USG Closes Southard Gypsum Plant Raising Costs for Specialty Plasters
USG will idle its Southard plant, tightening the supply of high-purity specialty gypsum and raising plaster sourcing costs.
Plaster Manufacturing
Hydration Chemistry
Calcination of gypsum rock at temperatures ranging from 120 to 180 degrees Celsius produces hemihydrate calcium sulfate. Plaster manufacturing involves the subsequent grinding of this hemihydrate into a fine powder that sets upon the addition of water. This powder undergoes recrystallization to reform into solid dihydrate gypsum crystals.
Production Logic
Industrial kilns regulate thermal exposure to prevent the conversion of hemihydrate into anhydrous calcium sulfate, which loses the ability to rehydrate efficiently. Precise moisture control within the kiln environment prevents the formation of dead-burned plaster that remains chemically inert. Rotary or kettle dryers facilitate the uniform distribution of heat across the gypsum feedstock to ensure batch consistency.
Mechanical pulverizers then reduce the calcined material to a specific surface area particle distribution that dictates the setting time of the final product. Additives modulate these reaction kinetics to compensate for variations in raw material purity or ambient humidity.
Market Variability
Construction demand fluctuates based on regional housing starts and the availability of synthetic byproduct gypsum from industrial flue gas desulfurization processes. Manufacturers balance the lower cost of synthetic material against the consistent mineralogical properties found in mined natural gypsum deposits. Price stability depends on the proximity of processing plants to extraction sites or coal-fired power stations to minimize transport expenditure.
Energy costs represent the primary variable expense because the dehydration of gypsum requires high thermal inputs that dictate the margin between raw feedstock and finished commodity. The industry relies on the predictable relationship between the calcination temperature and the resulting physical strength of the hardened wallboard or coating.