How to Properly Cut Molding

Though not vital to the building structure, decorative molding plays a key role in completing a room’s aesthetic. It can add both value and protection to your home while giving it a polished, finished look.

Different types of molding serve various functions. Some moldings frame doors and windows, while others line the edges of rooms. At the bottom of walls, where they meet the floor, baseboards (also known as wall boards), shoe molding, and quarter-round trim cover the ends of the flooring. Chair rail molding, placed in the middle of the wall, helps protect the walls from chair damage. Crown molding covers the junction between the ceiling and the walls.

Molding pieces are commonly joined in three main ways: scarf or spliced joints, coped joints, and mitered joints. Scarf joints connect two pieces end-to-end, typically cut at 45-degree angles to create an overlap. Coped and mitered joints are designed for a smooth, clean finish when two walls meet at corners [source: Anderson].

As the saying goes, the devil is in the details, and when it comes to molding, the details are in the corners. Coping, which is often used for inside corners, involves carefully trimming part of the molding for a snug fit. Mitering requires exact measurements and cuts to ensure the two pieces of molding fit perfectly together [source: Charles and Hudson].

Think about the angles where two perpendicular walls intersect. The angle formed should either be 90 degrees (for an inside corner) or 270 degrees for an outside corner. To make the molding pieces fit into these corners, you’ll need to cut each piece at 45 degrees for an internal corner, and 135 degrees for an external corner.

Keep in mind that most corners are not perfectly 90 degrees. While baseboards, quarter nose, and chair rail moldings rest flat against the wall, crown molding is different and requires more precision in cutting to achieve the correct fit.

Continue reading to discover why it’s essential to measure your molding before making any cuts.

Measuring Molding Prior to Cutting

Start by measuring the area where the molding will be installed. Molding usually comes in 8-foot (2.4-meter) lengths, although 10-foot or 12-foot (3- or 3.7-meter) options are also available, so it's essential to select your molding before calculating how much you'll need.

When measuring, remember to round up. For molding that will encircle the room's perimeter, round all measurements to the nearest larger foot to account for cutting and adjustments. For instance, if one wall measures 8'3", round up to 9 feet (2.7 meters) when doing your math [source: Royal Mouldings].

Be as accurate as possible with your measurements, then divide the total by the molding's length and add 10 percent extra to cover potential cutting mistakes [source: Stimpson].

Take precise measurements of each corner's wall angle to calculate the right miter angle. Some wall angles may be less than perfect. It's not uncommon for walls that are supposed to meet at 90 degrees to be off by up to 3 degrees. While this may seem minor, it can result in a noticeable gap between the molding pieces if not considered before cutting, requiring a re-cut.

Before making any cuts, it's a good idea to measure twice and test the angles on scrap molding pieces. When dealing with corners, measure the shortest side of the molding needed for the cut. For inside corners, the top of the molding will be shorter; for outside corners, the bottom will be shorter. Be sure to measure again before making the final cut [source: Louisiana Pacific].

If two molding pieces are nearly fitting together, you can use acrylic caulk to seal any small gaps. A coat of paint can also help to make those gaps less noticeable [source: Anderson].

Cutting molding at an angle can be tricky. Learn the proper technique on the next page.

How to Cut Molding on an Angle

Before making your first cut, there are several important factors to consider.

What type of trim are you cutting? Different trims require different positioning in the miter box or on the saw:

Which piece are you cutting? Each molding joint has both a left and a right side. For a left-hand cut, most of the molding will be to the left of the blade (when the finished side is facing up, with the bottom down). For a right-hand cut in the same position, you're cutting the right side of the joint [source: Royal Mouldings].

What type of joint are you cutting? Spliced joints require 45-degree cuts. Coping joints need both a 90-degree and a 45-degree cut. Mitering can offer more precise cuts depending on the tool used. Since crown molding is installed at an angle to the wall, the angle of the molding must be taken into account. Detailed charts are available that specify the correct bevel and miter angles for the saw, depending on the angles of the walls [source: DEWALT].

To discover the essential tools needed for cutting molding, keep reading.

Essential Tools for Cutting Molding

Here’s a list of some of the tools you'll need to cut molding. The specific tools you need may vary depending on your project and the depth of the molding, so you might require additional tools based on the details of your task:

You'll also need a few additional items, such as glue; some professionals suggest using glue to join molding pieces before installation. If you plan on using the coping method to join molding, a coping saw is essential. For cutting 45- or 90-degree angles, you may need a miter box and handsaw.

To figure out the angle formed by the walls, you'll need an angle gage or a 360-degree adjustable protractor. A power miter or compound miter saw will give you more flexibility in adjusting angles, some for both the miter and the bevel. Choose one that has a carbide saw blade with at least 80 teeth. Ensure that the saw is square and that the table angle gage is precise. Even a 3-degree misalignment could result in a noticeable gap in the miter joint. An angled filler strip fills the space behind crown molding and is nailed to the horizontal wall plate behind the drywall, just under the ceiling. Use this strip to secure the crown molding in place. Finally, using some spray furniture polish can help lubricate the saw blade and make cutting smoother [source: Royal Mouldings, Carter, Anderson, Louisiana Pacific].

Now that you're prepared for your molding project and know how to cut it correctly, you’re all set. However, if you have any remaining questions, feel free to check out some of the helpful links on the following page.