Drywall/Plaster Hack

I’m in the middle of a DIY renovation to my old house. The original portion of the home has lath board and plaster, with a radius cornice where the wall meets the ceiling.



I recently closed in the old porch to create an entry room and took down the wall separating it from the old living room, and have been trying to figure out how I can make the transition from the new to the old as indistinguishable as possible.

One of the big challenges is to duplicate the radius cornice in the new room and have it transition into the old. As you can see in the photo of a piece of the cornice I removed when I took down the old wall, the original took a curved piece of metal lath and troweled plaster on top of that to get the radius.





With the max buildup being about 1-1/2”, I figured if I taped the corner, then did one initial build up of Durabond, left to set, followed by a second build up that was spritzed with water and passed over with a running mold I made to match the old radius (see gif below), I could get most of the way there. Then all that would be left was a thin skim coat or two with air drying mud, texture, and paint.



I’m trying a test run in a closet, and while it’s a huge pain in the arse, it’s coming out pretty nice. My only concern now is if that build up of Durabond will ever crack, but the shite is hard as a rock, so I’m optimistic. Any other thoughts/insight that might help once I’m out of the closet?