question on using MDO

[mound]

I'm making a sandbox cover for a local pre-school. I chose 1/2" MDO plywood for it's weight and resistance to water. Do the edges need any additional sealer or is the whole board impregnated with the resin that makes it MDO?

[jteneyck]

MDO is a reasonably high quality exterior grade plywood with a layer of impregnated paper on one or both sides, depending upon which version you buy.  The edges are no more durable to weather than any other exterior grade plywood, so you need to take extra care to seal them against water. 

John

[Steve N]

Agree with John. Check out this video, it's pretty cool if you've not seen plywood made, in making the MDO they just say it has a phenolic coat. They show it at the end, and you can see the faces are that MDO Yellow, while the edges are just XYZ Ply whitish yellow. They haven't got any finish, so you would need to do something. On MDO road signs, when they eventually fail it's from the edges where moisture get's in  between the plies, and causes it to delaminate. The link below has some do's and dont's and applications of MDO vs Ply.



Plywood vs MDO

[mound]

Nice video thanks guys.. I have some Anchorseal, that should suitably seal the edges? I'd say just paint it but once I deliver this I have no idea how the folks will or will not take care of it

[jteneyck]

Nice video thanks guys.. I have some Anchorseal, that should suitably seal the edges? I'd say just paint it but once I deliver this I have no idea how the folks will or will not take care of it

I don't think Anchorseal is going to provide long term protection.  If you are delivering it unpainted I think soaking/coating the edges with epoxy will seal the edges better AND allow the cover to be painted should they wish to do so.  Anchorseal will prevent paint from sticking.  It really needs to be painted (in addition to sealing the edges) for the best long term durability. 

John

[Steve N]

I have been using this stuff since they have been making the 1 2 3, before that we just used their sealer. I know of it on a whole lot of cinder block basements in and around Dayton Ohio, some for a long time. Those I still know living in those homes still have dry walls, and no problems. It requires really putting on a good coat, or sometimes 2, but once it's on, it will accept any kind of paint. You could use it, or just pass it along to the end user. We also used to use it on our plywood duck blinds, they were out in the water all fall, and then outside leaning against the barn the rest of the year. The last blind I built was used for 11 years, and then I gifted it to some of my buddies kids, I believe they are still using it, gotta be 25 years total. That is regular ply, not MDO.

[Lynden]

The couple of times I have used MDO for patio table tops, I sealed the edges with two coats of Titebond III. After sealing the edges, I primed the tops and then rolled on two coats of Behr Porch & Patio Floor Paint. Be sure to break the corners of the edges with sandpaper and fill any voids before sealing and painting.