I think A too much water in the stone for the cast....
too much water will decrease the setting expansion of the model, so in a kind of contracted model you will produce a casting that will not fit the mouth...
hi it,s B gypsum materials expand during setting,
primarily because the dihydrate crystals push against each other
as they form. Several factors can be altered to affect setting
expansion.
1. Mixing Time: Increasing the mixing time, within
practical limits, increases expansion by increase the number of
nuclei of crystallization of dihydrate particles.
2. W/P Ratio: Decreasing the W/P ratio increases expansion
by also increasing the number of nuclei of crystallization of
dihydrate particles.
3. Accelerators and ******ers: Accelerators and ******ers
not only affect setting time, but also affect expansion of the
gypsum. Both decrease expansion by changing the shape of the
developing dihydrate crystals.
Summary of factors that influence setting time and expansion of
the gypsum materials:
*Increasing the mixing time or decreasing the W/P ratio
shortens the setting time and increases expansion by creating
more nuclei of crystallization of calcium sulfate dihydrate per
unit volume. They also increase strength by producing a more
dense product