Lining and Attaching the Horizontal Top Rail
To help clarify the difference in wall covering terms, a dado cap rail sits on top of the top rail to finish off the project. But before the cap rail is installed, the wall covering must be in place. The first step is to attach the horizontal 6" top rail to the wall. Scribe a light pencil mark on the wall 1 1/2" below the proposed height of the cap rail. This wall mark represents the height of the top rail, typically between three and four feet up from the floor. To assist in attaching the horizontal top rail, a level pencil line must be drawn on the wall. Using a 6' level or laser level and a long straight edge, trace a horizontal line on the wall from corner to corner to help align the top rail placement. If covering more than one wall, continue the top rail pencil line all the way around to the end of the planned project.
Next, mark on the line or place a piece of blue painter's tape where the wall studs are located. To find studs, tap the wall with a knuckle, continually rapping horizontally across the wall. Listen for the difference in sound and feel as the tapping sound alternates from a hollow knock to one of solid connection.
Start from one end of the wall or door trim and attach the top rail using a finish nail gun to secure the first section of top rail, hitting the marked wall studs. This end section, which is usually against a wall or door trim, uses a 90-degree cut, or square cut with the miter saw. Use the wall pencil line and an assistant to guide the top rail placement.
Continue attaching the top rail to the wall corner. If the top rail incorporates more than one wall, wrap the inside corner by matching two 45-degree bevel cuts to create a clean 90-degree turn. Note: Most walls have a 90-degree turn, but not all, as at Blog Cabin 2011. Continue "wrapping" the top rail, following the pencil mark to the end.
Builder's Tip: This DIY project may require another set of hands at times. Holding the 6' level or long straightedge while marking pencil lines is easier with two DIYers working together.
Builder's Tip: Most often, a single piece of top rail will not reach from one side of the wall to the other. Therefore, two pieces must be installed on the wall, creating a seam, or scarf joint, between the two pieces. With today's modern miter saws a square cut for an in-line joint will suffice, but over time, wood shrinkage will create a gap between the two pieces. To avoid the visible gap and to "hide" the seam, a bevel cut with the miter saw is made. Set the wood flat on the saw base, rotate the saw blade 45 degrees and make the first cut. On the second piece of top rail, another 45-degree bevel cut will be made in order to "slip" the end underneath the first cut. To make this cut, the top rail piece must be turned upside down on the miter saw base. The two 45-degree bevel cuts at the seam's two ends now create a scarf joint. This cut minimizes the seam's appearance and eliminates a wood shrink "gap" after wood putty is applied.