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D5007-99 – Standard Test Method Technical Guide
🎯 Scope and Key Terminology
ASTM D5007-99 (2024), officially titled Standard Test Method for Wet-to-Dry Hiding Change, establishes a visual procedure for evaluating the alteration in hiding power of an architectural coating as it transitions from a wet to a dry film. The test is specifically designed for white and light-tinted coatings (per Section 1.2). Values are stated in SI units and are regarded as standard.
The method relies on assessing the difference between the hiding index of the wet film (hSW) and the dry film (hSD) using a visual comparator set to a standard contrast endpoint.
| 🟦 Term | 📐 Symbol | 🎯 Definition per Standard |
|---|---|---|
| Hiding Index | hS | The Spreading Index at a standard film opacity at a contrast ratio of 0.98 (98%). |
| Hiding Index (Wet) | hSW | The hiding index measured immediately after application using the logicator. |
| Hiding Index (Dry) | hSD | The hiding index measured after the film has dried under standard conditions. |
| Logicator | — | A multi-notch applicator with clearances corresponding to wet film thicknesses and spreading rates in equal percentage steps. |
💡 Method Core: The “just-short-of-complete-hiding” standard used here is a 0.98 (98%) contrast ratio. This aligns with the endpoint defined in the photometric Test Method D2805 but is evaluated visually. The same physical comparator must be used for evaluating both the wet and dry film readings.
⚙️ Apparatus and Test Procedure
The primary apparatus includes a standard black and white hiding power chart and the specialized “Logicator” applicator, which applies several stripes of the test paint in a single drawdown. Each stripe represents a different, precisely calibrated spreading rate. All conditioning and testing must be performed in an environment conforming to ASTM D3924.
Summary of the Standard Procedure:
- Prepare a drawdown of the test paint on the hiding power chart using the logigator.
- Immediately evaluate the wet film by comparing each stripe to the 0.98 contrast ratio standard. Determine which stripe most closely matches and record its hiding index as hSW.
- Allow the film to dry completely under standard conditions.
- Repeat the visual evaluation on the dry film, determining and recording the hiding index as hSD.
📊 Evaluation of Wet-to-Dry Change
The Wet-to-Dry Hiding Change is expressed as the difference between the wet and dry hiding indices. If the index decreases upon drying (hSD is less than hSW), the paint formulation suffers from a loss of opacity known as “dry hide loss.”
| 📏 Observation | ⚡ Contrast Ratio Target | 🟦 Hiding Index |
|---|---|---|
| Standard Endpoint (Just short of hiding) | 0.98 (98%) | Standard comparator |
| Wet film matching the standard | 0.98 | hSW |
| Dry film matching the standard | 0.98 | hSD |
| Final calculated change | — | ΔhS = hSW – hSD |
⚠️ Low Hiding Paints: For paints with unusually low hiding power, the standard 0.98 contrast ratio may lie outside the range of the applied stripes. In such cases, Section 3.1.1.1 specifies that the visual standard should be one of the stripes from the test drawdown itself.
❓ Frequently Asked Questions
🔍 What exactly is a “Logicator” applicator?
It is a multi-notch applicator defined in Section 3.1.3. Its clearances correspond to wet film thicknesses and spreading rates in equal percentage steps. The scale on the logicator provides values directly related to the logarithms of these spreading rates.
💡 Why is a 0.98 (98%) contrast ratio used as the standard endpoint?
This value is universally accepted as the visually defined endpoint of “just-short-of-perfect-hiding.” It correlates to a visual color difference of approximately 0.75 CIELAB units, aligning this visual method directly with the standard photometric hiding power method in ASTM D2805.
⚡ What does it mean if the hiding index decreases during drying (hSD < hSW)?
This indicates that the paint film loses hiding power as it dries, a phenomenon often referred to as “dry hide loss.” This typically results from pigment crowding or orientation changes during solvent or water evaporation, meaning the dry film requires a higher spreading rate to achieve the same opacity.
📌 Why is this test method not recommended for colors other than white and tints?
Section 1.2 of the scope explicitly limits the method. The visual estimation of a contrast ratio near 98% is exceedingly subjective and difficult to perform accurately when evaluating deep or saturated chromatic colors, making the standard comparator unreliable.