On Thu, 07 Jul 2011 16:16:48 -0500, Steve Barker
wrote:

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.

A nice heavy coat of good old fashioned exterior paint will work
wonders. After all, that what is on houses. Throw some sand in if you
need traction control.

PS. i'd go 3/4". 1/2" is not good for much of anything.

I'd go at least 5/8" if not 3/4", and he can order pressure treated
exterior plywood from his lumberyard if they don't stock it. Spar
varnish over that, for the flexibility if offers, should keep the
platform solid for years and years. Be sure that the finish is well
maintained.

--
Happiness lies in the joy of achievement and the thrill of creative effort.
-- Franklin D. Roosevelt