PLYWOOD
PLYWOOD WAS THE FIRST TYPE OF ENGINEERED WOOD TO BE INVENTED. IT IS MADE FROM THIN SHEETS OF WOOD VENEER, CALLED PLIES OR VENEERS, WHICH ARE STACKED TOGETHER WITH THE DIRECTION OF EACH PLY'S GRAIN DIFFERING FROM ITS NEIGHBORS' BY 90° (CROSS-BANDING). THE PLIES ARE BONDED UNDER HEAT AND PRESSURE WITH STRONG ADHESIVES, MAKING PLYWOOD A TYPE OF COMPOSITE MATERIAL. A COMMON REASON FOR USING PLYWOOD INSTEAD OF PLAIN WOOD IS ITS RESISTANCE TO CRACKING, SHRINKAGE, TWISTING/WARPING, AND ITS GENERAL HIGH DEGREE OF STRENGTH.
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PLYWOOD PRODUCTION REQUIRES A GOOD LOG, CALLED A PEELER, GENERALLY STRAIGHTER AND LARGER IN DIAMETER THAN THAT REQUIRED FOR PROCESSING BY A SAWMILL. THE LOG IS PEELED INTO SHEETS OF VENEER WHICH ARE THEN CUT TO THE DESIRED DIMENSIONS, DRIED, PATCHED AND GLUED TOGETHER TO FORM THE PLYWOOD PANEL. THE PANEL CAN THEN BE PATCHED, RESIZED, SANDED OR OTHERWISE REFINISHED, DEPENDING ON THE MARKET IT WAS INTENDED TO BE SOLD IN.
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A VAST NUMBER OF VARIETIES OF PLYWOOD EXIST, ALL MANNER OF CONDITIONS AND USES. SOFTWOOD PLYWOOD IS USUALLY MADE EITHER OF DOUGLAS FIR OR SPRUCE, AND IS TYPICALLY USED FOR CONSTRUCTION AND INDUSTRIAL PURPOSES. DECORATIVE PLYWOOD IS USUALLY FACED WITH HARDWOOD, INCLUDING RED OAK.
PLYWOOD MEANT FOR INDOOR USE GENERALLY USES THE LESS EXPENSIVE GLUE (WHICH HAS LIMITED WATER RESISTANCE), WHILE OUTDOOR AND MARINE GRADE PLYWOOD ARE DESIGNED TO WITHSTAND ROT AND USE A WATER-RESISTANT GLUE TO PREVENT DELAMINATING AND TO RETAIN STRENGTH IN HIGH HUMIDITY.
THE MOST COMMON VARIETIES OF SOFTWOOD PLYWOOD COMES IN THREE, FIVE OR SEVEN PLIES). PLIES VARY IN THICKNESS DEPENDING ON THE PANEL THICKNESS. ROOFING CAN USE THE THINNER 3/8-INCH PLYWOOD. FLOORBOARDS ARE AT LEAST 5/8-INCH DEPENDING ON THE DISTANCE BETWEEN FLOOR JOISTS. PLYWOOD IS OFTEN TONGUE AND GROOVED FOR FLOORING APPLICATIONS. TWO OF THE EDGES WILL HAVE "GROOVES" NOTCHED INTO THEM TO FIT WITH THE ADJACENT "TONGUE" THAT PROTRUDES FROM THE NEXT BOARD.
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SOFT WOODS:
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