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D2697-22 – Standard Test Method Technical Guide
🧪 Overview of the Archimedes Method
Standard Test Method D2697−22 provides a direct measurement of the volume percentage of nonvolatile matter (Volume NVV) in clear and pigmented coatings. This method is critical for determining the true volume solids of a coating, which directly impacts application spreading rate calculations and wet film thickness specifications. Unlike weight-based methods (such as D2369), this method measures the actual space occupied by the binder and pigments in the dry film.
The principle is based on the Archimedes buoyancy effect. A stainless steel disk is weighed in air and in a liquid of known density to determine its volume. After the disk is coated with the test material and dried, the disk and dried coating are weighed again in air and in the liquid. The volume of the dried coating is calculated by dividing the difference in buoyant forces (weight loss when submerged) by the density of the immersion liquid. An interlaboratory study established precision for several coating types, including a water-reducible exterior latex paint, a solvent-reducible primer surfacer, water-reducible primer surfacers and topcoats, and an acrylic dispersion lacquer topcoat. Radiation-curable materials are explicitly excluded from this test method (see Test Methods D5403).
⚙️ Procedure and Immersion Liquid Selection
The test procedure requires careful selection of the immersion liquid to ensure the dried coating film is not chemically attacked, dissolved, or leached. The standard specifically warns against using water for coatings that contain water-leachable ingredients or for low-gloss films that are poorly wetted by water. Similarly, organic solvents must not be used if they dissolve any component of the coating, such as monomeric plasticizers in lacquers.
The following table summarizes the recommended immersion liquids and their primary applications:
| 🟦 Immersion Liquid | ✅ Recommended Application | ⚠️ Critical Limitations |
|---|---|---|
| Distilled Water | Suitable for most paints and coatings | Not for films with water-sensitive leachable components or poorly wetted surfaces. |
| Low-Solvency Hydrocarbon Solvent (KB < 36) | Preferred for coatings poorly wet by water (e.g., mineral spirits, kerosine) | Must be avoided if the dried film contains solvent-soluble plasticizers or resins (e.g., lacquers). |
| Mercury (Special Modifications) | Coatings formulated above the Critical Pigment Volume Concentration (CPVC) | Requires specialized handling and modifications not specifically detailed in the standard. |
⚡ Important Note for Operators: A surfactant may be added to distilled water to improve the wetting of the film surface. However, the user must rigorously verify that the chosen immersion liquid does not swell, dissolve, or otherwise alter the properties of the dried coating film during the measurement period. The density of the immersion liquid must be determined accurately, per Test Method D1475.
📊 Key Measured Properties and Referenced Standards
The primary result from D2697 is the Volume Nonvolatile Matter (% NVV). This value represents the true volumetric solids content of the coating, which is an essential metric for formulating paints and predicting their performance.
The test method references several critical companion standards for supporting measurements:
| 📐 Referenced Standard | 🎯 Function in the Test Method |
|---|---|
| D1475 | Determines the density of the liquid coating and the immersion liquid. |
| D2369 | Establishes the volatile content, providing a complementary weight-based metric
📥 Standard Documents Download |