Structural Flakeboards and Composites 29 1 3 



• APA Test Method P-3; 50- to 90-percent relative humidity. Speci- 

 mens are 3 inches wide and 41 inches long; these specimens are first 

 exposed to relative humidity of 50 percent until stable, and then to 90 

 percent. Linear expansion shall not exceed 0.30 percent of the length at 

 50 percent relative humidity along the major axis, or 0.35 percent 

 across the minor axis. Thickness swell shall be no more than 25 percent 

 of thickness at 50 percent relative humidity. This method corresponds 

 to ASTM D 1037 except for specimen size. 



• APA Test Method P-4; full-scale testing. Full-scale restrained-panel 

 linear expansion shall be not more than 0.20 percent along the major 

 axis and 0.25 percent across the minor axis. By this test method a 16- by 

 16-foot lumber frame with specified joist spacing is fabricated and 4- by 

 8-foot specimens are nail-assembled to it with end joints staggered 4 

 feet. On this frame, the major panel axis of each specimen runs perpen- 

 dicular to the joists. Overall dimensions of the assembly are measured 

 on the panelled surface at the ends and middle, both along and across 

 specimens' major panel axes. A continuous water spray is then applied 

 to the top surface with a garden sprinkler for 14 consecutive days. 

 Following wetting, the panel measurements are again taken. 



Stability. — Stability index is an indicator of ability to stay flat in service; as 

 measured by American Plywood Association Test Method P-5, it shall be 5.5 or 

 greater. By this test panel stiffness both along and across the major panel axis is 

 determined in dry panels; then linear expansion along and across the major panel 

 axis is measured from ovendry to vacuum-pressure-soak condition. The stability 

 index for each direction of each specimen is then calculated as: 



A = logio [tt^EI/L^cD] (24-1) 



where 



A = stability index 



EI = stiffness (Ib-in.^/ft) 



(I> = linear expansion (in. /in.) (Percent expansion divided by 100) 



L = span (in.) 



For the major panel axis, the span shall be the maximum span rating for which 

 the panel is being qualified. For the cross-panel direction, the span is the 

 maximum recommended interior nail spacing (generally 10 or 12 inches). 



Bond durability. — Panels shall be rated for exposure 1 or exposure 2. Panels 

 with exposure 1 durability rating are intended for protected construction uses 

 where durability to resist moisture due to long construction delays, or other 

 conditions of similar severity, is required. Composite and wood-based panels 

 (not including those composed entirely of veneer) so rated shall satisfy the 

 delamination requirements of American Plywood Association Test Method P-9 

 following moisture cycling according to their Test Method D-5. Under this test 

 regime, 1- by 5-inch specimens are cut with long dimension parallel to major 



