Casing is available in a variety of design styles and profile options, from square-edged designs to colonial-style molding. Rosette blocks, decorative squares that butt the casing pieces at the top corners of the door area a great Victorian-style option that eliminates the need to miter the ends of the trim.
Painting Before Installation
If you are using paint-grade door casing, you may want to paint the pieces before you cut to length and install. Use semi-gloss paint for door casing. Flat paint is harder to clean, and flat-painted casing will show any dirty fingerprints.
Door casing, or trim, finishes the look of a newly installed door or can update the style of an older doorway. Care must be taken when installing casing, as the main purpose is not decorative, it is functional. Casing conceals gaps between the door jamb and the rough opening. If you are installing a new door, the casing may come mounted on one side of a pre-hung door. If you choose to replace existing trim, you will need to remove it with a pry bar and a hammer.
Mark and cut the top piece to length, mitering each end. The most important part of installing door casing is making sure that you cut the miters so that they fit together at the corners. Some DIYers choose to install the top piece first, making sure it is level and on the mark, before installing each side piece. With the top in place, you can use the top miters to mark the side pieces. If you need to make adjustments, use a sanding sponge to gently remove material and shape the miter.