The terms a plant engineer actually uses.

Definitions aligned to the published standards that govern this industry — ASTM C11 for terminology, EN 520 for board classifications, ASTM C472 for test methods, and Wirsching's chapter in Ullmann's Encyclopedia for chemistry. Full references at the foot of the page.

BNS

β-Naphthalene sulfonate formaldehyde polycondensate. Anionic dispersant historically used in gypsum slurries; disperses stucco particles via electrostatic repulsion.

Bound water

The structural water in gypsum. CaSO₄·2H₂O contains 2 mol H₂O per mol, i.e. 20.9 wt% of the crystal; only released on calcination above ~100 °C.

bwoc / bwos

By weight of cement / by weight of stucco. Standard dosage convention: dosage in grams of admixture per 100 g of the reference solid.

Calcination

Thermal dehydration of gypsum. CaSO₄·2H₂O → CaSO₄·½H₂O (β-hemihydrate) below ~180 °C in kettles or flash calciners; further heating yields soluble and then insoluble anhydrite.

DensGlass

Georgia-Pacific trade name for a family of glass-mat faced (paperless) gypsum sheathing boards.

Dihydrate

Calcium sulfate dihydrate, CaSO₄·2H₂O. The mineral gypsum and the final set form of a plasterboard core.

Edge dam

The moving side rails / edge former at the wet end of the board machine that constrain the slurry between the two paper webs to the specified board width.

FGD gypsum

Synthetic gypsum recovered from flue-gas desulfurization at coal-fired power stations. Chemically equivalent to natural dihydrate and widely used as raw material for plasterboard.

Hemihydrate

Calcium sulfate hemihydrate, CaSO₄·½H₂O. Two forms: α-hemihydrate (autoclaved, higher density) and β-hemihydrate (kettle/flash calcined, the standard plasterboard stucco).

Lignosulfonate

Water-soluble byproduct of sulfite pulping of wood. Used at low cost as a plasticiser/dispersant; carries residual sugars that can act as set retarders.

PCE

Polycarboxylate ether. Comb-shaped copolymer with an anionic backbone and polyether side chains; disperses stucco predominantly by steric hindrance.

PMHS

Poly(methylhydrogensiloxane). Reactive silicone used to produce hydrophobic (water-repellent) gypsum boards; releases hydrogen when the Si–H bond reacts on the crystal surface.

Set time

Time from end of mixing to a defined penetration resistance of the paste. Measured for gypsum by the Vicat needle apparatus per ASTM C472; usually reported as initial and final set.

STMP

Sodium trimetaphosphate, Na₃P₃O₉. Cross-links pre-gelatinised starches within the gypsum core to increase bond strength between core and paper.

Stucco

Industry name for calcined gypsum used to make plasterboard: mostly β-hemihydrate with small amounts of soluble anhydrite and residual dihydrate.

Type H / Type F / Type I

EN 520 letter classes for plasterboards with defined properties: H — reduced water absorption, F — improved core cohesion at high temperature, I — increased surface hardness (among others).

Type X

Fire-resistance-rated gypsum board classified per ASTM C1396/C1396M. Cores contain additives such as glass fibre and vermiculite that maintain integrity under standard fire exposure.

Vicat apparatus

Standard needle penetration apparatus used to determine setting times of hydraulic binders and gypsum plasters (EN 196-3; ASTM C472 adaptation for gypsum).

W/S ratio

Mass ratio of gauging water to dry stucco fed to the mixer. Determines slurry rheology, void fraction after set, and the excess water the kiln must evaporate.