How plaster mold volume calculations work
Mixing plaster for pottery molds requires achieving the correct consistency. Too much water yields a soft, porous mold that degrades quickly; too little water creates a dense mold that absorbs moisture too slowly during slip casting.
Standard mix ratios
- USG No. 1 Pottery Plaster standard ratio: 70 parts water to 100 parts plaster by weight (70:100).
- High-strength / dense molds: 65:100 ratio.
- Soft, absorbent press molds: 75:100 ratio.
Proper mixing technique
- Weigh out the required clean water into a clean bucket.
- Sift dry plaster powder slowly over the water surface. Allow it to soak undisturbed for 2 minutes.
- Mix thoroughly by hand or mixer paddle for 2–3 minutes without entraining air bubbles.
- Pour into mold box in a smooth, continuous stream.