Will plywood be ok outside if painted?

[Hoang N Nguyen]

I just picked up a big green egg and need to start building a stand for it. I plan to use exterior grade paint as my finish and was wondering if that will be enough to protect my plywood from warping. I plan to do a big pine laminated top and was wanting to use plywood for the sides, back and bottom. I had plan for the face frame to be made of S4S pine from the big box store as well as for the rail and stile of my doors. Pretty much the whole project will be pine and plywood, everything will be covered in 2 - 3 coats of exterior grade pant. Will this work or am I asking for trouble?

[Steve Schoene]

There is plywood and there is plywood. The typical fir plywood from your big box stores may have exterior glue, but is still only marginal for outside use, and would need a very good paint job. But fir plywood doesn't paint very well, with the grain telegraphing itself through multiple paint layers, barring tedious filling. The pine for face frame and door parts is also not a very good choice--the first break of a paint film will set off a sequence of rot and deterioration.

You will be much happier if you choose better exterior woods. For plywood, MDO (medium density overlay) has a smooth surface that takes paint very well, and interior laminations that hold up better. Cedar, redwood, cypress or white oak will all work better and hold paint very well compared to the pine.

[Mel Fulks]

Don't think it will work for long. Especially the horizontal surfaces. There are a lot of expensive ways to make something
like that last, but I only know of one inexpensive way. Glue light canvas (cotton duck available at fabric stores) with Titebond 2 to all surfaces and paint. Painted canvas has proven record over several hundred years.

[Howard Acheson]

Use Exterior rated plywood. Standard plywood is not rated for exterior use and paint will not adequately protect it from moisture.

[Hoang N Nguyen]

Thanks guys, I was afraid it wouldn't last so I ended up getting 2x8 cedar for the top and 1 by cedar for all the doors and panels. Also picked up 4x4 cedar post foe the legs as well. It's all rough cuts so I have a lot of jointing and planing to do.

I only asked about plywood as it will make the panels and sides go faster instead of having to mill everything and build up the sides one at a time. I also don't want to see any seams so I have a lot of glue up to do for making the side panels. I was hoping to finish the stand in a weekend or 2 but this will drag it out a bit longer

[John TenEyck]

As recommended, use MDO for the panels and seal all the edges before assembly. MDO is used for exterior signs and lasts a really long time when properly finished. I made some porch columns with MDO about 3 years ago, and they look perfect.

John

[Wayne Cannon]

I'll be a third to recommend MDO plywood for exterior use. As Steve mentioned, it's made for signs. I used some 1/2" MDO plywood for temporary gates -- untreated, unpainted, no edge treatment, nil, nada. After four years of temporary exposed to rain and sun, they were just as flat as when I first installed them. The brown finish had sun-bleached to a milky tan, but that was all.

If you get so-called "exterior" plywood, be sure to get it from a reputable source that doesn't import from Asia (i.e., don't use Home Depot, etc., plywood). I had a sheet of imported 3/4" CDX warp by over one foot when left exposed under the eaves (unfinished).

[Hoang N Nguyen]

I just called my local lumber yard about this MDO product and told them what I intend to use it for. They said it would work but I had to be careful with sealing the edges of it or else it would still peel off over time. I got a pretty good recommendation from them though, they said I can always use hardy board/plank from my local home store. I never thought about using hardy board for exterior paneling. The siding on my house is built with that stuff and it's suppose to last longer then me!

What are some thoughts from you guys about using hardy board for my side and bottom panels?