Do pre-dispersions settle, and how do I keep batches consistent?

They settle, because the particles are denser than the carrier. That is physics; the job is to keep it redispersible and to dose by solids.

How fast depends on three things: particle size, since agglomerates settle quickly; carrier viscosity, since thicker settles more slowly; and storage temperature, since heat thins the carrier and speeds it up. A well-dispersed nano grade settles slowly into a loose layer that stirs back in. A flocculated one settles into a hard cake.

Store cool, avoid heat and freeze-thaw, use first in first out, and stir with a paddle rather than shaking. Confirm by sampling top, middle and bottom for solids content before the batch is charged.

Consistency comes from three habits: verify the drum is homogeneous before weighing; dose by effective filter solids rather than by dispersion weight; and retain a standard sample for colour and fineness comparison.

If the drum has hard lumps that survive stirring, the flocculation is irreversible. Do not use it — the consequence is lower protection and more white cast, and it will not show up until the batch is finished.