Plasterboard (Drywall)

Sackett claims a wall covering of set gypsum sandwiched between sheets of paper — the plaster delivered as a dry, ready board. Note: the paper and the gypsum each do a job.

Cast a thin slab of plaster, let it set, and pick it up. It is rigid but brittle — it cracks and crumbles at the edges. Bare gypsum cannot be a board on its own.

Hold a sheet of heavy paper. It is tough and flexible but completely floppy — no stiffness at all. Paper alone is not a wall either.

Put down a sheet of paper, spread a thin even layer of wet gypsum on it, and lay a second sheet on top. Press flat. This sandwich is the board.

Let the gypsum set and pick the board up. Now it is stiff AND it holds together — the paper bandages the brittle core; the core stiffens the floppy paper. Together they are a wall.

Bend the finished board a little, then the bare gypsum, then the paper. The board is far tougher than the gypsum and far stiffer than the paper. The composite beats both parts.

Cut the paper on one face with a knife and snap the board along the line, then cut the back paper. It sizes in seconds with a knife — no saw, no dust cloud. This ease is half the invention.

Nail the board to two battens. It takes a nail without shattering (the paper holds the gypsum) and the wall is instantly up — dry, flat, finished.

Trowel wet plaster onto a lath of thin sticks and note it must dry for a long time before use. The board skips all of that. Time is the difference: minutes versus weeks.

Bring a flame to the board's face (outdoors, briefly). The paper chars but the gypsum core does not burn and stays cool — the fire-resistance that made it valuable. Note the difference from a bare wooden panel.

Set gypsum is calcium sulfate with water chemically locked inside it. In a fire that water is driven off as steam, which takes heat away and keeps the board's far side cool until the water is gone. Write down why that shields the studs behind.

Set two boards edge to edge and fill the seam with a little wet gypsum. Smoothed over, the joint disappears into one flat wall. That is how a room of boards becomes a seamless surface.

The patent. US 520,123, "Inside-wall covering", granted 22 May 1894 to Augustine Sackett of New York (filed 1890). Sackett was a Rensselaer-trained engineer, and his "Sackett Board" is the direct prototype of what the world now calls drywall, plasterboard, gypsum board or Sheetrock — used today in the great majority of new homes.

The invention is a composite, and the point is that neither material works alone. Set gypsum is rigid and fireproof but brittle — a bare slab crumbles at a touch (step 2). Heavy paper is tough but utterly floppy (step 3). Sandwich them and each cures the other's weakness: the paper acts as a continuous bandage and a nailing surface that stops the gypsum shattering, while the gypsum stiffens the paper into a rigid panel (steps 5 and 6). It is the same idea as reinforced concrete or plywood — a strong-but-brittle material carried by a tough-but-weak one — applied to the humblest surface in the building, the interior wall.

Why it changed how buildings go up. Traditional lath-and-plaster was a wet trade: skilled plasterers, multiple coats, and weeks of drying during which the building sat idle and could not be painted, wired-out or occupied. Sackett's board moved all of that curing into the factory, so the plaster arrives dry and finished; a wall goes up in minutes with a knife and nails (steps 7-9), by less-skilled labour, in any weather. That single change — from a wet, slow, skilled trade to a fast, dry, cuttable board — is a large part of why twentieth-century housing could be built quickly and cheaply enough to house a booming population.

The fire story is not a footnote. Gypsum is calcium sulfate dihydrate — it holds water in its crystal structure — so in a fire it releases that water as steam and stays cool, shielding the timber or steel behind it long enough for people to get out (steps 10-11). That is why building codes require gypsum board around structural members and between dwellings. The modest grey panel you nailed up in step 8 is, quietly, one of the most important fire-safety devices ever built into ordinary walls.