For decades we have used gypsum sheathing in commercial construction. Standard gypsum sheathing can be traced back to pre-World War II. In the 1940s, water-repellant face paper was added to give a good product more value. The sheathing would come in square or tongue-and-groove ends for a snug fit. Gypsum sheathing saw the next improvement when the gypsum core could be blended with a petroleum-based product, thus making it water resistant through and through. The ATSM that covered the manufacturer of this product was C-79 and has since been replaced by C-1396.
But times continue to change and our industry has a history of stepping up to meet challenges. Mold and mildew became a problem that no one was able to completely escape. While the gypsum core of the sheathing does not readily support the growth of mold, the face paper can. The invention of fiberglass-faced gypsum sheathing was developed to solve that problem. It took a little time to catch on, but when it did, it seems we never looked back. This new sheathing was more than just a new facing material—it also has a silicone infused gypsum core. The new sheathing could be left exposed to inclement weather for several weeks longer than anyone had previously thought possible. This created a need for new ATSM, and so ATSM C-1178 was developed.