Gypsum board, also known as drywall or wallboard, is mandated by the building codes because it provides important passive fire resistance. This is why it is so important to replace drywall correctly. It is a primary means of protecting occupants from fire.
In the event of any water damage to drywall, precautions must be taken to prevent development and growth of mold. After flooding, exposure to raw sewage and other contaminants is another significant concern that must be abated. Only a knowledgeable building professional who can evaluate an impacted site in person can offer a set of specific remediation actions. The following document, housed on the Centers for Disease Control and Prevention (CDC) website, provides important information on cleaning up after flooding: Homeowner’s and Renter’s Guide to Mold Cleanup After Disasters.(PDF)
The Gypsum Association’s technical documents are not site-specific prescriptions, but rather guidance documents that outline best practices and provide consumers, building professionals, code officials, inspectors, and building product distributors with important information on repair and replacement methods, how to identify code-compliant gypsum panel products, and appropriate drywall handling and storage procedures. Gypsum Association recommendations related to water and flood damage and other pertinent considerations are contained in the following technical documents:
- GA-231-2019 Assessing Water Damage to Gypsum Board
- GA-235-2019 Gypsum Board Typical Mechanical and Physical Properties
- GA-238-2016 Guidelines for Prevention of Mold Growth on Gypsum Board
- GA-801-2017 Handling and Storage of Gypsum Panel Products
- GA-1000-2017 Identification of Gypsum Board
Q) How do I prevent mold growth on gypsum panels?
A) Gypsum board must be kept dry at all times to prevent the growth of mold. Review publication GA-238-2016 Guidelines for Prevention of Mold Growth on Gypsum Board. This quick reference publication addresses transportation, storage, handling, application, and maintenance guidelines.
Q) Is there a way I can tell if wallboard is “too wet” based on the reading from a moisture meter or something similar?
A) The answer is no. There is no industry standard that specifies an acceptable level of free moisture content in wallboard (bear in mind gypsum itself is 21% by weight chemically combined water). Further, moisture meters are very poor at indicating whether gypsum panels are too wet to use, not only because there is no established level of acceptable free moisture, but also because meters are designed to gauge relative moisture, e.g. to identify wetter and dryer boards.
Q) How do I know whether or not to replace gypsum board after it has been submerged in a flood?
A) You will want to reference GA-231-2019 Assessing Water Damage to Gypsum Board. Most notably, a gypsum panel that has been exposed to sewage or flood waters must be replaced. The levels of bacteria, such as E. coli, can be hundreds of times above safe levels in flood water. Also, hydrocarbons from underground gas storage tanks and fuel leaks from submerged vehicles can be present. Often, the board will need to be removed anyway to assess the underlying substructure.
Q) Is there a way to ensure that the gypsum board selected for my home restoration is code compliant?
A) Reference GA-1000-2017 Identification of Gypsum Board. This two-page publication will help you identify the criteria that are enforced in the United States and Canada for the sale and installation of gypsum board. Ensuring you are using gypsum board that meets the ASTM C1396 Standard Specification for Gypsum Board standard will help avoid code violations. Gypsum board manufactured by Gypsum Association member companies conforms to all requirements of ASTM C1396. Never use drywall that is not labeled appropriately. Building codes throughout the United States require each individual sheet of gypsum board have the following information legibly printed on the back surface of each board, parallel to the bound edge of the board:
- The name of the manufacturing company or a unique alpha code identifying the name of the manufacturing company. The decision to print the name of the company or to create and use a unique code is at the discretion of the company.
- A code identifying the manufacturing facility and, where applicable in a multi‐line facility, the production line.
- A code identifying the date and time of manufacture.
- The country of manufacture as designated by the three letter code in ISO 3166‐1. The code for the United States is USA. The code for Canada is CAN.
Q) What is the proper way to store gypsum board on a project site to prevent moisture damage?
A) Pages 8 and 9 of GA-801-2017 Handling and Storage of Gypsum Panel Products describes guidelines for stocking gypsum panel products on job sites. These two pages note that gypsum panel products shall be delivered just prior to installation time. This practice helps minimize damage to the material and reduces the risk of mold growth in surrounding areas of elevated moisture. GA-801 also notes panels must be kept in an enclosed covered, dry area, such as a garage, to minimize exposure to rain, etc.