Medium density overlay is a plywood product with a multitude of applications. Commercial contractors and those in the home building industry use MDO as an all-purpose, durable material. Designed for exterior use with waterproof glue, it's also used for interior purposes where moisture is present, or anywhere plywood is used.

NJ Turnpike
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Two green signs above a section of a freeway

MDO Anatomy

The core of medium density overlay plywood is made of wood layers and resin, laminated together with hydraulic pressure and heat. With individual core layers placed perpendicular to each other, and overlay coatings made from waterproof resin-impregnated fiber, this product is a weather-resistant incarnation of standard plywood. The combination of core layers and overlay provides durability to these standard-sized sheets. With an opaque surface that appears similar to paper, you might see faint signs of wood grain. Available with one or both sides covered with overlay, the material cuts, shapes, mills and drills using ordinary woodworking equipment, just as with any other plywood product.

Sign Material

Also sometimes referred to as signboard, MDO plywood offers a reliable material for making signs because of its moisture resistance and durability. Highway departments nationwide typically specify signs made from this plywood product. Because it's dimensionally reliable -- and free of knots and patches -- the inner core of MDO is dense and consistent, typically without significant defects. When the resin overlay is added, the material provides a slick and smooth surface ideal for paint and lettering. Routed letters, corners and edges remain clean and resist chipping and splintering.

Concrete Forms

As an ideal product for concrete forms because of it's durability, strength and water-resistance, large and complicated forms built with MDO can be assembled, torn down and reassembled. The smooth, slick surface imparts a consistent, even surface to the face of concrete. The insulating properties of MDO also lead to consistent, controlled drying times for concrete. Cleanup goes faster because the concrete washes or scrapes off easily from forms made with this plywood.

Siding Material

As a siding material, the product is attractive and easy to maintain. It accepts any kind of exterior paint, but it's also acceptable to leave it as-is in areas that are hard to reach or not highly visible. With insulating properties similar to natural wood, MDO provides temperature control to homes and buildings. Other exterior applications include using the plywood for fascias, soffits, chimney enclosures, gable ends, garage door panels and even fences.

Interior Applications

Interior uses for MDO plywood include cabinet jambs and countertops, structural panels, wainscoting panels, shelves, storage racks, bins, trims and molding. MDO isn't typically useful for woodworking projects that display grain patterns, but when painted, it presents smooth, even surfaces that are easy to keep clean.