A. Paul Fisette, director of the Building Materials and Wood Technology program at the University of Massachusetts in Amherst, responds: OSB is usually bonded with phenol formaldehyde in conformance with the ANSI A208 standard (1-1989, Grade 2-M-W). This resin reacts to become insoluble, resulting in negligible or no offgassing. The miniscule amounts of formaldehyde will dissipate in time.
There’s an alternate binder used by some OSB manufacturers that contains no formaldehyde. It’s a type of urethane known as MDI (methane di-isocyanate). OSB made with MDI is more moisture-resistant and dimensionally stable, but it’s also more expensive. It’s mainly used in brand-name T&G subfloor products, where any swelling from moisture...
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