Short answer
Settling is physical separation of the pigment dispersion. Heavy inorganic pigments settle fastest. Soft sediment can be re-dispersed by thorough mixing, but a hard cake means the dispersion has changed and the batch should not be used for colour-critical work. Rotate stock first-in first-out, agitate before use and never thin the colorant to loosen it.
Likely causes
Long storage without agitation
Dense pigments such as titanium dioxide and iron oxides sink over months.
Temperature cycling
Freezing or prolonged heat can destabilise the dispersion and promote flocculation.
Contamination
Water, an incompatible polyol or thinner, or a container left open and skinning.
Age
Stock held beyond its stated shelf life (12 months sealed for Chemie PU colorants).
How to diagnose it
- Probe to the bottom with a clean spatula: soft sediment or hard cake?
- Compare the batch age against shelf life.
- After remixing, check fineness of grind with a grind gauge and make a drawdown against the standard.
How to fix it
- Soft sediment: roll the drum or mix with a low-shear stirrer until uniform, then verify against the standard.
- Hard cake: do not use for colour-critical parts. Quote the batch number to your supplier.
- Do not dilute with solvent or polyol to loosen settled colorant.
How to stop it coming back
- First-in, first-out stock rotation.
- Store sealed, cool and dry, away from freezing and direct heat.
- Use recirculation on day tanks and smaller packs for slow-moving shades.
Where this problem appears most
Send us your batch number, PU system and a photo of the defect and our technical team will help you trace the cause. Ask a technical question.
