Q&A / 

Installing Drywall In Wet Locations

DEAR TIM: My church group is restoring a house and all of the walls and ceilings in the bathroom and laundry area have been stripped down to the wall studs. How much water-resistant drywall should we install? Is it best to use it just behind the plumbing fixtures and appliances or should all of the walls and ceiling be covered? John G., Detroit, MI

DEAR JOHN: There seems to be a significant amount of confusion about drywall, water-resistant drywall and wall board that is 100-percent waterproof. Since you are in the driver's seat at this time and have a choice of what material to use, you can produce a finished result that should last for many years with little or no damage if an occasional splash or drip occur or even if lots of water floods a wall surface.

Drywall that most people are familiar with is made with a gypsum-based core that is very strong when it is dry. Typically the drywall panels have a thick-paper wrapping that protects the gypsum core from impact and abrasion damage. But the paper readily absorbs water and can transmit it to the gypsum inside the panel. When this happens, the panel loses its rigidity and either falls apart or it becomes very mushy.

The drywall used around this utility sink should have been the special water-resistant drywall. Instead, the homeowner has had to initiate damage control by sealing the peeling-paint spots on the wall with clear urethane. PHOTO BY: Tim Carter

The drywall used around this utility sink should have been the special water-resistant drywall. Instead, the homeowner has had to initiate damage control by sealing the peeling-paint spots on the wall with clear urethane. PHOTO BY: Tim Carter

With this in mind, I don't like to use regular drywall in areas where I think water might come into contact with the wall surface on a regular or even somewhat-regular basis. Some people think that several coats of high-quality paint will protect the drywall from moisture, but this is not always the best strategy. If water gets behind the paint where the paint stops and a sink top or cabinet edge begins, you have an Achilles' heel and damage to the drywall may start if water finds this entry point from time to time.

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Water-resistant drywall has been around for over 25 years. Many people recognize it from the green-colored paper facing. In fact, it is affectionately called green board by builders and drywall hangers. It is a great product when it is used exactly as it was designed to be used.

For example, I have had great success using this green board drywall behind sinks, toilets and on walls with ceramic tile back splashes. But I have had horrific failures when I have used it behind ceramic tile in tub and shower areas. Water and water vapor can readily pass through ceramic tile grout and cause the paper facing of the drywall to disintegrate. Water-resistant drywall is simply not recommended for areas that are subject to constant moisture.

The water-resistant green board drywall also is sensitive to stud spacing. If you decide to use the green board drywall for a ceiling, the joists must be spaced 12 inches on center for 1/2 inch thick drywall. If you have 16 inch on center spacing, then you need to increase the thickness of the drywall to 5/8 inch for ceilings.

Some drywall manufacturers also state that a vapor retarder should not be used under the water-resistant drywall if the visible face of the drywall is covered by a product such as ceramic tile or other water-vapor impervious finish. I believe they are very afraid that water might get trapped within the drywall and cause damage.

In areas of these rooms that will get heavy concentrations of water, you need to use a waterproof wall material. Remember, the green board drywall is water-resistant, not waterproof. You can purchase interior panels that match the thickness of regular and water-resistant drywall that are made with cement and sand or a combination of cement, sand and other ingredients.

Furthermore, there are other innovative gypsum core products that are 100 percent waterproof. Use the waterproof wall panels behind tile and in any location where you expect water to be regularly splashed onto a wall surface.

Be sure to use hot-dipped galvanized fasteners or even stainless steel nails and screws to fasten the wall panels to the wall studs and ceiling joists. If you use raw steel fasteners, they will rust in time and the wall panels can fall off the walls or ceilings. At the very least, you will find yourself dealing with unsightly rust stains that appear through the painted surfaces should you cut corners and use the wrong fasteners.

The gypsum core of the water-resistant panels is often treated with a silicone chemical or wax-like substance. You can readily see water bead up if you wet the exposed gypsum core. The problem for years was the failure of the green-colored paper, not the actual gypsum inner core.

Because mold is in the forefront of the news, wall and ceiling panel manufacturers are constantly rolling out products that are both water-resistant and even inhibit the growth of mold on the surface of the panel. But as with any new product, always be sure to read the technical literature produced by the manufacturer.

Make sure you use the product as it was designed to be used. Always pay attention to the use of the words: water-resistant and waterproof. Waterproof means liquid water or water vapor will not harm the product. Water-resistant means limited amounts of water will not cause harm.


18 Responses to Installing Drywall In Wet Locations

  1. My husband and I were originally going to install a shower kit, but have since changed our minds and want to do a tile shower.
    The thing is, we've already installed, mudded and sanded the green board drywall...is there nothing we can do (like cover it with something) or are we going to have to rip it out (where the shower will be) and install a waterproof wall material?
    Thanks so much!

    • Miriam, your question requires lots of typing, plus I have some questions for you so I can give you the correct answer(s). I only do pithy answers here in the comment section. If you want to protect the investment you have in your house and not waste time or money *hoping* you make the right decision, you should talk to me on the phone for just 15 minutes. It'll be the best investment you've ever made in your home!

    • You people should do some FREE research yourselves. You all sound so incapable. For WET areas such as tubs and showers...USE CEMENT BOARD.

  2. I have the exact same question as her so you could call me as well? Lol. I'm terrified they have me the wrong answer.

  3. Our condo apartment is adjacent to a common laundry room and four times in the last four years it has flooded due to a faulty washing machine. They will not fix the breach in the wall so how and what products can I use to stop the water from penetrating the wall into my unit. I have had to tear up the padding and carpet and am afraid to replace it with anything until I can figure out a way to seal up the concrete.

  4. Thanks for the article. Since green board is not suitable, what *would* you use behind a glue-on acrylic tub surround? thanks, -nikita

  5. I have to do an inexpensive tube job. What backing would you use in tub area, to go under sheets of FRP and glue

  6. What a great article you have introduced with us. Really inspiring. It is commonly the result of roofing and plumbing leaks. When walls are wet but haven’t been that way for more than a day, your best bet for reducing water damage is to allow air in from outside. Air circulation will help to make your walls dry faster than they would on their own.Thanks for great job .

  7. Hi Tim,

    My husband wants to use the greenboard product in our bedroom. Not because of moisture issues but just because. My question is....is it a safe product to use regarding health wise? What is it treated with to be mold resistant? Would one use it for entire home construction if they wanted to....cost not being an issue?

  8. I have a good question. I have a very big bathroom. Do I have to put the mold resistent drywall in the whole bathroom including ceiling or can I put it only where water might come in contact like the sink toliet and shower area.

  9. I have built a seasonal home on the Sunshine Coast,is green board a good product for my interior wall finishing ,considering the moisture content in the Winter,when there is no heat.

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