Organoclay for Epoxy Zinc-Rich Primers: Balancing Anti-Settling and Redispersibility

Epoxy zinc-rich primers present a demanding challenge for rheology control. Their high zinc loading supports corrosion protection, but also makes pigment suspension difficult during storage.

For coating manufacturers, the practical problem extends beyond visible settling. A primer may develop a compact sediment that is difficult to remix, while another formulation may resist settling but become too viscous for efficient application.

The formulation target is therefore a balance: sufficient structure at rest, manageable flow during mixing and spraying, and reliable redispersibility after storage.

Why Zinc-Rich Primers Need Effective Suspension Control
Zinc dust has a much higher density than the surrounding resin and solvent phase. During storage, this density difference creates a strong tendency for particles to settle. BYK’s technical guidance specifically identifies organoclay as an option for preventing settling in solvent-borne zinc-containing systems.

However, the rate and character of sedimentation depend on the complete formulation:
Zinc particle size distribution and morphology.
Zinc loading and the balance between pigment and binder.
Resin and solvent composition.
Pigment wetting and dispersion.
Rheological structure at low shear.
Storage temperature and duration.

These variables should be evaluated together. A change in solvent blend or zinc source can alter storage behavior even when the organoclay dosage remains unchanged.

Anti-Settling and Redispersibility Are Different Properties
Anti-settling describes the formulation’s ability to limit particle movement and separation during storage.
Redispersibility describes how readily any settled material can be returned to a uniform suspension.
A useful evaluation must measure both.


The amount of sediment alone does not establish storage quality. Its consistency and the effort required to restore uniformity are equally important.

What Organoclay Contributes

Organoclay is an organically modified clay designed for compatibility with selected organic media. Suitable grades can develop a rheological network that supports pigments at rest and allows easier flow under shear.

Manufacturer literature describes organoclays for epoxy and zinc-primer applications that provide thixotropic behavior, suspension control and sag resistance. These benefits depend on selecting a compatible grade and incorporating it effectively.

Three aspects of rheology deserve separate attention:

Structure at rest.
Low-shear behavior helps determine whether zinc particles remain suspended during storage.
Flow under shear.
Mixing, pumping and spraying require the formulation to flow under the conditions imposed by the equipment.
Recovery after shear
.After application, structural recovery contributes to sag control. Its speed must also remain compatible with leveling.

A single viscosity reading cannot describe all three. Comparing formulations only by KU or one rotational-viscosity result can therefore overlook important differences.

Selecting a Grade for the Actual Resin–Solvent System
“Suitable for epoxy” is a starting point, rather than a complete selection criterion.
Epoxy primers can contain different resin types, solvent combinations and solids levels. These differences influence organoclay wetting, dispersion and rheological efficiency.

Suppliers should therefore receive information about the actual formulation, including:

Epoxy resin type and supplied solids content.
Solvent identities and approximate proportions.
Zinc content, particle size and morphology.
Existing wetting, dispersing and rheology additives.
Available manufacturing equipment.
Required storage and application performance.

Polarity is especially relevant. For example, Elementis identifies BENGEL 828 for medium- to high-polarity solvent systems, including epoxy coatings, and discusses its use in demanding zinc-rich primer formulations. This illustrates why grade selection should follow the formulation environment.

Dispersion and Activation Must Follow the Grade
Different organoclays have different incorporation requirements.

Some conventional grades require a polar activator and substantial shear to develop their intended performance. Other grades are designed for easier incorporation without a separate activator. These approaches should not be treated as interchangeable.

For example, the technical literature for CLAYTONE-MPZ specifies high shear with a polar activator, whereas BENGEL 828 is described as not requiring a separate polar activator.

Before increasing dosage, check:
Whether the powder is fully wetted and dispersed.
Whether the addition sequence follows the grade’s guidance.
Whether the equipment supplies sufficient shear.
Whether an activator is required and compatible.
Whether the final solvent and additive package changes the response.

Poor incorporation can make a suitable grade appear ineffective. Increasing the amount may then raise cost without correcting the underlying process problem.

Why More Organoclay Is Not Automatically Better

Increasing organoclay dosage is one possible response to settling, but it should be assessed alongside application performance.

As a formulation-development consideration, stronger structure may increase mixing resistance or impair spray behavior and leveling. The extent of these effects must be measured in the actual primer.

A practical approach is to compare several dosage levels within the selected supplier’s recommended range while holding other variables constant.

Choose the level that meets storage requirements while maintaining acceptable:
Remixing effort.
Spray atomization.
Sag resistance and leveling.
Film appearance.
Performance after hardener addition.

For two-component products, evaluate both the stored zinc-containing component and the mixed primer. Storage stability before mixing does not establish application behavior throughout the working period.

Preserve the Primer’s Protective Function
Rheology improvements must be considered alongside corrosion protection.

Research on zinc-rich primers emphasizes that zinc particles require electrical contact with the steel substrate to provide cathodic protection. Accordingly, changes in additives and pigment distribution should be validated in the cured coating rather than judged solely by liquid-paint stability.

A successful organoclay adjustment should therefore pass the formulation’s existing requirements for film formation, adhesion and corrosion performance.

Improved suspension is valuable, but it is only one part of a functioning protective coating.

Discuss the Failure Mode Before Choosing the Additive
The most useful supplier discussion starts with a clear description of the problem.

Does zinc settle rapidly? Does a hard bottom deposit form? Is the primer difficult to spray? Does rheology change after hardener addition? Does the problem appear only after warm storage?

Each observation points toward a different investigation.

For manufacturers evaluating organoclay, sharing the resin–solvent system, zinc characteristics, production method and storage observations provides a stronger basis for sample selection than requesting a general-purpose anti-settling powder.
The best-performing grade is the one that delivers reproducible suspension, practical remixing and acceptable application behavior in the actual epoxy zinc-rich primer.