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D4446 – Standard Test Method Technical Guide
ASTM D4446/D4446M-13 is a standardized test method for evaluating the anti-swelling effectiveness of water-repellent formulations on wood and measuring the differential swelling of untreated wood in liquid water environments. It serves as a qualitative screening test for dimensional stability.
📐 Specimen Geometry and Dimensions
Test specimens are elongated slats prepared from straight-grained, flat-sawn, clear, kiln-dried Ponderosa pine sapwood or other suitable species. The standard dimensions are 6 mm (1/4 in.) in the longitudinal direction and 38 mm (1 1/2 in.) in width, with lengths corresponding to 5 in. or 10 in. wafer sizes for the swellometer apparatus.
| 🟦 Property | 📏 Value |
|---|---|
| Wood species | Ponderosa pine sapwood |
| Longitudinal dimension | 6 mm (1/4 in.) |
| Width | 38 mm (1 1/2 in.) |
| Length options | 5 in. or 10 in. |
⚙️ Test Procedure and Conditions
Wood slats are immersed in the water-repellent formulation, conditioned with appropriate weighing, and then subjected to immersion in distilled water for a prescribed period. Untreated slats omit the water-repellent immersion for comparison. Swelling is measured using a dial gage calibrated in increments of 0.025 mm (0.001 in.). All conditioning and testing must be conducted in a controlled environment at 23 ± 2°C (73.5 ± 3.5°F) and 50 ± 5% relative humidity.
⚠️ Critical: The conditioning room must maintain constant temperature and humidity throughout the test to ensure uniform moisture content in all specimens.
| 🟦 Parameter | 📏 Requirement |
|---|---|
| Temperature | 23 ± 2°C (73.5 ± 3.5°F) |
| Relative humidity | 50 ± 5% |
| Balance sensitivity | At least 0.01 g |
| Dial gage increment | 0.025 mm (0.001 in.) |
📊 Key Measured Properties
The primary metric is anti-swelling efficiency (ASE), with a pass requirement of 60% as per Section 2.2. The method also quantifies differential swelling of untreated wood species after water immersion. This qualitative screening test provides a reproducible basis for comparing water-repellent formulations and wood species.
💡 Technical Note: Water-repellent formulations should be mixed until uniform and applied by brush, roller, dip, or spray to exterior wood surfaces for accurate evaluation.
❓ Frequently Asked Questions
🔍 What is the pass requirement for anti-swelling efficiency?
A water repellent efficiency of at least 60% is required to pass the test.
💡 What wood species is recommended for testing?
Ponderosa pine sapwood is the standard species, but others can be specified.
⚡ How is swelling measured?
Swelling is measured with a dial gage having increments of 0.025 mm (0.001 in.).
📌 What are the conditioning requirements?
Specimens are conditioned at 23 ± 2°C (73.5 ± 3.5°F) and 50 ± 5% relative humidity.