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D4897 – Standard Test Method Technical Guide
📐 Scope and Product Classification
ASTM D4897/D4897M − 16 (Reapproved 2023) covers an asphalt-impregnated and coated glass-fiber base sheet designed specifically for venting applications in roofing systems. This base sheet is intended for use as the first ply of a roofing membrane and is classified exclusively as Type II—Heavy-duty. The fundamental design provides for the lateral release of pressure in roofing systems due to the coarse mineral granules on the bottom side, which create an open, porous channel in the horizontal plane beneath the membrane. The base sheets shall be permitted to be with or without perforations or embossings.
⚠️ Strict Unit Compliance Required: The values stated in either SI units or inch-pound units are to be regarded separately. Each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with this specification.
⚙️ Materials and Manufacture
The reinforcement consists of a thin, porous mat of uniformly distributed glass fibers, bonded with a water-resistant resinous binder. The mat may also include reinforcing strands or glass yarns. During the process of manufacture, the glass mat is impregnated and coated on both sides with a hot asphaltic coating, with or without a mineral stabilizer. The bottom side is surfaced with coarse mineral granules embedded in an asphaltic coating, while the top side is surfaced with fine mineral surfacing. Per the standard, the product is permitted to be embossed or unembossed on the bottom side and may contain holes designated for attachment with mopping asphalt.
📊 Physical Requirements and Performance Validation
The material at the point of manufacture must conform to specific physical requirements, dimensions, and masses. The finished product must withstand field handling without damage. It shall not crack nor be so sticky as to cause tearing or other damage upon being unrolled at temperatures between 10 °C and 60 °C [50 °F and 140 °F]. Pliability is strictly evaluated at 25 °C ± 1 °C [77 °F ± 2 °F], where at least eight out of ten test strips must not crack when tested in accordance with the procedures outlined in the standard.
| 🟦 Parameter | 📐 Specification / Value | 🎯 Performance Criterion |
|---|---|---|
| Product Type | Type II | Heavy-duty venting base sheet |
| Mat Reinforcement | Uniform glass fibers, water-resistant resinous binder | Coated on both sides with hot asphaltic coating |
| Bottom Surfacing | Coarse mineral granules | Lateral release of pressure / venting channel |
| Top Surfacing | Fine mineral surfacing | Protection of the asphaltic coating |
| Unrolling Conditions | 10 °C to 60 °C [50 °F to 140 °F] | No cracking, stickiness, or tearing |
| Pliability Test | 25 °C ± 1 °C [77 °F ± 2 °F] | At least 8 out of 10 strips no crack |
💡 Design Options and Terminology: The product is permitted to be embossed or unembossed on the bottom side and may contain perforations or holes for mopping asphalt. For complete definitions of terms used in this specification, refer to Terminology D1079.