Greenboard and blue board are both types of drywall but they are very different in terms of functionality. Many people haven’t heard of either, but it’s very worthwhile knowing about them both. They can prove useful in your home construction work and can be used alongside regular drywall.
In many ways, blue board is just like drywall but it is of a much higher quality. It’s available in the same sizes and can be treated in much the same way when it comes to cutting and fastening into studs. At its core, it’s exactly the same but treated with gypsum. The main difference is in the blue covering, which is where blue board gets its name. It not only looks different, but it actually is a different composition. It’s specially treated so that plaster that’s formulated for it adheres better.
Blue board doesn’t requite several coats of joint compound in order to be smooth. Instead, it only needs plaster and tape on the seams followed by a thin coat of the plaster no more than 1/8 of an inch thick. Blue board is also much better than regular drywall at eliminating issues like dents and paint problems. The blue coating and the way it holds also helps to make the joints far less visible. Once coated, the blue board can be painted just like any other drywall.
It should be noted that blue board can cost 20 percent more than regular drywall and it takes skill and practice in order to use the special plaster properly (the plaster is also more costly than regular joint compound). Although blue board can save time, the savings will be negated if you don’t know how to work with the materials properly.
Greenboard is a type of drywall rather than a brand name, as several different manufacturers make it. It costs more than regular drywall and its thickness means it needs to be used next to the thickest form of regular drywall. Also, since it's more expensive than regular drywall, it should only be used where appropriate to cut down on extra costs.
Greenboard is also very much like traditional drywall. The two differences are the thickness (it's a little thicker than drywall) and the green covering which is resistant to water. This makes greenboard ideal for situations where there will be high humidity or water being splashed. It’s good for bathrooms, kitchens, and all kind of damp applications. Greenboard will do very well in a basement, for example, which can easily become damp. It will prevent moisture from entering the drywall and can cut down on the possibility of mold and mildew in the basement.
However, it has to be emphasized that it’s only good for damp applications and not wet applications. You shouldn’t use greenboard for shower walls even with tile on top. If the green covering becomes soaked, water will seep through into the gypsum and it will disintegrate. There are ways that it can be used, but it is better not to take the risk if you can't be completely confident with the results.
There is a type of drywall (called Type X) that is fire-resistant, but greenboard is not fire resistant and neither is blue board.