On 7/7/2011 3:52 PM, Existential Angst wrote:
Awl --

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.

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

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. Are there even
harder/stiffer grades? I'm not necessarily looking for furniture-grade
plywood, but maybe that is indeed the stiffest. Cost, bang for the buck is
a factor.
Maybe other "engineered products"?

Appreciate all input.

You simply do not give enough information for anyone to make an informed
response that will stand the test of time.

What is the "base" being used for?

Is proposed plywood being installed horizontally (as with a subfloor) or
vertically (as with siding)?

Will it be carrying weight?

If so, what is the sub-structure, and how much weight?

Will any part of it be directly exposed to the weather?

That said, there is really no reason to use indoor plywood outdoors, and
to do so will ultimately be unsatisfactory regardless of the covering.

There are any number of types and dimensions of plywood/sheet goods made
for "exterior" use, which will serve you better.

Also, the very same folks who supply HD and Lowes with sheet goods also
supply "lumber yards" with same (and just because you buy sheet goods at
a lumber yard doesn't mean it will be quality merchandise, particularly
in this day and age), so don't rule out the big box stores for good buys
on sheet goods. CAVEAT: you need to be familiar with the materials, and
how they are made, to determine what is acceptable.

--
www.e-woodshop.net
Last update: 4/15/2010
KarlC@ (the obvious)