Q: I’d like to add an arched entryway between the living room and kitchen. Can you tell me how to bend drywall for the arch?
A: Gypsum board, also known as drywall, can be used to form almost any cylindrically curved surface. According to the Gypsum Association, standard 1/2-inch drywall can be bent around curved framing to a radius as small as 10 feet, as long as the panels are installed with their long edges perpendicular to framing members that are spaced no more than 6 inches on center. The 5/8-inch panels can bend to a 15-foot radius; 3/8-inch panels to a 7-foot, 6-inch radius; 5/16-inch panels to a 6-foot, 3-inch radius; and 1/4-inch panels to a 5-foot radius. Drywall can be bent to tighter curves than listed above by wetting the paper backing, or wetting the front and back paper. Use a short-napped roller or hand mister to dampen the panel. Allow the panel to lay flat for at least an hour so the moisture can penetrate the gypsum core. Bend as needed, but be very careful—wet drywall is easy to damage. Upon drying, the panel will regain its original hardness. (Note: when wetting drywall, it is imperative to use plenty of airflow to dry the boards completely after installation.)
For very tight curves, you can also score the back of the panel width-wise to give it more flexibility. To do so, first cut the panel to size. Then use a utility knife to make parallel cuts from edge to edge, spacing them roughly 1 inch apart. Then break the core at the cuts to create a flexible length of drywall.
Aside from standard gypsum board, also available are special flexible panels that can bend to much tighter radii. These 1/4-inch panels are usually installed in double layers and can achieve a radius as small as 12 inches.
– Source: The Gypsum Association, www.gypsum.org