What You Should Know about Water-Resistant, Greenboard Drywall
Whether you’re building a new bathroom in your home, or you’re remodeling a section of your house that’s exposed to humidity, it’s important to know about greenboard and where it’s appropriate to use it. It’s a product that’s good in several sections of the home, and something that you’ll want to use instead of standard gypsum board also known as drywall.
What is Greenboard?
Greenboard is a water-resistant gypsum board or drywall panel that came out in the 1960’s. The product is essentially a more durable gypsum board. It has the same gypsum core that you’ll find on standard drywall all over homes, but it comes with a thicker coating of paper that’s protected by wax for water resistance. The exterior paper has a green tint to it helping to separate it from standard gypsum board, and leading to the product being known by most people as “greenboard”
While standard drywall comes in ¼” and ½” thicknesses, greenboard is sold in ½” and 5/8″ thicknesses. That’s something that you have to keep in mind if you’re replacing ¼” drywall in your home with greenboard. It’s thicker because of the added wax that’s infused into the material, and also because it has to be. Studies show that greenboard is actually weaker than standard drywall when it gets wet and the added thickness helps compensate for this. When installed properly the slightly weaker material isn’t a problem at all and offers superior moisture resistance.
It Isn’t Water Proof
Greenboard drywall isn’t designed to line the inside of showers or for use in environments exposed to outdoor weather. It’s the type of stuff that you want to use down in your basement or another part of your home that’s exposed to more humidity and moisture in the air. Greenboard drywall isn’t water-proof, it simply resists moisture better than the standard gypsum board that’s on most walls in homes around the United States.
It Isn’t Fire Resistant
There is a fire-resistant drywall product known as Type X that’s sold in 5/8″ sheets for use around fireplaces and other high-risk locations in the home. This is completely different than greenboard even though they are both available in the same size. It’s important to realize that greenboard drywall isn’t any more fire resistant than standard drywall is. If you’re looking for a fire-resistant product you’ll have to rely on something like Type X or another solution like Cement Board instead.
Properly Installing Greenboard
When installing greenboard on the walls of your home you can install it just like you would standard drywall. Cut the pieces to size using a sharp utility knife and a metal straightedge. Simply secure the straightedge in place and score through the outer paper coating using a fresh blade. Once the paper is scored you can snap the board off changing its overall size to what you need.
Installing it on Walls
When put on the walls of your home you can install water resistant drywall just like standard drywall. Drive drywall screws into the board and the studs behind it. Take care to only go just below the surface of the drywall and try to avoid going through the paper coating entirely. The gypsum core doesn’t hold fasteners as well and isn’t as strong to rely on during an installation. If you have to go with multiple rows of greenboard on a wall stagger the material to keep seams from lining up. While it will be more difficult to cover up your seams when it comes time to tape and mud them, staggered joints are stronger and more reliable.
Putting it on Ceilings
Special care must be taken when putting greenboard drywall on ceilings. It’s heavier and a bit weaker than standard drywall which can lead to sagging issues. To compensate for these problems it’s important to fasten the drywall every 12 inches instead of 16 inches. To do this you’ll want to strap your ceiling first. To do this purchase 1″x3″ lumber and fasten it perpendicular to the joists in your ceiling. This is a good practice to use when securing drywall on a ceiling in general because it makes installations simpler and more secure.
With the strapping in place you can install the greenboard with drywall screws used liberally. Drive the screws to just past the surface but avoid going through the paper entirely. This makes covering the screws easy but preserves the strength of the installation.
Why it isn’t Recommended for Bathroom Ceilings
Many local building inspectors will tell you to avoid putting water resistant drywall on your bathroom ceiling, and that’s actually for your own protection, even though using it that way may not be a problem. Greenboard weakens more than standard drywall does when it gets completely saturated. Since bathroom ceilings tend to collect a great deal of moisture this is a common weak point for the material. When you consider that a ceiling installation provides the greatest chance for failure of this product it’s easy to see why many inspectors would suggest a different material. When installed on a ceiling without enough fasteners greenboard is known to fail. In order for it to function properly it has to be installed with fasteners no more than 12″ apart, that’s something that most ceiling joists won’t accommodate without some modification. If you do want greenboard on your ceiling you can accomplish the installation safely by adding on some blocking to allow you to nail or screw the material every foot, but it’s generally easier to just go with a different material like standard drywall with a paint finish.
Finishing the Drywall
Once you have it all locked in place it is time to finish your greenboard installation. To do this you have to mud and tape it completely and put on a layer of protective paint. Coat every seam and all your screw holes with joint compound (also called mud) using a putty knife. Now use the putty knife to press drywall tape into each of the seams in between your panels and go back over them with another layer of the compound to cover them and really stick things in place. Allow this coating to dry and apply one to two more subsequent coatings evening the coatings out so it all blends well. With the compound covering the walls and ceiling you can begin painting. Before you start sand down any rough spots that you see, though there shouldn’t be many, and wipe away the dust with a damp cloth. Now prime and paint the walls using a durable paint designed for bathrooms and other damp environments. This completes your installation.
Greenboard Versus Cement Board
While greenboard and cement board are often compared to one another they are very different products with different purposes. Cement board is a better solution for use around showers or other locations that are going to get very wet, but it needs a moisture barrier behind it which takes more time to install and is more expensive than greenboard.
Greenboard is the faster and more affordable solution for sections of your home that are going to get damp but not really saturated. Greenboard doesn’t need the moisture barrier behind it that cement board does, but it can’t be relied upon to hold up to shower conditions either.
Greenboard isn’t good for every application, but when you know how to use it properly it can be a useful tool to keep your home functioning properly. Add it in the damp areas of your home to help prevent mold and mildew and you’ll have fewer problems later on.