Cement Board

• Cement board is a type of panel product, like the more widely used gypsum board. It is constructed from Portland cement, so it is both sturdier and heavier than gypsum board. The cement core is reinforced by an outer casing of fiberglass mesh. It comes in standard sizes of panels that are 5 feet long, 1/2 inch thick and either 32 or 36 inches long. The standard sizes are designed to make it easy to install in tub and shower enclosures.
  
  

Water Issues

• Cement board is usually used in areas that are at high risk for moisture or water exposure, such as bathrooms or kitchen counters. Water cannot easily penetrate its cement core, and the board as a whole does not deteriorate when it is exposed to water. However, water damage can occur when water manages to soak through the cement board and reaches the framing boards that make up the walls. The cement board isn’t damaged, but portions of your home’s structure behind it are.
  
  

Prevention

• To protect the studs and other framing structures behind cement board, use a water barrier. Before installing cement board, install 4-mil plastic or 15-pound building paper. They are waterproof, and if there is a flood in your bathroom, any water that gets through the cement board will be stopped by them. After installing the water barrier, install the cement board as you normally would.
  
  

Considerations

• When installing cement board, you can reduce the risk of water damage to studs and other supports by following the manufacturer’s recommendations. Use cement board screws, which are also water resistant, and use cement board joint tape and mortar. If you substitute standard drywall tape and joint compound, they may let water get through the cement board.