Unit 61 Interior Trim Wood Molding • Composite Molding • Trimming Door Openings • Trimming Window Openings • Installing Base Molding • Installing Ceiling Molding

Softwood and hardwood lumber are used in the manufacture of wood molding. When manufacturing molding from solid lumber, a strip of lumber is resawn into a blank, which is a piece that will produce the desired pattern of molding with the least amount of waste. See Figure 61‑1. The blank is shaped into molding on a machine called a molder (or sticker). The molder is equipped with cutter heads and knives that rotate at high speed to create the molding pattern. Computer-controlled molders are used in many mills and shops which produce large quantities of molding.

Wood moldings are trim pieces at the juncture of walls and ceilings and floor and walls, and at intersections of other materials. Typical wood moldings are designed for the intersection of ceilings and walls or walls and floors and for door and window openings, astragals on double doors, and handrails. See Figure 61-2.

Molding is commonly installed along the floor and around door and window openings. In some cases, ceiling molding is specified. A sequence of interior molding installation is shown in Figure 61-3.

Door casing patterns may be contemporary or traditional in design Door casing patterns may be contemporary or traditional in design. Door casing is usually backed out to produce a tight fit. Door casing is available in many designs. See Figure 61‑4. Casing material is usually backed out. Backing out the material gives the molding flexibility, and produces a tight fit even if there is unevenness between the jamb and the wall.

Door casing is nailed to the trimmer stud and side jamb. When nailed to the jamb, the casing should be held back 1/8″ to 3/16″ from the edge. This space is called a reveal. A reveal creates a better appearance and puts the casing out of the way of the door hinges. When tapered casing is used, the narrow edge is nailed to the jamb with 4d or 6d nails and the other edge to the wall studs with 8d nails. See Figure 61‑5.

A 45° miter cut is usually required at the joints between the top piece and the side pieces of door casing. A 45° miter is usually cut at the joints between the top piece and the side pieces of casing. See Figure 61‑6. When freehand cutting with a handsaw, the miter angle is laid out with a combination square. When several openings are to be trimmed, a power miter saw may be used to make accurate miter cuts. A job-built miter box may also be constructed to make accurate miter cuts.

When trimming a door opening, first mark the doorjamb at intervals for a 1/8″ reveal. If a miter joint between the head and side pieces of the casing does not fit properly, use a block plane to make a better fit. When nailing casing to a jamb, drive nails down from the top piece into the side pieces at the miter joint to prevent the joint from opening up later. Applying glue at the joint is also helpful. A procedure for trimming a traditional door opening is shown in Figure 61‑7.

More shrinkage occurs across the grain than along the grain of wood More shrinkage occurs across the grain than along the grain of wood. Since there is more width at the heel than at the toe of the miter, the heel of the miter joint opens up. As wood moldings dry out, the wood shrinks more across the grain than along the grain, pulling on the face of the miter. Also, since there is more width of the molding at the heel of the miter than at the toe of the miter, the angle of the miter increases and the heel opens up. See Figure 61-8. Miter joints for interior applications rarely open up at the heel unless there is excessive moisture in the building.

Specialty clamps may be used to apply pressure to a miter joint to allow the glued joint to reach its full strength. After the glue is applied, the miter joints are clamped tight with specialty clamps before the glue sets. See Figure 61-9. A glued joint will not reach its full strength unless pressure is applied to the joint. Nails or counterbored screws are used to secure the joint, and biscuits or splines may be used to reinforce the joint and align the faces of the trim pieces.

Interior window trim for wood-framed windows may be either contemporary or traditional in design. Window trim should match door trim in the building. Window casing should be the same material and design as door casing. Most wood-framed windows are trimmed in either contemporary (picture‑frame) or traditional style. See Figure 61‑10. Some types of windows have only a sill and apron to trim the opening; no casings are installed.

Traditional window trim requires a rabbeted stool Traditional window trim requires a rabbeted stool. A variety of patterns are available. Traditional-style windows require a rabbeted stool to be installed before the casing can be nailed in place. Some stool designs are shown in Figure 61‑11.

When a stool and apron are installed, a corner return is used to conceal the end grain. A procedure for trimming a traditional window is shown in Figure 61‑12. The stool and apron have a 45° miter joint at each end to make a corner return. A corner return covers the exposed grain on the end of the stool and apron.

Base molding is held tightly to the finished floor and nailed to the bottom plate and studs. Base molding (baseboard) is held tightly to the finished floor and fastened to the wall with 6d or 8d finish nails driven into the bottom plate and studs. Some baseboard patterns are shown in Figure 61‑13.

Base molding is usually thinner than the door casing it butts against. Base molding is installed after the door casing has been nailed in place. Base molding is usually thinner than the outside edge of the door casing it butts against. See Figure 61‑14.

Base molding may be applied with a base shoe and base cap. A base shoe may be nailed into the floor at the bottom of the base molding to help conceal any unevenness between the base and the floor. A decorative base cap may also be used if molding is traditional style. See Figure 61‑15.

For an inside corner fit, one piece of the base molding must be cut for proper fit. Miter joints are required at the outside corners of base molding but are not suitable for the inside corners. At the inside corners, miter joints tend to open when being nailed. Later shrinkage of the wood also may cause inside corner miter joints to open. For this reason, a coped joint is recommended for inside corners. One piece is coped to the shape of the piece it fits against. Figure 61‑16 shows a procedure for coping.

A scarf joint produces the best fit between two pieces of base molding joined along a wall. Scarf joints should always be glued to limit separation. On long walls where several pieces of baseboard are required, the joints between the pieces should fall over a stud. The best type of fit is a scarf joint, which is made by overlapping two 45° angles. See Figure 61‑17.

When fitting base molding, first fit and cope the inside corner of one piece, then miter the outside corners. A procedure for placing baseboard in a room with inside and outside corners is shown in Figure 61-18.

The three basic profiles of ceiling molding are rectangular with a beveled edge, cove, and crown. Ceiling molding is available in three basic shapes. A contemporary design is rectangular with beveled edges. Traditional profiles include crown and cove moldings. See Figure 61‑19.

When installing crown molding, one of the inside corner pieces is coped. The procedure for placing ceiling molding is similar to that for base molding. One piece of the inside corner is usually coped as shown in Figure 61‑20. The outside corners are mitered. A scarf joint is recommended for joints between pieces on longer walls. The pieces are attached to the wall with 6d or 8d finish nails driven into the wall studs.

When cutting a 45° angle on crown molding, position the molding with the bottom edge pressed against the fence of the miter box. The lower side of crown or cove molding fits against the wall. It has a wider surface than the top side, which rests against the ceiling. To cut the miters (45° angles) for outside corner joints, a different procedure is required. To cut the miter, mark the short side of the 45° angle and position the molding as though the fence of the back side of the miter box is the wall and the bottom of the miter box is the ceiling. See Figure 61‑21.