MDO Plywood

Does anyone have any experience using MDO Plywood? I am having difficulty finding quality exterior grade plywood in my area, but everyone seems to have MDO. Anyone used it on a hull?

 

Chris craft used it in all the SeaSkiffs. It works fine above the waterline.

 

mdo

I built a basic hull in 1999 using mdo, and I've been very satisfied. It has never checked or separated, and I use simple exterior latex as a coating. It's spent plenty of time in salt and freshwater. I can find all the good exterior ply I want in the area but not mdo. Sure envy you. George Buehler notes that Chris-Craft used mdo in many boats built in the '50s, many of which are still in use.

 

MDO satisfies the APA (American Plywood Assoc.) marine requirements and usually carries that grade from them. Not all MDO is created equal, I've seen some real good stuff and some pretty marginal stock over the years, so shop carefully and you'll do okay.

I use the stuff all the time and like it. There was a time when there was a big difference in pricing between it and other more traditional marine grades, but that's changing. I just got 12 sheets of good 1/2" BS1088 Doug fur out of Miami at 20% less then I'd been spending for MDO and this is better stuff, so . . .

MDO on the bottom is okay in some applications, but it depends on the construction methods, the strength its providing the design and the amount of warping you'll need to do getting it to flow around the hull. If the planking requires a lot of twist, you may find a better quality marine grade ply the way to go. You'll have less breakage and it does seem that MDO has more flaws and voids then the higher priced stuff, which is where you'll run into trouble when bending.

My Sea Skiff (27' - 1960) was replanked and then sanded heavily before I got it. They used Doug fur and the topside planks look like a washboard. I'm slowly smoothing them out, but MDO would have saved a lot of this work in the first place. Replanking would have almost been worth the effort, but I'm getting real good at smearing on the filler, just so as to not require to much sanding.

 

looking for MDO

When in search of MDO Shop your local sign supply warehouse. We stock it by the skid. PAR has a good point as the quality of the stuff has declined badly over the last few years. When I started painting signs 15 years ago the stuff was mahogany 7 plys for 1/2" very stable and rarely warped. Now the stuff I stock is 5 ply fir, full of voids and 50.00 a sheet..... I would urge you to get the G2S (good 2 sides) this helps the warp factor as both sides will deal with moisture at the same rate. If your looking to knock together a skiff to get on the water with an A- finish you cant go wrong.
places to look...
east coast Beacon Sign supply
mid west Midwest sign supply
Denco sales
Pacific NW Sun Supply
Hope this helps a little 8Kts

 

Thanks to all for the feedback. Although I have already moved forward on this boat, I think I will use MDO on the next.

How bad do you have it when you have not even finished the first boat yet and you are already planning for the next?

 

Quite normal . . .