2910 Chapter 24 



Table 24-2. — Property requirements for waferboard and flakeboard bonded with 



phenol-formaldehyde resins or equivalent bonding systems 



(National Particleboard Association 1980) 



Property Waferboard Flakeboard 



Grade 2-MW 2-MF 



Length and width tolerance (inch) +0 to - 1/8 +0 to - 1/8 



Thickness tolerance, unsanded (inch) 



Panel average' ±0.030 ±0.030 



Within-panel^ ±0.030 ± 0.030 



Thickness tolerance, sanded (inch) 



Panel average' ±0.015 ±0.015 



Within panel^ ±0.010 ±0.010 



Modulus of rupture (psi)^ 2,500 3,000 



Modulus of elasticity (psi)^ 450,000 500,000 



Internal bond strength (psi)^ 50 50 



Hardness (pounds)^ 500 500 



Linear expansion between 50- and 



90-percent relative humidity 0.20 0.20 

 (percent)^ 



'Panel average from nominal. 

 ^Individual measurement from panel average. 



^Five-panel average; the five-panel sample shall not contain any individual panel having this 

 property more than 20 percent below the value tabulated. 



From these criteria, the American Plywood Association (1980) published a 

 manufacturing and performance standard for a wood-based structural panel 

 intended for use as combination subfloor and underlayment when fastened to 

 supports as specified. They termed the product APA RATED STURD-I- 

 FLOOR® panels; the panels can be all veneer, composite with veneer faces and 

 backs over wood particle cores, or all wood particles. Performance standards for 

 this product follow. 



Application. — The panels will withstand exposure expected in normal con- 

 struction, but should not have an edge or surface permanently exposed to the 

 weather. The major panel axis (generally the long dimension) is placed across 

 supports spaced no further apart than the span rating, i.e., for composite or all 

 particle panels the distances between centers of supports may be specified as 16, 

 20, or 24 inches. (Criteria for 48-inch span are underdevelopment.) Panels must 

 be continuous over two or more spans. When applying thin resilient finish 

 flooring, a layer of underlayment is recommended for panels without a veneer 

 face. If underlayment is not used, nails should be set 1/16-inch deep (1/8-inch 

 for 1-1/8-inch panels), but nail holes should not be filled. Edge joints should be 

 filled and any surface roughness should be thoroughly sanded. 



Fastening. — Nail-fastened floors should use 6d deformed- shank nails for 

 panels 3/4-inch thick or less, and 8d deformed-shank nails for thicknesses of 7/8- 

 inch through 1-1/8 inches. For 1-1/8-inch panels, lOd common nails may be 

 used if supports are well seasoned. Nails should be drive 6 inches apart at panel 

 edges and 10 inches apart at intermediate supports. 



