"Jack Stein" wrote in message
...
On 7/7/2011 4:52 PM, Existential Angst wrote:

I'm looking to make a 4 ft x 6 ft base for some apparatus, out of 1/2"
plywood, for outdoor use. It works well indoors, but I'm wondering if
I can make it *truly* waterproof for outdoor use, with enough coats of
poly, epoxy, or some clear plastic
coating-type finishes I've seen.

Wood is pretty much waterproof already, glue not so much. Outdoor plywood
uses water resistant glue, so it won't come apart so easily. Marine
plywood uses a good quality water proof glue and has no gaps in the
veneers for water to hide in. Marine plywood is rather pricy and probably
not needed for "some apparatus", whatever that is. I have bought 3/4
wolmanized plywood at my home depot, and used it for the walls on my
swimming pool. It has held up fine w/o any finish.

You put this wood IN the pool, to actually contain the water mass??
Details, please!!

And I guess this is not that unusual, given wooden-hulled boats, and the
roof-top water tanks you see in NYC.

What types of wood are used in wood boats, water tanks?


If I
were making a "base for some apparatus" I'd likely look into the 3/4"
wolmanized stuff. I would not likely use 1/2 inch for a base.

Weight is an issue, and it appears that structurally, I can get away with
1/2".
3/4" is of course an option, perhaps "heavier duty" versions".


Not that familiar with wood/coatings, beyond having done my floors
with a water-based poly+catalyst, with mixed results.

The nice thing about the wolmanized stuff is there is no need to try to
protect it with finish. You can finish it for looks,with paint or stain,
but that is up to you. Actually, I guess that's true with any quality
outdoor plywood.

Also, I know there's HD 1/2 plywood, which you can break across your
knee, and there is real 1/2 ply, from a lumber yard.

All plywood is "real".

Are there even harder/stiffer grades? I'm not necessarily looking for
furniture-grade plywood, but maybe that is indeed the stiffest

Yeah, 3/4" is stiffer, but really, there are a myriad of grades of
plywood, and all sorts of different cores for different purposes.
furniture grade is not what you are looking for outdoor use for an
"apparatus" base.

I was under the impression that for a given thickness, the more layers in
the ply, the stiffer it was.
However, I was actually testing pieces of ply I have laying around, and a
3-layer ply was signficantly stiffer than a piece of 4 layer ply, both 1/2"
And just now I roughly tested two pieces of 3/4 ply, one with *eleven
layers*, the other with 5, and the 5 layer piece feels a little more rigid!!

So I guess that theory is not reliably true.


. Cost, bang for the buck is a factor.

My home depot often has great quality plywood at great prices, but not all
the time. Right now they have some sort of "heat treated" stuff on sale
I've never seen before. It's red-ish stuff, I think outdoor.
I'd look into it if I were building an outdoor base for an apparatus.

I'll check it out.
--
EA



--
Jack
Got Change: Democratic Republic ====== Banana Republic!
http://jbstein.com