To ensure that molded products will release smoothly from the mold, a mold release agent is used. This release agent must be removed prior to priming and painting.
To remove mold release agent simply wash the ceiling medallion or door pediment in warm, soapy water and let dry. It is recommended that the surface of your decorative element be scuffed lightly with fine sandpaper to allow the prime to get a firm "bite".
After scuffing, remove dust with tackcloth or dusting brush and prime with oil or latex primer. After primer is dry, paint the ceiling medallion or door pediment in the color of your choice.
Since they are lightweight, ceiling medallions and door pediments do not require extensive fastening. The most solid fastening method is the use of several sheetrock screws fastened through the medallion and into the ceiling joists. Medallions and door pediments may also be installed using finish nails and adhesive such as Liquid Nails or vinyl trim adhesive. After adhesive drys you may want to run a bead of paintable latex caulk around the edge to seal any gaps.