Slip Casting

Slip Casting Cycle Calculator

Estimate casting time, drain time, demold window, and mold drying time for plaster slip casting.

Reviewed by ClayCalc Editorial · Updated

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Enter your measurements above and click Calculate.

How Slip Casting Works

Slip casting uses the porosity of plaster molds to extract water from liquid clay slip, building up a wall of uniform thickness against the mold surface. The longer the slip sits in the mold, the thicker the wall. Timing is critical — too short and the piece collapses on demolding; too long and the piece cracks as the clay begins to shrink away from the plaster.

Factors Affecting Casting Rate

Faster Casting

  • New, dry plaster mold
  • Higher slip SG (more solids)
  • Pottery plaster (more porous than Hydrostone)
  • Warmer casting environment

Slower Casting

  • Old or saturated mold
  • Lower slip SG (more water)
  • Hydrostone mold (denser)
  • Cold workshop

Mold Care and Longevity

Allow molds to fully dry between casts — typically 24 hours minimum. Stack molds open-face up in a warm, ventilated area. Never dry molds in a hot kiln; high heat destroys the plaster's crystal structure. A well-maintained pottery plaster mold lasts approximately 100 casts before absorptivity drops significantly.

Method & review note

About this calculation

Uses weight, volume and ratio relationships. Product data sheets and measured viscosity/thixotropy take priority over generic presets.

Reference: USG — No. 1 Pottery Plaster. See the editorial methodology for testing, precision and corrections.

Input handling: Values are sent to the ClayCalc server for this request and are not written to the application database.

Read the Pottery Plaster Mixing

Frequently Asked Questions

How do I know when the wall is thick enough to drain? expand_more
Observe the slip level dropping — casting stops when the meniscus stops receding. For production work, cut test tiles to verify wall thickness, then time your future pours consistently.
How many casts does a plaster mold last? expand_more
A well-made Pottery Plaster #1 mold typically lasts 50–100 casts before it loses sufficient absorbency. Hydrostone molds can last 150–200+ casts. Store molds dry and avoid contamination with water or soap.
Why must molds dry between casts? expand_more
Plaster can only absorb water when its pores are empty. A saturated mold will not draw water from the slip — the casting process stops. Allow 24 hours minimum drying between casts (or use a drying cabinet with warm air).