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In the applications for which they are manufactured, the two products are virtually interchangeable. Although different in composition and appearance, plywood and OSB are manufactured according to the same performance standard criteria. Which product you choose will depend on your requirements for a variety of characteristics including finished size, surface quality and panel density.
Overlaid plywood panels are available with some type of face enhancement. Two common face coverings are a Medium Density Overlay (MDO) or High Density Overlay (HDO), which are resin-impregnated fiber surfaces bonded to one or both panel faces under heat and pressure. Other types of enhanced surfaces include fiberglass-reinforced plastic, polyethylene (HDPE), hardboard, metal and other materials for exceptionally smooth or special-use surfaces. The APA Product Guide: HDO/MDO Plywood, Form B360, describes HDO and MDO plywood applications, properties and characteristics, plus shop practice and finishing recommendations.
Sanded plywood panels are structural panels with face and back plies that are sanded smooth in the manufacturing process.
Touch-sanded panels are plywood panels “sized” to uniform thickness by light surface sanding during manufacture. Sander skips are admissible.
A ply is single veneer in a panel. In plywood, a layer consists of one or more adjacent plies having the wood grain in the same direction. For instance, four-ply panels always have three layers with both core plies at right angles to the faces. The two core plies are one layer and each face is a layer. In OSB panels, the reconstituted wood portion is one layer and each face is a layer.
The term Structural I refers to certain specialized strength and stiffness characteristics of plywood and OSB panels. The term Exposure 1 refers to the glue bond durability of a plywood or OSB panel.
Exterior panels are suitable for applications subject to long-term exposure to weather or moisture.
Exposure 1 panels may be used for applications where construction delays may be expected prior to providing protection. Exposure 1 panels are made with the same exterior adhesives used in Exterior panels. However, because other compositional factors may affect bond performance, only Exterior panels should be used for long-term exposure to weather.
Note: APA Rated Plywood Sheathing Exposure 1, commonly called “CDX” in the trade, is sometimes mistaken as an Exterior plywood panel and incorrectly used in applications for which it does not possess the required resistance to weather. “CDX” is manufactured with a C grade veneer on the face and a D grade veneer on the back. D grade veneers are not suitable for Exterior applications and should only be used for applications as outlined under Exposure 1 above. For sheathing grade panels that will be exposed long-term to weather, specify APA Rated Sheathing Exterior (C-C Exterior plywood under PS 1).
For more information, please refer to Technical Topics: Bond Classification, Form TT-009, available as a free PDF from the APA Publications Library.