3020 Chapter 24 



24-15 WEATHERING DURABILITY 



There is some doubt concerning the suitability of phenolic-bonded flakeboard 

 for long-term exterior applications in which panels are fully exposed to the 

 weather. Efforts to protect structural flakeboard from the effects of weathering 

 might be more promising than attempts to greatly improve its resistance. 



Jokerst (1968) found that 8-year exposure of Douglas-fir {Pseudotsuga men- 

 ziesii (Mirb.) Franco) flakeboard (7-3/16- by 13-inch specimens) on an exterior 

 test fence is more severe than six cycles of the ASTM D 1037-72 accelerated 

 aging exposure (American Society for Testing and Materials 1975a). This test 

 requires that the specimens complete six cycles of accelerated aging. Each cycle 

 consists of the following: (1) Immersing specimens in water at 120°F for 1 hour; 

 (2) spraying with steam and water vapor at 200°F for 3 hours; (3) freezing by 

 storing at 10°F for 20 hours; (4) heating at 210°F in dry air for 3 hours; (5) 

 spraying again with steam and water vapor at 200°F for 3 hours; and (6) heating 

 in dry air at 210°F for 1 8 hours. Execution of the six cycles requires 3 to 4 weeks. 



Some of Jokerst 's other conclusions were: 



• Phenolic-bonded flakeboards far out-performed urea-bonded boards. 



• Much of the deterioration of the flakeboards occurred in the first year; 

 deterioration continued at a lesser rate throughout the exposure period. 



• The primary causes of deterioration of the flakeboard were springback 

 from compression set, deterioration of the binder, and differential 

 shrinkage of adjacent particles during moisture changes. 



• A well-maintained coat of paint on the flakeboards in the test-fence 

 exposure greatly improved durability. 



Meierhofer and Sell (1977) found that treating edges and surfaces of particle- 

 board with water repellent and then painting with an alkyd, epoxide, or polyure- 

 thane resin effectively improved weathering performance. 



There are no data published on the effect of exposure-fence weathering of 

 phenolic-bonded flakeboard made from mixed southern hardwoods. Price'" is 

 evaluating performance of such flakeboard during 5 years of unprotected expo- 

 sure in Louisiana (fig. 24-47). This flakeboard was fabricated according to the 

 procedure advocated by Hse et al. (1975), and results should be published by 

 1985. It is likely that MOE, MOR, and IB of the boards will all be very 

 significantly reduced; because of increase in panel thickness, however, panel 

 stiffness (EI) and capacity to carry loads in bending will be less affected. Figure 

 24-47 (bottom) gives some idea of panel appearance nfter 3 years of exposure. 



Carrol (1980) noted that in North America flakeboard has a solid history of 

 successful use as sheathing and cladding in general building construction, but 

 there is no general agreement on test procedures appropriate for its accelerated 

 aging or weathering. Readers needing to compare test procedures should find 

 useful overviews by Carrol (1980) and River et al. (1981). 



