When the appropriate sections of Veneer are assembled for a particular run of plywood, the process of laying up and gluing the pieces together begins. This may be done manually or semi-automatically with machines. In the simplest case of three-ply sheets, the back veneer is laid flat and is run through a glue spreader, which applies a layer of glue to the upper surface. The short sections of core veneer are then laid crossways on top of the glued back, and the whole sheet is run through the glue spreader a second time. Finally, the face veneer is laid on top of the glued core, and the sheet is stacked with other sheets waiting to go into the press.
The glued sheets are loaded into a multiple-opening hot press. presses can handle 20-40 sheets at a time, with each sheet loaded in a separate slot. When all the sheets are loaded, the press squeezes them together under a pressure of about 110-200 psi (7.6-13.8 bar), while at the same time heating them to a temperature of about 230-315° F (109.9-157.2° C). The pressure assures good contact between the layers of veneer, and the heat causes the glue to cure properly for maximum strength. After a period of 2-7 minutes, the press is opened and the sheets are unloaded.
The rough sheets then pass through a set of saws, which trim them to their final width and length. Higher grade sheets pass through a set of 4 ft (1.2 m) wide belt sanders, which sand both the face and back. Intermediate grade sheets are manually spot sanded to clean up rough areas. Some sheets are run through a set of circular saw blades, which cut shallow grooves in the face to give the plywood a textured appearance. After a final inspection, any remaining defects are repaired.
The finished sheets are stamped with a grade-trademark that gives the buyer information about the exposure rating, grade, mill number, and other factors. Sheets of the same grade-trademark are strapped together in stacks and moved to the warehouse to await shipment.