How drywall is made

Mine or capture gypsum

Raw gypsum is dug from quarries. Increasingly it is also recovered as a by-product, when coal power plants scrub sulfur from their smokestacks with limestone and produce so-called FGD gypsum.

Cook off the water

Raw gypsum, a calcium sulfate dihydrate, is heated to drive off its chemically bound water, then slightly rehydrated into the hemihydrate form known as plaster.

Mix the slurry

The plaster is blended with water, paper or glass fiber, a plasticizer, a foaming agent, ground gypsum crystals as an accelerator, and starch as a retarder. Additives can add mildew resistance or fire resistance.

Sandwich it in paper

The wet core is formed between two sheets of heavy paper or fiberglass mats on a moving line. Foaming leaves tiny pores that reduce weight.

Let the core set

The gypsum rehydrates and locks into a rigid mass while the board travels down the line.

Dry it in the chamber

Large drying chambers, typically gas-fired, drive off the excess water. Drying 1,000 square feet of wallboard takes between 1,750,000 and 2,490,000 BTU.

1,750,000–2,490,000 BTU per 1,000 sq ft

Cut and stack

The continuous board is cut into sheets, stacked and packaged for shipment. Up to 12% of drywall is wasted in manufacturing and installation, and some makers take scrap back to recycle.