Step 1: Measure Your Radius and Pick a Method
Everything starts with the radius of your curve. For a curved wall, measure from the center point of the arc to the wall face. For an archway, the radius is usually half the width of the opening if it's a full half-circle, or larger if it's a shallow eyebrow arch.
The Gypsum Association publishes bending limits for gypsum board, and the numbers are worth writing down. Their technical guidance on using gypsum board for walls and ceilings covers curved applications in detail. The short version:
Dry bending: 1/2 inch board handles about a 10 foot radius. 3/8 inch gets down to roughly 7.5 feet. 1/4 inch manages around 5 feet.
Wet bending roughly cuts those numbers in half or better. Dampened 1/4 inch board can wrap a radius close to 2 feet.
Anything tighter than that, you're into flexible drywall (a special 1/4 inch product made for curves) or the scoring method. Match your measured radius against those limits and you know which approach you need before you buy anything.
Step 2: Get the Framing Right First
Flat walls hide framing sins. Curves expose every single one. On a standard wall, studs sit 16 inches on center and the stiffness of the drywall bridges between them. On a curve, the drywall is already stressed from bending, and wide framing gaps let it flatten out between supports. The result is a curve with visible flat spots, and no amount of mud fixes that.
Frame curved sections with supports every 6 to 9 inches on center. The tighter the curve, the closer the spacing. For an archway, that usually means cutting a pair of curved plywood templates for the sides, then running short blocks between them every few inches along the underside of the arch.
Run your hand along the framing before you hang anything. High blocks and proud screws telegraph through thin board much worse than they do through 1/2 inch. Ten minutes with a rasp here saves an hour of frustration later.
Step 3: Bend the Board
You've got three options depending on how tight the curve is. I've used all three, and each one has a spot where it's clearly the right call.
Dry Bending for Gentle Curves
If your radius is generous enough for the thickness you're using, just bend it in place. Start screwing at one end of the curve and work across, pulling the sheet tight to each support as you go. Never fasten both ends first and push the middle in. The board needs to take the curve progressively. Two layers of 1/4 inch board, with staggered seams, gives you the same finished thickness as single 1/2 inch and bends far more willingly.
Wet Bending for Tighter Curves
Water is the old plasterer's trick. Spray or sponge water onto the face and back of the board (the compression side matters most), then stack it curve-side up over a form or just let it rest for 30 to 45 minutes. The gypsum core softens and the board gets noticeably floppy. Bend it slowly onto the framing, screw it off, and let it dry completely before taping. Drying takes a day or more depending on humidity. The board regains its full hardness once dry. My mistake the first time: too much water. The face paper started to bubble and the core got mushy at one edge. Damp, not soaked.
Scoring for Tight Arches
For the underside of a tight archway, score the back of a drywall strip every inch or so across its width, cutting through the back paper and partway into the core. The strip then snaps into a series of small facets that follow the curve like segments on a watch band. Screw each facet to the arch framing. Yes, it looks rough and faceted at this stage. Setting compound fills the facets in the finishing step and the cured result reads as a smooth curve. This is how I ended up fixing my sister-in-law's arch, and the patch is still invisible eight years later.
Step 4: Bead the Curved Edges
The edge where the arch face meets the curved underside needs corner bead, and standard metal bead does not want to follow a curve. You can snip the flange every inch and bend metal bead around, but every snip is a chance for a kink, and I've never gotten a result I loved that way.
Flexible vinyl archway bead is the answer. One flange is segmented from the factory so it fans around the curve while the nose stays continuous and clean. It runs about $10 to $15 per stick at the big box stores, which stung a little until I saw how much faster it went on. Attach it with staples or spray adhesive per the package directions, keep the nose aligned as you work around the arc, and check the curve by eye from a few steps back before you mud it.
Step 5: Finish With Setting Compound
Curved surfaces get finished the same way as flat ones, with two adjustments. First, use setting-type compound (the bagged stuff like Durabond or Easy Sand) for the fill coats, especially over scored facets or segmented bead. It shrinks less and builds thickness without cracking. Second, throw away your straight edge instincts. A wide knife spans a curve and gouges the high points, so I switch to a 6 inch knife and more passes, letting my hand follow the arc.
Check your work with a light held at a low angle across the curve. Flat spots and facet ridges jump out under raking light and stay invisible under ceiling light, right up until the afternoon sun hits the wall after you've painted. Sand lightly between coats, prime, and the curve should read as one smooth sweep.
Total cost for my archway repair came to about $70: one sheet of 1/4 inch flexible board, two sticks of vinyl archway bead, and a bag of Easy Sand 45. The afternoon project took two days with drying time. Plan for that and you'll be fine.