If you're new to cutting and installing trim molding, baseboard is usually the best type to start with. Baseboard is easy to install because it runs along the floor and sits flat against the wall, unlike crown molding, which sits at an angle at the union of walls and ceilings. A baseboard treatment may consist of single-piece molding, with either a flat or profiled face or edges, or it can be a "built-up" treatment made with multiple pieces—such as a main baseboard with a separately installed decorative cap trim along the top of the baseboard and a base shoe molding running along the bottom. Once you master the ability to cut and install baseboards, other trim moldings are relatively easy to install, since the same techniques are used.
Baseboard Molding Joints
A baseboard installation usually requires two or more different types of cuts for the different corner joints where the mating pieces meet. On inside corners, where the molding meets at the inside of wall corners, you can cut the baseboard with square ends only if the molding is flat-faced and has no profiled edge. If the molding is profiled or contoured, you must use either a mitered joint or a coped joint. A mitered joint is made with two pieces cut at 45 degrees to form each half of the 90-degree angle. A coped joint involves square-cutting the first piece of molding, then shaping or "coping" the second piece with a coping saw to fit against the contoured face of the first piece.
On outside corners, where the molding meets at an outside, or protruding, wall corner, it almost always looks best to use a mitered joint. Here, both pieces of molding are cut at 45 degrees (as with an inside miter), but the angles are cut in the opposite direction from an inside-corner mitered joint.
If a wall is longer than a full piece of baseboard, use a scarf joint to join the pieces for a seamless look. To make a scarf joint, cut a 30- or 45-degree miter on the first piece so the end of the board tapers toward the wall. Then, you cut the same angle on the second piece—with the miter facing in the opposite direction from the first—and overlap the second piece over the first. Scarf joints are typically much less visible than butt joints since natural contraction and expansion does not open up visible gaps between pieces of molding.
The best tool for cutting baseboard and related moldings is a power miter saw, but you can also use an inexpensive miter box and a small, rigid handsaw called a backsaw. The backsaw fits into the slots of the miter box to cut accurate angles and miters at 45 and 90 degrees.
Things You'll Need
Power miter saw or miter box and backsaw
Hammer or nail gun
Coping saw (optional)
Nail set (optional)
How to Install Baseboard Molding
Step 1: Mark the Wall Stud Locations
Use a stud finder to locate the wall studs in the installation area. Mark the center of each stud with a short pencil line, just above the where the top of the baseboard will fall when it is installed. These reference marks will let you see where the studs are located when you nail the baseboard.
Step 2: Cut the First Molding Piece
Measure between the two opposing walls for the first piece of baseboard. Cut the first piece of molding to the measured length. If you are making mitered corner joints, miter-cut both ends of the piece at 45 degrees. If you are making coped joints, cut the ends square.
If the wall is too long for one piece of molding—requiring a scarf joint where the two pieces will meet in the center—measure from the starting inside corner to the center of a stud near the center of the wall, then add about 1/4 inch.
Step 3: Install the First Piece
Set the cut baseboard in place so it is flush against the floor and fits tightly into the wall corner(s). Starting near the center of the board's length, nail through the baseboard and into the center of a wall stud, using a nail gun or a hammer and finish nail. Drive one nail near the top of the molding (choosing a flat area, if possible, rather than nailing into contours or decorative details) and one near the bottom; the bottom nail will likely drive into the horizontal bottom plate of the wall instead of the stud.
Continue nailing the baseboard at each stud, stopping about 2 to 3 feet from the ends of the board. This will allow you to make fine adjustments to the ends so the corner or scarf joints fit nicely.
Step 4: Cut and Install the Second Piece
Measure and cut the second piece of baseboard to length, using a 45-degree miter cut for the end that will meet the first piece. If you're making a coped joint, use a coping saw to cut along the profile of the molding, following the line of the miter cut and back-cutting at a 30- to 45-degree angle with the saw to create a crisp edge.
Fit the second piece of baseboard into place and line up the two pieces at the joint, then nail the second piece to the studs and bottom plate, as with the first baseboard. Complete the nailing of the first baseboard up to the joint.
Repeat the same process to install the remaining baseboards ending at inside corners.
Use a nail set and hammer to drive the heads of the finish nails slightly below the surface of the wood for a finished look.
Step 5: Complete the Outside Corners
For baseboard pieces fitting on outside corners, mark the baseboard in place rather than measuring. Make the inside-corner or scarf-joint cut first, then position the position the piece against the wall so it extends past the outside corner. Mark the top edge of the piece where it intersects the wall corner. This mark indicates where the miter will start (called the "short point" of the miter). Cut the piece at 45 degrees so the point of the cut edge will extend past the wall corner.
Cut the mating piece of baseboard using the same technique. Position both mating pieces on the wall and check the fit of the miter joint at the outside corner. Nail both pieces in place, starting at the outside corner and working toward the opposite end of each piece.
Step 6: Install Additional Moldings
If you're adding a decorative cap molding, cut and fit each piece using the same techniques used for the main baseboard. Install the cap molding with small finish nails, driving the nails into the baseboard or the wall studs, as appropriate.
Install base shoe molding with mitered joints at all of the corners (coping base shoe usually isn't worth the trouble). Install the base shoe with small finish nails driven at an angle into the floor or subfloor. Because it's nailed into the floor instead of the baseboard, the base shoe won't move and show gaps if the baseboard shrinks with seasonal humidity changes. Base shoe is also flexible, so you can push it down to follow contours in the floor while you're nailing it, eliminating gaps.
Philip Schmidt is author of Install Your Own Solar Panels, The Complete Guide to Treehouses, and 18 other home-related how-to books. A former carpenter, he has been a full-time writer and editor for over two decades, teaching DIYers about houses and everything we do with them.