MDO (Medium Density Overlay)


For more information including the APA rating of MDO click here.

What exactly is MDO, or Medium Density Overlay and why is it used?

Because many homeowners and contractors are unfamiliar with MDO we have provided the following information. MDO is ONE of the options available in our Thinline siding. The other option is "Breckenridge." If you would like to see a comparison of textures between the MDO and the Breckenridge products click here for a side by side view.

MDO is the abbreviation for Medium Density Overlay. MDO is a very high quality exterior wood product that has been used in siding applications, and on exterior signs. In fact, before aluminum was used for road signs, Cal Trans used MDO for many of its freeway signs. What many people do not realize is how weather resistant it is once is it properly primed and top coated.

The surface is laminated with a resin impregnated fiber. We admit it looks just like green paper, but it is much more than that! The resin creates a very weather resistant barrier that when primed and painted, provides one of the best water and UV resistant surfaces. We emphasize that it still must be primed and painted according to industry standards. Never allow it to get wet before being painted.

Since the original Thinline Eichler Siding had a smooth texture, some homeowners prefer the smoother surface of MDO. However, some customers feel that MDO is too smooth. However, if the primer is applied with a thick napped roller, a slightly rougher texture will be the result, and you will find that your new siding will match the original remarkably well within acceptable margins.

The draw back to MDO in addition to the ultra smooth surface is that it is 1/2" thick. This is good in that it often matches old Eichler siding better at the joints. However in some cases (such as an entire room addition) one might be better off using our Thinline pattern milled out of "Breckenridge" siding which is 5/8" thick because it has better shear strength. As is often the case, a fully qualified contractor can often help you decide which is the best choice for your situation.

Finishing
Crezon® MDO panels take paint uniformly with good chemical and mechanical adhesion. Paint lasts approximately three times longer compared to raw plywood under normal weathering conditions. Use top quality coatings and follow manufacturer's instructions. Avoid oil base stains, shake and shingle paints. All edges should be sealed.

The prime coat is the most important coat. Oil/alkyd primers are recommended; latex primers also work well. The surface should be clean and dry before painting. No other surface preparation is needed. Do not apply too thin a prime coat. The primer should be applied to yield about 1 mil dry film thickness. Apply within the spreading range recommended by the manufacturer to obtain proper thickness.

Top Coats
Once Crezon® MDO has been properly primed, it may be top-coated with a variety of finishes including solvent-thinned and water-thinned paints and enamels. To insure compatibility between the topcoat finish and the primer, both should be from the same manufacturer. For best results, follow the manufacturer's application instructions. Some finishes should not be applied to Overlaid plywood. These include automotive primers and enamels, lacquer undercoats and topcoats.

Edge Sealing
The most vulnerable portions of overlaid plywood are the edges. Because they absorb water which can lead to finish and surface deterioration, the edges require the most effective protection. Two coats of edge sealer must be applied for adequate protection against moisture penetration. Any conventional method of application may be used as long as adequate coverage is obtained.

For more information including the APA rating of MDO click here.