This is very similar to one of my next projects. I will be replacing some custom stucco moldings surrounding some wood arch windows.
We will buy some 1" thick foam and use a router on a trammel to shape the face profile. Then band saw the arch out of the blank. Since it's exterior, most of the foam core molding material seems suspect to me. I think I need a high density foam that I can expose the core to paint.
Any ideas what to ask for?
The detail shown here is pretty close except we are making complete half rounds.
