Stucco and flour for the ceramic shell
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Flour and stucco together form the shell structure. The fine flour goes into the slurry and determines the detail and strength; the coarser stucco (sand) is sprinkled onto the wet layer after dipping and gives the shell grip and thickness. Here you will find both, in different materials and grit sizes for each layer of the process.
For the binder liquid, see binders.
Which material do you choose?
- ✓Fused silica — the standard choice for bronze and art casting. Low thermal expansion, which reduces shell cracking, and easy to knockout after casting. Available as flour (fine, for the slurry) and as sand (coarser, for the stucco).
- ✓Aluminum silicate (Clayrac, Remasil) — more economical and stronger. Our standard and cheapest stucco, and the shell is easy to remove with it. Very suitable for art casting.
- ✓Zircon — very fine material for an extremely detailed and strong contact layer. Ideal for high surface demands or higher casting temperatures. Note: less porous, so use carefully to prevent cracking.
Grain size per layer
A common build-up with fused silica stucco:
→RG1 (50/100 mesh) — the first or first two layers (contact layer).
→RG2 (30/50 mesh) — the subsequent three layers.
→RG3 (10/30 mesh) — the remaining back-up layers.
For flour: finer flour (e.g., 200 or 325 mesh) provides more detail. The periodically mixed slurries based on xanthan or Shellspen deliberately use fine 325 mesh flour.
⚠️ Safety: wear a dust mask when handling sand, flour, and stucco. Most sands contain cristobalite, which can be harmful if inhaled long-term. Also wear safety glasses.