MDO

[coach]

I am going to try a sign for my business using MDO. I purchased a piece of 4'x8'x 5/8"
How deep should I cut the letters?
When painted does the paper hold up outdoors?
Thanks,,,,,,,David

[tuck]

David, you are talking about MDO plywood, right? You want to rout it down with raised letters? If that's the case, NOT a good idea!

The paper covering on MDO (MDO stands for 'medium density overlay') is a resin treated paper overlay that gives the plywood it's smooth surface and makes it water resistant. If you want to cut the letters out completely and glue them to another substrate, that's one thing. But to rout the whole sheet down with raised letters,...no, dude. You're gonna get into voids in the plywood, it ain't gonna rout pretty, and you will have all but destroyed the properties of MDO that make it useful for many other things. Even if you cut through the letters and mount them to a more suitable substrate, you're gonna have to spend considerable time on the edges with filling voids, sanding and sealing that it's just not worth it in many cases.

Do yourself a favor. Spend some more bucks on this sign for your business and buy yourself a sheet of HDU (high density urethane) foam from your local sign supply store. If your sign is to be set between post, then hang on to the MDO and use that for a backer (to back up the foam by gluing the MDO to the back of it). If the sign is gonna be screwed to a wall, then get your money back for the MDO.

Good luck. We're here if you need us!

[Gary Campbell]

David..
The paper is impregnated with a phenolic type resin. That makes a very good surface for outdoor use. The weak spot is the exposed edges, so take extra care to seal them.

You will compound this problem by cutting letters into the suface and exposing more of the unprotected plys. Have you considered cutting your lettering out of signfoam and adhering them to the MDO? With the general rule of thumb being max cut depth half of the material thickness, adding even 1/4" thick letters to the surface may give the sign more depth and make it look richer. The cut in letters may cause the plywood to warp. By adding letters to, instaed of cutting them in, you may increase the life of the sign, so that in the end, it will cost less.
Gary