Everything You Need to Know About Drywall
Choosing the right drywall
To hang and finish drywall, you need drywall sheets, joint compound, tape, fasteners and edge treatments. That seems straightforward, but when you’re standing in the drywall aisle at the home center, the choices aren’t so simple.
In this story, we’ll walk you through the assortment of materials to help you make the right choices for your jobsite.
Is drywall fire-resistant?
“Type X” drywall is 5/8 in. thick and designed to slow the spread of fire. It is often required on garage walls and ceilings that adjoin living spaces, ceilings between living spaces inside the house, and under stairs.
Talk to your local building inspector to find out where and which kind of Type X is required. There are many varieties, each with a different fire rating. If you install the wrong type, an inspector can require you to tear it off and replace it.
Is drywall mold and moisture resistant?
Also called “greenboard”, mold-and-mildew-resistant 1/2-in. drywall is a somewhat different animal. Manufacturers use various methods to eliminate or treat the paper that covers the gypsum core. Getting rid of the organic paper food source was supposed to keep mold and mildew from growing. Builders used to install it in wet and damp locations, placing it behind tile in shower and bath enclosures. Those enclosures have already been or soon will be replaced as the greenboard fails.
Pro Tip: Although you’ll still find greenboard at home centers, we advise against using it, especially for tile backing in wet areas. There are much better alternatives for tile in wet locations—cement board, for one.
1/2-in. drywall is the best choice for most walls and some ceilings. There are standard and lightweight versions. Lightweight is stronger and weighs 25 percent less.
Pro Tip: Spend a few extra bucks and get “ultralight” or “lightweight” drywall. It is easier to handle and stiffer, so it can cover ceilings that have joists spaced at 24 in. That’s why some stores no longer even carry standard 1/2-in. drywall.
3/8-in. and ¼-in. drywall
If you’re doing repairs in a house that was built in the ‘50s or ‘60s, you may very well have 3/8-in. drywall. You’ll want to match that thickness to patch an existing wall. Measure the existing drywall or take off a switch plate cover to find out.
Pro Tip: Unless you’re matching existing drywall, there’s rarely a good reason to use 3/8-in. drywall. Remember that window and doorjambs are generally sized to be flush with 1/2-in. drywall.
1/4-in. drywall is a very thin material so it is mostly used to cover bad walls: cracked plaster or unremovable wallpaper, for example. Because it is more flexible, it is also sometimes used on arches or applied in two layers on curved walls. Specialty stores carry drywall that’s super bendable—flexible enough to drywall the inside of a barrel!
Pro Tip: Screws don’t countersink well in 1/4-in. drywall, so construction adhesive is a better choice if you’re covering bad surfaces. Tack it in place with a few nails until the adhesive sets.
All-purpose compound contains a lot of adhesive, making it the hardest, strongest type of drying compound. That strength makes it a good choice for the first coat (when you embed paper tape). You can use it for following coats too, but sanding will give you a workout.
The main advantage of lightweight mud is that it is easier to sand. The downside is that it is not as hard or strong, so it is a bit more likely to dent when bumped or to crack at joints. Look for the term “lightweight” on the label. Don’t use lightweight compound to embed mesh joint tape; that combination sometimes leads to cracks.
Setting compound is a powder that you mix with water just before use. It hardens by chemical reaction rather than by drying. The working time is usually the number that’s in the name. Besides hardening fast and allowing you to apply the next coat sooner, setting compound has three advantages over other joint compounds: It is harder, stronger, and shrinks much less. Setting compound is perfect for filling larger holes and bedding tape, but its’ much harder to sand, so it should be should never be used as a last coat.
Regular setting compound
This compound is very hard, very strong—and almost impossible to sand.
Lightweight setting compound
Lightweight versions sacrifice a little toughness but are much easier to sand than regular setting compound.
When it comes to drywall there are three main types of tape. First is paper tape. Paper tape is cheap and, surprisingly, stronger than fiberglass tape. And unlike fiberglass tape, it is pre-creased in the middle so you can fold it to tape inside corners. However, it takes a bit more skill to embed it in drywall seams.
The second main type of tape is fiberglass mesh. Mesh is far easier to use than paper. It has adhesive on one side; you just stick it to the wall and mud over it. Mesh tape is super forgiving for first-time tapers. But you’ll still have to use paper tape or reinforced paper tape for corners at wall-to-wall and wall-to-ceiling joints. Since it is not as crack resistant as paper tape, setting compound (standard or lightweight) is usually recommended for embedding mesh tape.
Reinforced Paper Tape
The third and final tape type is reinforced paper tape. Designed for inside corners and wall-to-ceiling angles, reinforced paper tape has plastic or metal strips on the back. They don’t make the joint stronger, but they do provide a stiff guide for your knife, making it easy to keep corners straight.
Choose drywall screws rather than nails—nails are far more likely to work loose and cause ugly craters or “pops.” The screw length depends on the drywall thickness: 1-5/8-in. screws are for 5/8-in. drywall; 1-1/4-in. screws are for anything thinner. Coarse threads are for wood studs; fine threads for steel studs.
You’ll find drywall screws with thin (No. 6) and thick (No. 8) shanks. Choose the thin ones. Thick-shank screws are harder to drive, break out drywall near edges and leave shredded paper around the screw head.
Edge and Corner Beads
Whenever drywall meets another surface like stone, brick or paneling, you need a neat way to finish the edge. You can always use wood trim, but there are some other options.
You have many choices for outside corners: metal or vinyl, square or bullnose, even bead for non-90-degree corners or arches. The big difference is how they’re installed. Standard metal can be nailed on and then taped; vinyl corner bead should be applied with special adhesive and staples. Paper-faced versions get “glued” into place with joint compound.
Pro Tips: Choose metal corner bead instead of vinyl or paper-faced bead. It’s easier to install and requires only ordinary tools. Exception: In damp areas like bathrooms and spas, vinyl is a good, rust-proof choice.
For our full story on all things corner bead, click here. Also, check out this video explaining the pros and cons of the four main corner bead types:
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