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D1668 – Standard Test Method Technical Guide
📐 Scope and Classification of Fabric Treatments
This specification covers finished woven-glass fabrics coated with either asphalt, coal-tar pitch, or an organic resin compatible with roofing, waterproofing, or other usages. The standard designates D1668/D1668M and classifies fabrics into three distinct types based on the treatment applied.
| 🟦 Type | 🎯 Treatment | 📌 Usage Recommendation |
|---|---|---|
| I | Asphalt Treated | Suitable for use with all asphalts and asphalt-based compounds. |
| II | Coal-Tar Pitch Treated | Suitable for use with all coal-tar pitches and coal-tar pitch-based compounds. |
| III | Organic Resin Treated | Compatible with the plying liquid materials specified. The organic resin must not be water soluble. |
⚠️ Application Specifics: Per Note 1 of the standard, the purchaser may specify the use of Type I or Type II fabrics for roofing systems using bitumens other than their primary treatment base, ensuring cross-compatibility where agreed upon.
⚙️ Materials, Manufacture, and Dimensional Standards
The untreated greige scrim (open basket weave) or leno (locked weave) fabrics must conform to the requirements of Table 1 within the standard. During manufacturing, the glass fibers must be thoroughly and uniformly coated without injuring the weave. Glass fabric is typically woven in specific nominal widths.
| 📏 Width (SI) | 📐 Width (Inch-Pound) | ⚡ Manufacturing Detail |
|---|---|---|
| 0.91 m | 36 in. | Standard single width. |
| 1.83 m | 72 in. | Includes extra warp threads for slitting into 0.91 m widths. |
| 2.74 m | 108 in. | Includes extra warp threads for slitting into 0.91 m widths. |
Wider rolls feature a “dupe” selvedge with a brush edge created by the cut fill threads, allowing for efficient slitting into incremental widths while maintaining fabric integrity.
💡 Unit Systems Compliance: The values stated in either SI units or inch-pound units are to be regarded separately as standard. Combining values from the two systems may result in nonconformance with the standard, as specified in Section 1.2.
📊 Key Physical Properties and Test Methods
Compliance with D1668 requires rigorous testing to ensure the fabric meets specified physical properties. Testing is performed according to several critical ASTM standards.
- 🔍 D146/D146M — Standard test methods for sampling and testing bitumen-saturated felts and woven fabrics for roofing and waterproofing.
- 📏 D3775 — Standard test method for end (warp) and pick (filling) count of woven fabrics.
- 📐 D3776/D3776M — Standard test methods for mass per unit area (weight) of fabric.
- ⚡ D579/D579M — Specification governing the greige woven glass fabric prior to treatment.
Definitions for terms used in this specification can be found in Terminology D123 and D1079.
❓ Frequently Asked Questions
🔍 What are the primary classifications of glass fabric under ASTM D1668?
Fabric treatments are classified into Type I (Asphalt Treated), Type II (Coal-Tar Pitch Treated), and Type III (Organic Resin Treated). The required organic resin for Type III must be agreed upon by the purchaser and supplier and must not be water soluble.
💡 What is the significance of the “dupe” selvedge in wider glass fabrics?
Fabric woven in 1.83 m (72 in.) and 2.74 m (108 in.) widths includes extra warp threads with slitting spaces. This allows the manufacturer to split the wide roll into standard 0.91 m (36 in.) increments. The resulting cut edge is a “brush” edge made from cut fill threads rather than a smooth wrapped selvedge.
⚡ Can Type I or Type II fabrics be used with non-standard bitumens?
Yes, as indicated in Note 1. Although Type I is asphalt-treated and Type II is coal-tar treated, the purchaser may specify either type for systems using other bitumens if the system is compatible.
📌 What test methods are critical for verifying conformance to D1668?
Key test methods include D146/D146M for overall sampling and testing, D3775 for thread count, D3776/D3776M for weight/area, and conformance to D579/D579M for the raw greige fabric.