Sharp grains on the casting surface
Indicates that the metal managed to slightly penetrate the primary shell coat in some areas
Causes of this defect are evident in the shell portion of the process; to cure, R&R recommends taking the following actions:
Primary stucco touched or hit the wax due to low viscosity of the primary binder or slurry.
Check on slurry viscosity to ensure it is in normal operating parameters.
Excess draining is creating too thin of a slurry layer and allowing stucco to touch the wax.
When the stucco touches the wax, it typically traps air against the surface; which results in a defect.
The fall height of the stucco is too far from the tree (rainfall or barrel rain sander only).
Adjust the position of the tree in the rain sander to reduce the distance from the source.
The stucco is too coarse.
Use a finer stucco on the initial shell coat.
Primary slurry is too thin.
Increase slurry viscosity.