Resources & Guides / Building Codes & Standards / ASTM & UL Standards / ASTM C630
ASTM C630 (Withdrawn)
Water-Resistant Gypsum Backing Board - REPLACED BY ASTM C1396
⚠️ This Standard Has Been Withdrawn
ASTM C630 has been withdrawn and is now obsolete. Use ASTM C1396, Water-Resistant Gypsum Board as the modern equivalent.
Historical Overview
ASTM C630 was the historical standard for what is commonly known as "green board" - water-resistant gypsum board designed primarily as a substrate for ceramic or plastic tile in moisture-prone areas like bathrooms and kitchens. Its requirements have been incorporated into the comprehensive gypsum board standard ASTM C1396/C1396M under the section for "Water-Resistant Gypsum Board."
Critical Distinction: Water-Resistant vs. Waterproof
"Water-resistant" does not mean "waterproof." Water-resistant gypsum board resists degradation from intermittent moisture exposure and high humidity, such as in bathrooms with showers. It is NOT designed for direct and continuous water exposure. In tub or shower enclosures, water will eventually penetrate tile and grout, reaching the substrate.
If that substrate is water-resistant gypsum board, it will eventually soften, degrade, and support mold growth, leading to system failure. Building codes mandate true waterproof backer board (like cement board per ASTM C1325) or liquid-applied waterproofing membranes in wet areas.
Modern Replacement
Correct Specification: ASTM C1396, Water-Resistant Gypsum Board
- Suitable for walls outside shower/tub areas
- Appropriate for high-humidity environments
- NOT suitable for direct water exposure
- Must differentiate between "damp" and "wet" areas in specifications