Everything You Need To Cast Plaster Details

Where> Boston What> Duplicated his home’s architectural details with molds It’s no secret that TOH readers have a weakness for restoring antique architecture—and Kevin Shale is no exception. He was thrilled that some of the original plaster corbels and ceiling medallions on the first floor of his crumbling 1877 brick townhouse had survived. Hoping to match those details throughout his house, Kevin taught himself how to reproduce the prized pieces. Here, find out what he used to prep the originals, create molds, and cast perfect copies so that you can do the same.

Rubber Gloves

Release Agent

Peel off old layers of paint from the original ornament after soaking it in warm water. Let dry, then prep the piece with this coating so that you can easily remove the mold once it hardens. $19 per quart; Abatron

Mold Paste

Kevin used Abatron’s two-part MasterMold to create reusable rubber molds of his originals. To support the molds after they dried, he set them in wood frames filled with plaster. Master-Mold, $54 per quart; Abatron

Paintbrush

Apply everything from the release agent to the mold paste with an inexpensive natural-bristle brush. $2; at hardware stores

Putty Knife

Once you’ve brushed on the initial coat of MasterMold, build up thicker layers with this tool. $2; at hardware stores

Tennis Ball

When casting a medallion, Kevin recommends placing one of these in the center hole so that it stays open. $2.30 for a can of three; Kmart

Plaster

After coating the inside of the mold with release agent, fill with a thin, soupy mixture of Plaster of Paris and water. Once it dries, peel off the mold. When you install the cast detail, use joint compound to fill any gaps between it and the ceiling or wall. Plaster of Paris, $6.50 for 4 pounds; Home Depot

Vaseline and Caulk

For reproducing small details, coat the original with Vaseline, then cover it with a thick layer of 100 percent silicone sealant. Let it cure, remove the mold, and fill with plaster of paris. Vaseline, $5 for 13 ounces; at drugstores. Caulk, $6 for 10 ounces; Lowes