A reader wants to know how to repair the crown molding in a dining room ceiling. (Reader photo)

This story has been updated.

Q: Our plumber had to cut two holes in our dining room ceiling and remove a section of original cast-plaster crown molding to assess, access and make repairs to the second-floor bathroom plumbing above. Although I'm thankful we won't have to pull up any of the near-perfect 1913 hexagonal bathroom floor tile, I have no idea where to go for replacement molding. Does it look like this is a "stock" design? Will we need to have a mold and molding custom-made, or is this something we could do ourselves? Would it make sense to repair other areas of water damage in the room at the same time?

Washington

A: The plaster molding in your dining room wasn’t cast separately and put up in sections. The pictures you sent show that it was run in place, meaning a plasterer pushed in the shape by running a template with the opposite shape against wet plaster.

The molding and ceiling can be patched in an authentic way to look good as new, but it isn’t cheap. One reason is that even a small repair is time-consuming. Another is that there aren’t many people who still know how to do it. One who does is Reggie Bullard, who has nearly a half-century of experience as a plasterer and does interior and exterior work throughout the D.C. area through his company, R.T. Bullard in Woodbridge, Va. (703-845-1565; rtbullard.com ).

Bullard said he would first assess the situation. Then he could answer your question about whether it would make sense to repair other areas of water damage at the same time. Plaster lasts essentially forever if it stays dry, but water can make it crumbly and loose. He would need to figure out whether the other areas are just stained or are disintegrating.

To replicate the missing sections of molding, he would need to copy the shape, then cut a mating profile in stiff metal. After filing the edge for a perfect fit, he’d outfit the blade with wooden stiffeners and a bottom piece, called a sled, that he could slide against a straight guide screwed to the wall, underneath the existing molding.

He’d patch the ceiling first, aiming to create a perfectly level surface. “You need a true plane,” he said. He often has to enlarge ceiling holes by another foot or so to get a large enough area for a smooth, level patch. A difference of more than one-sixteenth of an inch from the surrounding ceiling would be noticeable.

Although older plaster was typically backed up by thin wooden slats called laths, Bullard often fills in behind with metal laths. Then he spreads on layers of molding plaster. It stiffens quickly, often in 10 or 15 minutes, so he can do multiple coats. But there’s little opportunity to go back and fix details if they don’t turn out right the first time. The plaster dries hard; any unevenness can’t be sanded smooth afterward, unlike drywall mud.

Bullard estimated that it would cost about $4,000 to repair each of the holes shown in the pictures you sent. D.L. Boyd in Hyattsville, Md. (800-383-0137; dlboyd.net ), which also does plaster repairs, offered a similar estimate: $5,500. For estimates from either company, of course, you would need to arrange for someone to visit your house.

Given the cost of doing the repairs in an authentic way, you might be tempted to do the work yourself or search for other patching options. There are YouTube videos on how to patch plaster crown, but unless you are especially talented, it might not turn out well. Bullard said the do-it-yourself patches he’s seen look “like you let kids come in and do it with Play-Doh.”

He is similarly dismissive about attempting to patch the molding with a piece of ready-made molding, either plastic types such as those made of polystyrene foam or ones cast from glass-fiber-reinforced gypsum plaster. Bullard said these usually come out looking “like sausage links” butted together.

Still, if you don’t have thousands of dollars for repairs, you might be able to patch in pieces that leave your dining room better-looking than it is now and perhaps almost as good as new. RWM in Murray, Utah, (801-268-2400; rwm-inc.com ) replicates crown molding and other plaster details using glass-fiber-reinforced gypsum plaster. The fibers make the pieces strong enough to ship cross-country.

You or a contractor would need to cut out a full-width section four or five inches long of each style of molding, or you could extend the existing saw cuts to get a full-width edge or slot where you could slip in a piece of poster board to trace the profile. From that, RWM would make a custom mold, form the lengths you need and mail them to you. Owner Dan Litson estimated the cost at $1,300 plus shipping if you have a single molding profile, as he thinks you might. If you’d need two molds, add $550. The estimate is based on a guess of four feet of molding for one hole and two feet for the other; it also includes crating the pieces for shipping. Experienced drywall contractors who have tackled a variety of remodeling jobs typically have the know-how to clean out the holes, patch the ceiling, install the molding sections and smooth over joints. Litson says RWM can offer installation advice, if needed.

Just don’t ask the plumber to handle any aspect of the repair. It’s too late now, but it’s possible that you could have avoided much of the damage if you had called in someone with a restoration mind-set to make the initial cuts. A remodeling contractor or a plasterer might have tried cutting just through the ceiling to see if that access was enough. Or they might have sliced out the molding in one piece, so it could be reinstalled later or at least used for creating a template or mold. When plumbers cut through walls or other surfaces, the holes often aren’t pretty.