Crown moulding on a radius
You cannot bend an existing crown moulding to a curve. The top and bottom edges need to bend at different radii and that is not possible.
There are two ways to come up with curved crown out of wood. One is to build up a block that conforms to the curve of the wall and profile the face at the appropriate angle.
The other way is to take existing straight crown and glue a triangular strip on the back of two pieces to create a solid triangular crown moulding (i.e., you are filling the air space behind the installed crown with wood). You then resaw approx 1/4" thick strips out of each blank, alternating the position of the saw kerf to get one complete moulding out of the two. It is very time consuming, and usually needs a lot of glue and nails to pull together during installation. This method has been documented numerous times in publication such as Fine Homebuilding.
We use a company that molds the crown using plastic. We give them the radius and they have silicone molds for most poplar crown details. They pour the plastic into the mold, and it has straight legs to allow the straight molding to transition into the curved molding easily. Obviously, this is only for paint grade.
Slice and dice is the most straightforward method for paint grade. Otherwise it can be made as a true radius crown. It doesn't take much of a curve to twist flat crown.
I believe Flextrim makes a crown moulding that would be applicable to your project I have used 2-1/4" wm 356 on a 3' diameter with a little trouble with twisting, but when an adhesive was applied, it stayed perfectly.
The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).
Comment from contributor A:
Comment from contributor B:
How about not installing a wood crown mould, but plastering one in? Build a form to slide along the wall and ceiling that is a copy of the crown moulding intalled on the walls that are straight. Pack the curved section with scrap lumber. Pack plaster over the scraps and drag the template along the wall and ceiling. After a few passes you have crown moulding.
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