Weather protection

[Charles Palmer]

A few weeks ago I replaced the stock plastic cover on out gas fire pit with one I made from recycled pallet wood. I planed one side and ran them through the jointer. I stained the top and sides, then several coats (top and sides) with spar urethane. I figured that since these were pallet wood, that'd be sufficient to protect the top. But after a day of rain, the top was warped like crazy. I hope that the attached pictures are clear enough.

my wife suggested and I'm inclined to believe, that leaving the bottom of the cover unsealed allowed moisture to get in from the bottom and expand / warp.

I sealed the bottom and it appears that the cover isn't warping as badly anymore.

now for the real question -
I'm making a corn hole set out of exterior 3/4" plywood. We anticipate storing the boards outside in the elements. What can I do to ensure that the set doesn't warp? I've used wood putty on the holes. I've given it 2 coats of sanding sealant. I've given top and bottom a good coat of exterior paint. And will give one more coat of exterior paint for the final colors...

Is this sufficient? What do I need to do to be able to store plywood projects in the elements?

thank you in advance for any help!

thanks,
Charlie

[Adam Herman]

always seal all sides to prevent warping.

film finishes will come off when they are outside, just a matter of when.

I have a set of outdoor furnature built from pallet wood, I used solid color stain on them and they look like new after 2 years. table tops are t&g pine and are have helmsman marine varnish and look great, but have always been on a covered patio. for stuff in direct sun I would lean towards an oil finish. I am trying cabots on a new set of tables for loml's parents that will sit in the sun 100% of the time at just over 8k feet of elevation.

[Mel Fulks]

Top quality coatings work well with TOP quality materials. They don't do so well on lesser stuff, but I don't know why. What I would do , and HAVE done is use Titebond 2 to cover all surfaces with "cotton duck" available at most fabric stores.
Then paint with acrylic paint. Thin first coat with 25 percent water. It's a very old method updated and proven. You can find some you tube info.

[Charles Palmer]

Thank you Adam and Mel!
Im going to seal the corn hole boards as best I can with exterior paint. Then I'll put a coat of spar urethane on top and bottom. Hopefully that'll make them last a few years.
ive got a swing set with a small deck between the ladder and the slide. I'm going to put a couple of boards under it and store the game boards under the deck. They'll still get some rain and sun (not direct) but not too much.

[Mel Fulks]

Charles, one of the videos is "poor man's fiberglass". It's not exactly the way I do it ,but principle is the same.

[John Blazy]

Mels idea is right on, due to the fact that the canvas holds the polymer in a structural way to bind the wood and physically keep it from swelling and delaminating. Also holds the polymer in a thick enough membrane to add to its water resistance.

If you really wanted to take this the best level, then epoxy with canvas is even better. Pre-soak the plywood in epoxy, then wrap in epoxy soaked canvas. Epoxy is the absolute #1 waterproof polymer, and no "exterior grade" paint, spar varnish or anything else will stop moisture from seeping in because of osmosis through the exterior paint.

but now you are getting into almost boatbuilding, so the project might not warrant the cost. But there is your answer.

All the coats of spar varnish in the world will just add to the headache when it cracks even the slightest bit, water seeps in and swells, opening the crack more, then you get peeling of all the coats. Epoxy soaks in and petrifies the outer 1/8" of material if applied right.

[Mel Fulks]

Good of you to help, John. Thanks. I sometimes lament how skeptical modern people can be about "new" info with a long proven history.

[John Blazy]

I think that if most woodworkers played with epoxy at least once in their ww career, they would realize just how versatile it is for lots of things. Not too hard of a learning curve either.

By a HUGE margin, my boat has been the absolute #1 most fulfilling project I have ever done, and continues to pay off in spades. And in my professional career doing insane kithens with Wenge inlays, a conference table for MTV, huge 700 lb color-changing light sculptures - all pale compared to my boat. I always encourage woodworkers to try to build their own boat - you can't overestimate the payoff.

I used over five gallons of epoxy on this. The rest was PL premium polyurethane.

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[Malcolm McLeod]

A couple of experiences with epoxy and outdoors - -
Years ago as Maint Mgr for chemical company making nasty stuff in outdoor steel vessels, we had to deal with excessive corrosion. Consults and quotes led to coating the vessels in a Sherwin-Williams white epoxy for its excellent performance on chemical resistance, mechanical strength, and durability. But (at the time) epoxy blows big time in the sun - - UV just eats it up! So we over-coated the epoxy with S-W white hi-build aliphatic polyurethane. It was weak with chemicals and strength, but excelled at UV-resistance. Combo cut our vessel maintenance efforts in half.

Personal build experiences with wood are that the less moisture that reaches the wood, the better - - whether you soak/swaddle it in epoxy, or sand & varnish every 3 weeks (i.e. a boat). Same for UV - the higher the coating's solids content, the less maintenance you have to do.

[Rich Engelhardt]

Top quality coatings work well with TOP quality materials. They don't do so well on lesser stuff, but I don't know why.

A typical film coat of material (paint/varnish) is roughly the thickness of a single layer of toilet paper.
Asking something that thin to stand up to the elements is asking a lot.

Same for UV - the higher the coating's solids content, the less maintenance you have to do.

Sort of - but - not really.
Solids content figures are only good for determining the rate of spread.
Mastics with a solids content of 99% (coal tar epoxies) can have extremely short lives outdoors - where they absorb nearly 100% of UV rays.
In underground facilities or inside potable water tanks - where they never see sunlight - they can last almost forever.

Not all solids are UV absorbers or UV reflectors. Matter of fact, very few of them are.
Solids are mainly where you get hiding power and film build from.

[Charles Palmer]

Thank you guys!