Plaster moulding professionally installed runs $10 and up per lf in my area. So the main objection is that polystyrene/polyurethane mouldings are "cheap". (Though I wonder if most people could tell the difference without poking a piece with their finger.)

This post was edited by worthy on Thu, Jul 3, 14 at 16:16

Concerns are:

I never had any success cutting with anything other than my power miter saw(with an 80 tooth blade and slow speeds) or a hand coping saw. Used fine files for final shaping.

Stuff breaks very easily. Mandatory to have two installers minimum. Means two people to cut/carry/hold in place/nail. Three is even better.

Cutting to get good fits on corners. Cope cutting inside corners and miter cutting outside corners is the (IMHO) best method. Cutting foam is different from wood/MDF and requires a lot of attention.

Installing with nails. Hand nailing can create dents. Each nail should be started by hand and finished with a nail set. Very labor intensive. Nailing with an air nailer using too much pressure means a divot for each nail and the porbability the nail goes completely through the molding. But, any nail site will require putty. Smaller holes mean less/faster puttying.

Depending on the width of the crown, you might need a backer installed. Wood strip sized to be installed in the angle between wall and ceiling to support the crown and for nailing.

Foam crown is my third favorite, after painted wood and stained wood. Much better than MDF crown.

Thank you both. Not sure it is diy job after all!