Concrete Forming Design and Construction

High Density Overlay (HDO) Plyform

High Density Overlay (HDO) Plyform concrete forming panelsThis Plyform panel meets the same general specifications as Plyform Structural I or Class I. All classes of HDO Plyform have a hard, semi-opaque surface of thermosetting phenolic resin-impregnated material that forms a durable, continuous bond with the plywood. During plywood production, these overlays are bonded to the plywood under high 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 thermosetting phenolic resins used in overlay production are hard and resist moisture, chemicals and abrasion. HDO is most often specified where the smoothest possible concrete finish and maximum number of reuses is desired.

The abrasion-resistant surface should be treated with a release agent prior to its first use and between each pour to preserve the surface and facilitate easy stripping. HDO Plyform is most often specified when the smoothest possible concrete finishes are desired, because the panel has a hard, smooth surface. It can impart a nearly polished concrete surface. Both sides of HDO are moisture resistant but cannot always be used to form concrete with equal effectiveness unless specifically made for that purpose. Scratches and dents in the backs caused by fastening the panels to the supports may make the use of both sides impractical.

Various grades of HDO Plyform may be available; check with your supplier. With reasonable care, HDO Plyform will normally produce 20 to 50 reuses or more. Some concrete-forming specialists achieve 200 or more reuses with good results.