What Is Greenboard Water Resistant Drywall?

Greenboard Drywall (with Regular Drywall Too)

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Drywall is a low-cost, easily obtainable gypsum-and-paper material that helps you quickly add wall covering to framed walls. Drywall is invaluable when putting up walls in just about any area of the home—kitchen, dining room, bedroom, general areas, and garages. But one place where drywall falters is in areas that experience a great deal of moisture: namely, shower and bathtub stalls.

What Is Greenboard Drywall?

Greenboard drywall is a type of drywall that is better suited for humid locations.

Greenboard Basics

  • Greenboard is a largely outdated term for water-resistant drywall
  • Should be used in high-humidity areas but not in areas that experience a great amount of water, such as shower stalls
  • Use cement backer board for shower stalls instead of greenboard

Greenboard Drywall Definition

Greenboard is a term that's occasionally used for a type of drywall that is used for walls in damp but not wet zones in a building. Originally, greenboard was used as a direct backer board for ceramic tile in highly wet areas such as showers or bathtubs but this usage began to be phased out in the 1990s. Cement backer board such as Durock is best used for tile in highly wet applications such as shower stalls, with greenboard and other water-resistant drywall panels kept only to high-humidity areas.

Greenboard's paper facing alone does not inhibit mold growth. The facing must be treated with mold-resisting agents. Greenboard is still manufactured and sold, but it is slowly being supplanted by paperless drywall that resists moisture and can be used in either dry or moist conditions.

Greenboard vs. Conventional Drywall

Greenboard's inner core of gypsum is the same as regular drywall. Also, just like normal drywall, greenboard is attached directly to the studs.

Two things about the outer covering of greenboard differentiate it from conventional drywall:

  • Greenboard's outer paper covering resists water but is not considered to be waterproof. Some greenboard is impregnated with compounds that deter the growth of mold.
  • Greenboard's paper cover is a sea-foam green on one side. The color imparts no special water-resisting properties, but it does serve two purposes. For one, it identifies this as moisture-friendly drywall. For another, it helps the installer better see where to apply the drywall compound.

Even without mold-resisting additives, the gypsum core of greenboard, like conventional drywall, does not support the growth of mold as it is not an organic product.

Fun Fact

Just like regular drywall, you can cut greenboard to size by gently running a sharp utility knife against a straightedge on the paper side. Once it's scored, you can snap off the section from the original sheet. 

Greenboard and Water Resistant Drywall Dimensions

Greenboard drywall comes in 1/2-inch and 5/8-inch thicknesses and conventional 4-foot by 8-foot sizes.

Even though greenboard drywall is the same thickness (5/8-inch) as Type X, it should not be confused with the Type X fire-resistant product. Type X should be used in areas such as kitchens where a fire might be expected. Type X drywall is required by building code for garages.

Greenboard and Water Resistant Drywall Brands

The type of drywall pejoratively called greenboard is found under various brand names such as GP's ToughRock Mold-Guard Drywall Panel and American Gypsum's Aquabloc. Greenboard costs slightly more than conventional drywall.

Is Greenboard Allowed for Wet Applications?

Technically, greenboard and other water-resistant drywall panels can be used in highly wet places. According to ASTM C 1396, Section 7, water-resistant drywall can be used in wet locations such as behind tile in bathtub or shower stalls. While greenboard drywall's paper covering is water-resistant, it is not waterproof. According to ASTM C473, after two hours of water immersion, the average water absorption for panels should not be more than 5-percent by weight.

Caution should be taken when using greenboard and other water-resistant drywall panels for ceiling applications. Ceiling panels can sag when subjected to high humidity conditions or to textures and finishing materials that contain moisture.

Water-Resistant Drywall vs. Cement Board

Cement-based backer boards Durock, Wonderboard, and Hardibacker are all mineral-based or cementitious materials. Cement board is perfect for tile-covered wet applications like showers and tub surrounds. Wet or dry, such backer board provides a stable base for tiling.

The organic element to drywall's paper is the chief reason why drywall may experience mold and mildew. Another advantage of the cement board is that it can be used as a base for tile flooring; drywall of any type can never be used for flooring applications.

One reason why builders may use greenboard for highly wet areas, though, is because it is faster and easier to install and less expensive on a square-foot basis.

It is best to use greenboard or other water-resistant drywall in the large areas of bathrooms, kitchens, and other areas where the drywall may be subjected to lightly damp conditions, humidity, and the occasional minor splashes of water. Using greenboard drywall in a highly wet location is possible but cementitious materials are a better product for that location. At the least, severe mold growth will occur with drywall. Sag and outright failure may occur when the drywall has been subjected to an abundance of water.

Also consider a drywall product that has a fiberglass coating instead of paper. It is rated higher than "greenboard" in moisture and mold resistance.

Greenboard and Water Resistant Drywall Uses and Locations

Greenboard: Not Acceptable

  • Shower stalls
  • Tiled bathtub enclosures
  • Water-prone basement walls
  • Saunas
  • Steam rooms

Greenboard: Acceptable

  • Bathtub enclosure, pre-fabricated
  • Basement areas other than bathing facilities
  • Kitchen, near sink
  • All other dry or damp areas
Article Sources
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  1. ASTM C1396 / C1396M - 17. ASTM International - Standards Worldwide