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Trim Tips for DIY’ers

Construction How-To, Molding, Trim Carpentry December 10, 2015 Sonia








Trimming out a room is a hot project for DIY homeowners who want to dramatically accent an otherwise lackluster ceiling, wall or window.

In addition to traditional baseboards, chair rails, crown molding and casing, homeowners can also consider options such as fireplace mantels, cornices, medallions and more.

Choice of Materials

MDF (medium-density fiberboard) is often the trim material of choice because it’s less expensive than solid wood. Trim pieces made from finger-jointed wood are widely used in remodeling applications because they don’t have knots and imperfections like solid pieces can have. Most home centers sell both MDF and finger-jointed trim pieces in factory-primed standard lengths. An experienced carpenter can also fashion unique moldings made from solid woods, such as mahogany, maple and poplar. Solid wood can be stained instead of painted to reveal the natural grain.


Urethane, composites and other synthetic materials are popular choices for paint-grade trim. Although the products cost more than wood trim, they don’t have the same maintenance problems and are suited for outdoor use. Synthetics and composites resist insects, cracking, peeling, chipping, swelling, splitting and rotting, making them ideal for exterior use—as well as areas exposed to moisture, such as base molding in a bathroom or crown above a shower.

Most paint-grade trim products are sold pre-primed. If your selection is not pre-primed, you might consider both priming and painting all the trim pieces before you install them. This will reduce the time you spend working on your knees (for baseboards) or a ladder (for crown molding) and limit your post-installation painting to touchup work.

Learning How to Cope

When installing baseboards, crown molding and chair rails, it’s tempting to cut 45-degree miters at the corners and hope for a sure fit. The problem is that most walls aren’t 90 degrees. Joining two 45-cut molding pieces may give you a square joint, but a square joint may not work for your crazy corner. This problem might be due to a framing error or a buildup of drywall compound in the corner. But even a perfect miter joint can develop gaps when the wood dries and contracts in winter.

Unlike miter joints, cope joints have one trim piece butted against the adjacent wall at the corner. The joining trim piece is carefully cut to nest against the profile of the first. These joints eliminate the problem of out-of-square corners when installing trim, and they’re less likely to reveal a gap when the wood shrinks.


To make a cope joint, butt the first piece of molding into the corner and fasten in place. The second piece of molding should be cut a few inches longer than its final length. On the intersecting end of the second piece, cut a 45-degree inside miter. Run a carpenter’s pencil along the edge of the mitered profile, marking the shapes and curves for better visibility.