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Moisture Resistant Drywall

Water and drywall don't mix. The high humidity and exposure to water in bathrooms, laundry rooms and kitchens is a breeding ground for mold and mildew. Sugars and starches used to bind gypsum in traditional wallboard also provide a food source for mold, mildew and insects.

The three most commonly used products in rooms with higher humidity are green board, backerboard and cement board. Green board has higher moisture resistance that normal drywall due to a petroleum-based treated paper cover over the gypsum. However, green board is not a waterproof product and it shouldn't be used in areas that will experience direct contact with water.

Three different levels of moisture need to be considered when choosing the type of gypsum board.

  • Direct water contact like showers and shower
  • Intermittent water contact like tub surrounds and kitchen backsplashes
  • Areas that are subjected to high humidity like laundry rooms and adjoining areas outside of showers or bathtubs.

Green board or moisture/mold resistant gypsum boards are good for areas with higher humidity but not for intermittent or direct water contact. A tile backerboard should be used in areas of intermittent water and if the surface is to be tiled or painted. For areas that will receive direct water exposure and be tiled, cement board is required. IRC R702.3.8 and R702.4.2

Questions for Rick:

  • Is blue board to be used in any areas with high humidity or water?
  • Greenboard – high humidity
  • Has IRC removed this as code for baths?
  • Is industry using this anymore?
  • Tile backerboard for intermittent water and for tile or painted finish?

Cement Board direct water and tile? Is this used anywhere else? Is there any other finish other than tile? How is the transition between cement and other wallboard accomplished Does Definitive have a brand they use exclusively unless specs request differently? Any special techniques used for areas susceptible to mold/moisture?