"Swingman" wrote in message
...
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.
First, thanks to all who responsed, and I'll answer the points raised here,
point-for-point, and others.
What is the "base" being used for?
A fitness-type "jungle jim", for hanging, swinging, etc.
Is proposed plywood being installed horizontally (as with a subfloor) or
vertically (as with siding)?
Horizontally, and in contact with backyard-type stuff: grass, soil, sand,
concrete, etc.
Will it be carrying weight?
Bodyweight, from kids up to 500# adults.
Which would sort of require that whatever surface is supporting this base be
pretty level, uniform.
If so, what is the sub-structure, and how much weight?
The units I've made already use "regular" 1/2 ply, which by itself is
absolutely inadequate for the job.
But because of "guy poles" (think guy wires, but rigid), and various gusset
plates, there is surprisingly little stress (at least bending stress) on the
ply. It serves more as a platform for screws/bolts, for the rigidifying
members..
The net result is to keep the apparatus itself from tipping over.
Will any part of it be directly exposed to the weather?
All of it, year-round..
That said, there is really no reason to use indoor plywood outdoors, and
to do so will ultimately be unsatisfactory regardless of the covering.
Well, this is the crux of my point. If indoor ply WERE sufficiently
"encased" in poly, or some epoxy/plastic coating, COULD it become
weather-proof? And at what cost?
I understand, now, from the other replies, that it would be better to start
off with a more appropriate class of plywood.
Really, the Q was sort of two part, asking about plywoods, and the
effectiveness of coatings.
Wolmanized wood sounds intriguing.
http://gawain.membrane.com/decks/lum...ized_wood.html
has a succinct description, and reflects what Jack was saying about
wolmanized wood.
There are other solutions, which includes making the base out of aluminum
plate, which I am actually in the process of doing, as a test.
Not cheap, tho, altho when one factors in the whole finishing process
required for wood (or perhaps the cost of wolmanized PT lumber -- haven't
priced this out yet), mebbe alum plate won't be that far off, price-wise.
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.
It's hard to imagine HD supplying ANYTHING of quality.
My understanding is that even reputable power tool companies (Bosch et al)
make HD versions.
But indeed, caveat emptor, and the more one knows, the better one can buy.
Easier said than done, however.
I am, however, a big fan of the Husky compressors that HD carries. Have
bought two, VERY quiet units (for compressors), and so far so good.
--
EA
--
www.e-woodshop.net
Last update: 4/15/2010
KarlC@ (the obvious)