Table 12 . - Structural flakeboard requirements contained in United States and Canadian 



standards (minimum average values) 



Requirements 



U.S.A. 



Canada 



Standard 

 Type 



Density (lb/ft 3 ) 



Thickness tolerance (+ in) 

 Modulus of rupture (lb/in 2 ) 

 Modulus of elasticity (lb/in 2 ) 

 Interna 1 bond (lb/in 2 ) 

 Linear expansion (percent) 



(maximum average 50%-90% RH) 

 Screw-holding strength (lb) 



Face 



Edge 



Residual bending strength after 

 accelerated aging (percent of 

 initial) 



CS 236-66 

 2-B-2 

 37 to 50 



0.016 

 2,500 

 450,000 

 60 



0.25 



250 

 200 

 50 



CSA 0188-1975 

 Grade P S Q 

 Not specified or 

 not applicable 

 0.030 - 0.015 

 2,000 

 400,000 

 40 

 0.25 



Not specified 

 Not specified 

 50 



considered suitable for roof and wall sheathing in the U.S. (HUD-FHA 1975). The U.S. 

 standard (U.S. Department of Commerce 1966) does not specify end use for such boards, 

 but the National Particleboard Association (1970) has obtained recognition of such 

 properties for these panels to be used as decking (subf loor-underlayment combination) 

 in mobile homes and factory-built housing. One U.S. manufacturer has obtained recogni- 

 tion of his product by the International Conference of Building Officials (ICBO 1972) 

 as a satisfactory alternative material to that specified in the Uniform Building Code 

 for roof, wall, and floor sheathing and underlayment . Hence, cities and States using 

 the Uniform Building Code would allow use of this board in buildings. The Canadian 

 and U.S. National Particleboard Association standards currently specifying physical 

 property levels for structural flakeboards are shown in table 12. To guide the Forest 

 Service Program, service load severity and panel properties (table 13) were established. 

 A single structural flakeboard having an average MOE (modulus of elasticity) of 725,000 

 to 800,000 psi and near-minimum MOR (modulus of rupture) of 4,500 psi could meet load 

 carrying requirements for equivalent thicknesses of plywood: the use of 5/8- to 3/4-inch 

 single layer floor and 1/2-inch plywood roof sheathing is common (Countryman 1975) . 



Board Configurations 



Defining the physical properties in structural panels poses the problem of select- 

 ing board configurations to meet requirements at reasonable or competitive cost. The 

 Canadians have had excellent success with a panel composed of randomly oriented flakes, 

 either placing the best quality flakes on the surface of the panel and mixed quality 

 flakes in the core (three-layer random board) or simply randomly distributing mixed 

 quality flakes throughout (homogeneous random board) . Emplacing the highest quality 

 flakes on the panel surfaces improves bending strength and stiffness. Further control 

 of processing steps--controlling closure rate and pressure to densify surfaces, using 

 minimum resin to attain desired strength, selecting the proper proportion of surface 

 flakes to core material--improves random three-layer structural flakeboard panels 

 (Ramaker and Lehmann 1976; Geimer and others 1975b) . 



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