Green board is being installed behind an existing bathtub.
Gypsum board, drywall, Sheetrock, what ever name you want to call it, wall board used to be just one thing. Wall board now comes in many different types with differing amounts of insulation, sound transmission and moisture resistance ratings. Knowing the difference between blue board and green board can determine whether the building inspector approves the newly installed bathroom; or requires it to be torn out and redone.
Wall board
Wall board was designed as a replacement for plaster and lath walls. Prior to World War II, interior walls were made of wood strips, called lathes, nailed horizontally across the studs. The Lathes were then coated with two or more layers of plaster. Because the plaster had to be applied smoothly and evenly to every wall in a room only a highly-skilled worker could apply plaster. Additionally, a lot of drying time was needed between coats. Because of the labor costs and the time involved, plaster and lath walls are very expensive.
Wall board is made of gypsum, a mineral, sandwiched between two layers of paper. A 4-foot by 8-foot sheet of wall board can be installed in a few minutes by an unskilled laborer. Joints and fasteners in wall board must be concealed using wall repair compound, often called mud, and paper tape. This finishing work can be done by a home owner or a professional.
Green Board
Green board is a type of wall board treated to resist moisture. Wall board is faced with paper. When exposed to moisture, the paper passes the moisture to the gypsum, which swells and falls apart. Green board does not allow the moisture to attack the gypsum. It is called green board, because the facing paper is colored green for easy identification on the job site.
Green board is not waterproof and should not be installed where it will be constantly exposed to water.
Blue Board
Blue Board is another specialized variety of wall board. It is designed to receive a thin coat of plaster over the entire surface, instead of just over the joints. The paper facing, colored blue, is designed to absorb the moisture from the plaster and create a strong bond between the plaster and the gypsum.
Because the entire face of the blue board wall must be coated with plaster, instead of only covering the joints; installation costs for blue board walls are much higher than standard wall board.
The Right Material for the Job
Green board is water resistant, while blue board is designed to absorb water. In addition to blue and green board, there are varieties of gypsum wall board designed to be fireproof, soundproof and waterproof. Based on your local building code different types of wall board will be mandatory, optional or prohibited for any particular project.
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