneers which are glued
together in layers like plywood. I imagine that would leave an uneven
surface which would be filled with resin like fibreglass cloth, making the
"plywood" heavy. I looked up a supplier (Sino Forest) on the Internet. It
doesn't seem to come in thin sheets. It would be interesting to get one's
hand on a sample. Bamboo is a grass which growns very fast so it sounds
like a more "ecologically sustainable" material.

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On Thu, 23 Sep 2004 22:38:04 GMT, "Mike"
vaguely proposed a theory
.......and in reply I say!:

remove ns from my header address to reply via email

I post this because you have had many answers trying to help and in 6
days you have not bothered to reply.

Just imagine! You're put there

TROLLING

one day, and you hit a reef. Suddenly you think "Did my message REALLY
have enough irony in it to really satisfy me?"

And as your pitiful question sinks under the foam of well-meaing
replies, you SHOULD realise that really, the real thing is the only
satisfying thing!

Can you use any kind of plywood for boatbuilding ort does it have to be
marine ply? Surely if you are planning on glassing and painting a plywood
hull it wouldn't really matter?


************************************************** ***
I know I am wrong about just about everything. So I
am not going to listen when I am told I am wrong about
the things I know I am right about.

On 30 Sep 2004 13:25:27 GMT, (William R.
Watt) vaguely proposed a theory
.......and in reply I say!:

remove ns from my header address to reply via email

Nothing is ecologically sustainable when humans get hold of it....

Bamboo is a grass which growns very fast so it sounds
like a more "ecologically sustainable" material.

************************************************** ***
I know I am wrong about just about everything. So I
am not going to listen when I am told I am wrong about
the things I know I am right about.

Old Nick ) writes:
On 30 Sep 2004 13:25:27 GMT, (William R.
Watt) vaguely proposed a theory
......and in reply I say!:

remove ns from my header address to reply via email

Nothing is ecologically sustainable when humans get hold of it....

come to Ottawa and visit the Dominion Arbortetum

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