Project level: Intermediate

Architectural moulding is a premium, polystyrene or polyurethane moulding with large profiles that mimic the look of built-up moulding. Architectural moulding will not warp, rot or split. It is a low maintenance material that saws, mills and works just like wood. It is lighter than hardwood for easier handling. The most important tool when working with moulding is patience. Never try to rush trim work. Lowe's is happy to provide this information as a service to you.

Tools and Materials

Tools

• Tape measure    
• Dropcloth
• Drill/driver    
• Dust mask
• Bits    
• Caulk gun
• Hammer*   
• Paintbrush or staining brush
• Level    
• Goggles
• Miter saw    
• Nail set*

 Materials

• Wood putty
• Moulding
• Stain or paint
• Nails*
• Caulk

*As an alternative, you can use adhesive to install architectural moulding. When using adhesive, you will not need a hammer, nail set or nails. Use only adhesive recommended by the manufacturer.     

Locating, Cutting and Fitting

• General

Start by cutting your moulding pieces a little long, you can always trim a little off, but once a piece is too short it can't be fixed.
Predrill holes for nails.
If you use a power miter saw, use at least a 60 tooth blade.
In order to establish a level line for a chair rail, measure up from the floor to where the bottom of the chair rail will be and make a mark. Use a level as a straight edge and lightly draw a line around the room. As you install the chair rail, make sure it is even with this line.

• Base and Chair Rail Corners

Lay the moulding with its back flat against the bottom of the miter box or the bed of the power miter saw. For inside corners, cut through the face at 45° so the edge of the cut is visible from the front. For outside corners, cut through the face at 45° so the edge of the cut is hidden from the front. Cut the pieces as mirrors to each other.

• Crown Corners

For architectural moulding there are premade inside and outside corners available. The simplest way to make nice crown corners is to use the manufactured corner blocks. If you choose not to use the premade corner blocks, use these guidelines for your crown moulding corners. For outside corners, use a power miter saw and set it as indicated in in our crown moulding adjustment table. For inside corners, you can either miter cut the pieces or cope them:

• To miter the pieces, place the moulding so its top (the part that goes against the ceiling) is flat against the bottom of the miter box or bed of the power miter saw. The bottom (the part that goes against the wall) should be flat against the side of the miter box or the power miter saw's fence. Cut the pieces as mirrors to each other on 45° angles.
• To cope the pieces, butt one piece tight against the wall and nail in place. Place the second piece in your miter box or power miter saw as described above and cut the piece at 45° so the edge of the cut is visible from the front. Use a coping saw to cut a slight back angle following the contour of the exposed moulding profile. Test fit the coped cut and trim as necessary. See the animation below for more information on coping moulding.

Splicing All Types of Moulding

When you are covering a span that is longer than your moulding, splice two pieces together with a scarf joint. Lay the moulding with its back flat against the bottom of the miter box or the bed of the power miter saw. On one piece, cut through the face at 45° so the edge of the cut is visible from the front. On the second piece, cut through the face at 45° so the edge of the cut is hidden from the front. The joint should meet over a wall stud or some other point where it can be nailed.

• Determine How Much Moulding You Need

1. Measure the room at the height where each moulding will go to determine the footage of moulding you need. Jot these measurements down. Keep separate measurements for base, chair rail and crown moulding.
2. Since architectural moulding usually comes in 8' lengths, divide your footage by eight and multiply that number by 1.1. The result is the total footage needed plus ten percent for waste. Perform this step for each type of moulding, base, chair rail and crown, separately.

• Apply the Finish

1. Apply the finish to the moulding before installing it. You'll save time because you can apply the finish faster. Find a dry, well-ventilated and dust-free area to apply the finish to your moulding.
2. Put down a dropcloth and apply the finish according to the manufacturers' instructions. Apply the finish to the moulding in the same order you intend to install the pieces. Then you won't have to spend as much time waiting for pieces to dry.
3. Set aside some finish to touch up any raw edge

• Install the Moulding

1. Locate and lightly mark the wall studs (see How to Find Studs in Finished Walls).
2. Measure the distance between two inside corners and cut a piece of moulding to fit between the corners. Predrill the moulding at every wall stud and nail in place. To avoid denting the moulding, use a nail set to finish driving the nails home. You may need someone to help hold long pieces while you drill and nail. In the event you have a span between two corners longer than the moulding, simply make a scarf joint as mentioned above to splice two pieces.
3. Continue installing pieces until all the moulding is up.
4. After all the moulding is up, touch up any raw edges with a light coat of finish. Use wood putty or a filler stick to hide nail holes. For crown moulding, it may be necessary to apply a bead of caulk where the moulding meets the ceiling to close any gaps.

• Installing Crown Moulding with Corner Blocks

1. Count the number of inside corners in the room to determine the number of inside corner blocks you will need. Do the same for the outside corners.
2. Predrill holes in the corner blocks and nail them to the corners of the room. Try to drill the holes so the moulding will cover them. If the room has any outside corners, predrill holes in the outside corner blocks and nail them to the outside corners of the room.
3. Measure the distance between the first two corner blocks. Cut a piece of moulding approximately 1/4" longer.
4. Butt one end of the moulding tight against one of the corner blocks. Lap the other end over the other corner block and trace the edge of the corner block onto the back of the moulding. Take the moulding down and cut it on the outside of the line to ensure a snug fit.
5. Locate and lightly mark the wall studs (see How to Find Studs in Finished Walls). Predrill the moulding at each wall stud and nail into place. To avoid denting the moulding, use a nail set to finish driving the nails home. You may need someone to help hold long pieces while you drill and nail. Continue this process until all the moulding is up. Use wood putty or a filler stick to cover any noticeable holes. If needed, apply a bead of caulk where the moulding meets the ceiling to close any gaps.