Paint viscosity: when to use a Stormer KU measurement

If a paint specification calls for a KU result, start by confirming its Stormer test procedure. The unit is part of the requirement, not simply a display preference. A supplier quoting viscosity in mPa·s may be describing a different test, even when both reports concern the same coating.

Identify the question the test must answer

ASTM D562 covers paint and related coating consistency evaluated in Krebs Units using a Stormer-type viscometer. Its stated use includes specifying and controlling paint consistency. The public description establishes the method's scope; the complete standard is needed for the procedure. [1]

For a Measight application inquiry, attach the customer's method or the relevant specification line. Identify whether the result is used for incoming inspection, a production adjustment or final batch release. This helps keep the equipment discussion tied to the actual acceptance requirement.

Review the STM catalog configuration

The current STM-2 and STM-2T entries both list a 40.2–141.0 KU range, 200 ±1 rpm rotational speed and a 500 mL container capacity. Those are useful starting parameters for a shortlist.

They do not, by themselves, establish standard conformity or explain every difference between the models. Request the supplied measuring paddle, container requirements, verification documents, operating procedure and any display or workflow differences you need to compare. Also distinguish the stated container capacity from the fill quantity required by the applicable method.

Keep rotational results in their own context

ASTM D2196 addresses rotational-viscometer characterization of non-Newtonian materials. Its public description includes apparent viscosity and investigations of shear-dependent or time-dependent behavior. It serves a different measurement purpose from treating every coating as one KU value. [2]

If your laboratory needs a rotational method as well as a Stormer check, record them as separate tests. For example, a proposed SNB-2 setup should carry its own spindle, speed, temperature and acceptance criteria. Do not overwrite the original KU field with a value from another method simply because both instruments report a form of viscosity or consistency.

Make the coating inquiry specific

Our suggested brief includes the following:

• Coating description and the stage at which a sample is taken.
• Required method, reporting unit and expected acceptance interval.
• Test temperature and available sample quantity.
• Current instrument configuration, if a replacement is being considered.
• Documentation and verification requirements for the purchasing team.

For example, ask for a review of an attached KU procedure against STM-2 and STM-2T, with missing configuration details identified. That gives the quotation a checkable basis. If the wider aim is to understand application behavior, explain that separately so the proposed testing plan can address it rather than assuming that one consistency result answers every formulation question.