2914 Chapter 24 



panel axis, placed in a pressure vessel, submerged in water at 150°F, subjected 

 for 30 minutes to a vacuum of 15 inches of mercury, soaked at atmospheric 

 pressure for 30 minutes, and then removed and dried for 6 hours at 180°F in an 

 oven with forced air circulation; specimens are returned to the vacuum-soak 

 cycle and dried for 15 hours, completing two unbalanced cycles. These unbal- 

 anced cycles are repeated until six cycles are run. Total time required is 3 days. 

 Edges of each specimen are then probed with a blade-shaped square-ended tool 

 measuring 1/4-inch wide and 0.012 inch thick at the tip. If a separation is found 

 that is '/4-inch deep for one continuous inch, the specimen fails the test. 



Panels with exposure 2 durability rating are intended for protected construc- 

 tion uses where moderate delays in providing protection may be expected or 

 condiitons of high humidity and water leakage may exist. Composite and wood- 

 based panels so rated (not including those composed entirely of veneer) shall 

 satisfy the structural performance requirements described in the paragraph asso- 

 ciated with tables 24-3 and 24-4 (including criteria for fasteners) after being 

 wetted and redried as prescribed by American Plywood Association Test Meth- 

 od D-1. By this test method, specimens are submerged for 8 hours in water 

 maintained at 150°F, and then dried at 180° until they attain their original, as- 

 received, weight. 



Mold and bacteria resistance. — For details of these tests, readers are re- 

 ferred to American Plywood Association Test Methods D-2 and D-3. 



Dimensional tolerance and squareness of panels. — A size tolerance of 

 plus, 0, minus 1/8-inch is allowed on specified length and on specified width. A 

 thickness tolerance of plus or minus 1/32-inch is allowed on the trademark- 

 specified thickness. Panels shall be square within 1/64-inch per lineal foot 

 measured along the diagonals; all panels shall be manufactured so that a straight 

 line drawn from one corner to the adjacent comer is within 1/16-inch of the panel 

 edge. 



Moisture content. — Moisture content of panels at time of shipment shall not 

 exceed 18 percent of ovendry weight. 



PERFORMANCE STANDARDS FOR SHEATHING^ 



The American Plywood Association (1980) has also published a manufactur- 

 ing and performance standard for a wood-based panel intended for use as 

 sheathing for roofs, subfloors, and walls when fastened to supports spaced in 

 accordance with the span rating. The Association termed this product APA 

 RATED SHEATHING®; the panels can be all veneer, composite with veneer 

 faces and backs over wood particle cores, or all wood particles. 



These panels will withstand exposure expected in normal construction but 

 should not have an edge or surface permanently exposed to the weather; protec- 

 tion from the weather or long-term excessive humidity should be provided as 

 soon as possible. 



