Arcosa Pottery Plaster

Pottery plaster for slip-casting molds, press molds, hump and slump molds, and throwing bats. Arcosa Pottery Plaster is made by Arcosa Specialty Materials in Oklahoma. It replaces USG No. 1 Pottery Plaster, which USG stopped making in 2026. Read why we switched and how the two compare. If you used USG No. 1 Mix it the same way: 70 parts water to 100 parts plaster, by weight. On paper it is very close. Strength is about the same (2,500 psi vs 2,400 psi for No. 1). It expands slightly more as it sets (0.28% vs 0.21%). Neither maker publishes a number for absorption. Test before you remake a production mold. Pour a test mold, cast in it, and compare wall thickness and release against your old molds. A 1 lb bag is enough for a test block; use 5 or 10 lb for a small cup mold. Don't combine plasters within one mold set. If the pieces of a multi-part mold have to fit together and absorb evenly, pour every piece from the same plaster. We're testing Arcosa against our remaining USG No. 1 in our own shop, and we'll post the results on the blog. Typical properties (manufacturer's data) Water to plaster 67–70 parts water per 100 parts plaster, by weight Set time 27–37 minutes Compressive strength 2,500 psi Maximum setting expansion 0.28% Fineness 98.5–100% passes 100 mesh Color White Arcosa Pottery Plaster data sheet (PDF) How much water Plaster Water (70:100) 1 lb 0.7 lb (11 fl oz / 320 g) 5 lb 3.5 lb (about 1.6 L) 10 lb 7 lb (about 3.2 L / 0.84 gal) 25 lb 17.5 lb (about 7.9 L / 2.1 gal) 50 lb 35 lb (about 15.9 L / 4.2 gal) Weigh the water, then sift the plaster in slowly and evenly. Let it soak 2–4 minutes without stirring, then mix for 2–5 minutes. Warmer water and longer mixing make it set faster. Step-by-step: Instructions for Mixing Plaster. Sizes 1 lb, 5 lb, 10 lb, 25 lb and 50 lb bags. Buying a pallet or more? Call us at 888-915-1196. Safety Plaster dust irritates eyes, skin, nose and throat. Wear a dust mask or respirator when sifting, and gloves if your skin is sensitive. Never pour plaster or plaster rinse water down a drain: it sets in the pipe. Let leftover plaster harden in the bucket and throw it in the trash.