Plywood is an ideal material for concrete forming. It produces smooth concrete surfaces and can be used repeatedly - some overlaid panels up to 200 times or more. The thinner panels can be bent easily for curved forms and liners. Plywood's excellent stiffness minimizes deflection during pouring. Its natural insulating qualities help provide more consistent curing conditions. The large panel size and light weight reduce form construction and stripping time. And various surface textures are available for imparting attractive and unusual concrete textures.
Selecting and Specifying Concrete Panels
Virtually any Exterior-type APA panel can be used for concrete formwork because all such panels are manufactured with waterproof glue. Plyform, High Density Overlay (HDO) and certain proprietary Medium Density Overlay (MDO) panels are particularly well-suited to concrete forming use. During plywood production, these overlays are bonded to the plywood under heat and pressure in a press. The function of the overlay is to add stability, repel foreign substances from the surface and provide a smoother and more durable forming surface. The thermo-set resins used in overlay production are hard and resist water, chemicals and abrasion. HDO is most often specified where the smoothest possible concrete finish and maximum number of reuses is desired.
Depending on the needed strength of the panels, there are a variety of plywood grades to choose from including Plyform Class 1, Structural I Plyform, Plyform Class II, B-B Plyform, HDO Plyform and Medium Density. Additional grades specifically designed for concrete forming include special overlay panels and proprietary panels. These panels are designed to produce a smooth, uniform concrete service. Some proprietary panels are made of Group 1 wood species only, and have thicker face and back veneers than those normally used. These provide greater parallel-to-face grain strength and stiffness for the panel. Faces may be specially treated or coated with a release agent. Check with the manufacturer for design specifications and surface treatment recommendations.