What Is It?
Greenboard is a type of drywall that is used for in lightly damp areas. Experts and industry professionals debate this point, but consensus is that greenboard should not used in highly wet applications such as shower stalls.
Greenboard alone does not inhibit mold growth. It must be treated with mold-resisting agents.
Greenboard vs. Regular Drywall
Greenboard's inner core of gypsum is the same as regular drywall.
Also, just like normal drywall, it is attached directly to the studs.
Two things about the outer covering are different:
- Better Water Resistance: Its paper covering resists water (but is not water-proof). Some greenboard is impregnated with compounds that deter the growth of mold.
- Color: This paper cover is a sea-foam green on one side. The color imparts no special water-resisting properties, but it does serve two purposes: it identifies this as water resistant drywall; it helps the installer better see where he/she is applying 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.
Sizing and Brands
Greenboard drywall comes in 1/2" and 5/8" thicknesses and conventional 4' by 8' sizes.
Terms "greenboard" and "green board" are not official and are infrequently seen in company literature or at retailers.
Instead, look for drywall advertised as being "mold resistant" or "water resistant."
Carried under such brand names as GP's ToughRock Mold-Guard Drywall Panel and American Gypsum's Aquabloc, greenboard runs about $1 more per 4' x 8' panel than conventional drywall.
Greenboard: Allowed For Wet Applications or Not?
According to ASTM C 1396, Section 7, water resistant drywall can be used in wet locations such as shower stalls.
While greenboard drywall's paper covering is water-resistant, it is not waterproof. According to ASTM C473, after 2 hours of water immersion, the average water absorption for panels should not be more than 5% by weight.
Check to see if your local code allows for this.
For Homeowners, The Question Is Different
But the question boils down to one thing:
If it is possible to install cement board in the few, small spaces that are considered "highly wet," why not do this?
This may be a more critical question for contractors who are trying to pare down the cost of materials. But for DIY homeowners, the extra cost of cement board is insignificant when compared to the high costs
Mortar and cement-based backerboards Durock, Wonderboard, and Hardibacker are all cementitious, "like" materials. Cement board is perfect for tile-covered wet applications like showers and tub surrounds. Wet or dry, backerboard provides a stable base for tiling.
Instead, use greenboard 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 wet location is a recipe for disaster.
At the least, severe mold growth will occur, if not outright failure of the product.
Not Fire Resistant
Even though greenboard drywall is the same thickness (5/8"), it should not be confused with the fire-resistant product named Type X. Type X should be used in areas such as kitchens where fire might be expected.
Recommended Uses and Locations
|Location||Use Green Board?|
|Shower Stall Walls||No|
|Bathtub Enclosure (Tiled)||No|
|Bathtub Enclosure (Pre-Fab)||Yes|
|Water-Prone Basement Walls||No|
|Basement Areas Besides Bathing Facilities||Yes|
|Saunas, Steam Rooms||No|
|Kitchen, Near Sink||Yes|