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Install Decorative Moulding

Install Decorative Moulding

Installing moulding is a great way to refresh or redefine a room. You'll need a miter-cutting saw, basic carpentry tools and some basic woodworking skills.


Types of Moulding

There are several types of moulding materials to choose from. Installation is basically the same for each.

Architectural moulding is a low-maintenance material that you can saw, mill and work just like wood. It is even lighter than hardwood and handles more easily. It is a premium, polystyrene or polyurethane moulding with large profiles that mimic the look of built-up moulding. Architectural moulding doesn't warp, rot or split.

Decorative moulding gives your room a finished look and hides slight imperfections where corners meet. It is easier to install than many people believe, especially when you use corner blocks to eliminate miter cuts.

Medium density fiberboard (MDF) moulding cuts and works just like wood but with less movement due to changes in humidity and temperature. It's a lightweight engineered wood product that comes preprimed and ready to paint. Its workability and stability make MDF a good choice for any moulding application where a paint grade solution is desired.

Pre-finished moulding is a less expensive alternative to wood that still comes in several different wood grain patterns. Pre-finished moulding is made from polystyrene and comes ready to install, since the finish is applied at the factory, saving you the time and expense of finishing it yourself.

Unfinished solid wood moulding is the most common moulding used in homes.  It's assembled from pine or hardwood and milled in a multitude of profiles to correspond with almost any personal decorating style.

The most important tool when working with moulding is patience. Remember the old adage, measure twice and cut once. Never try to rush trim work.


Locating, Cutting and Fitting Decorative Moulding

miter saw
Decorative hardwood moulding can be installed in two ways. You can use the traditional installation method requiring miter, cope and scarf cuts or use the corner block installation method which allows you to install the moulding using only straight cuts.

General Tips
  • Start by cutting your decorative 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 to avoid splitting the moulding.
  • 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 outside corners, use a power miter saw and set it as indicated in in our crown moulding adjustment table below. 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.



Determining How Much You Need

Measure the room at the height where each moulding goes to determine the number and the length of the pieces you'll need. Jot these measurements down.

Architectural, prefinished, MDF and decorative moulding usually come in 8-ft 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.

Standard unfinished wood moulding usually comes in 8, 10 and 12-ft lengths. Looking at your list, calculate what lengths of moulding covers the area with the least waste. For example, if you have one wall that's 6-ft and another that's 5-ft, using a 12-ft piece of moulding yields both the 6-ft and 5-ft pieces, only leaving 1-ft of scrap moulding. However, if you used an 8-ft piece for the 6-ft wall and an 8-ft piece for the 5-ft wall, you'd be left with five feet of scrap.



Applying the Finish

Apply the finish to decorative hardwood 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.

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.

 

Set aside a small amount of the finish to touch up any raw edges.


Installing the Moulding


Step 1

Locate and lightly mark the wall studs.


Step 2
scarf joint

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.



Step 3

Continue installing pieces until all the moulding is up.


Step 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.

As an alternative, you can use adhesive to install most moulding. When using adhesive, you won't need a hammer, nail set or nails. Use only an adhesive recommended by the manufacturer.


Installing Moulding with Corner Blocks

inside corner block

To make installing moulding even easier, there are corner blocks and divider blocks. These blocks eliminate the need to cope, miter or splice when installing your moulding. Installing MDF moulding using corner blocks is very similar to installing decorative hardwood moulding using corner blocks.


Step 1

Determine how much moulding you need as above.


Step 2

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. Plan on using divider (intermediate) blocks in any wall with a measurement greater than 8-ft.


Step 3

Apply the finish as above.


Step 4

Predrill holes for nails to avoid splitting the moulding or corner blocks. Predrill holes in the inside corner blocks and nail them to the inside corners of the room. Try to drill the holes so the moulding covers 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.


Step 5

Measure the distance between the first two corner blocks. Cut a piece of moulding approximately 1/4" longer than the measurement.


Step 6

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.


Step 7

Locate and lightly mark the wall studs. Touch up the raw edges with a light coat of finish and fit it between the corner blocks. Predrill the moulding at every other 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.


Step 8

In the event you have a span between two corner blocks longer than the moulding, simply center an intermediate block between the two corner blocks. Install the moulding as you would between corner blocks.


Step 9

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.



Building Up Moulding

Built-up moulding is usually associated with intricate crown mouldings on vaulted ceilings or the ornate mantels of colonial mansions. Although those patterns may overpower the average home today, you can use the same techniques to design your own personalized moulding. Gather several sample profiles. Experiment with them until you find a profile you like.

Once you decide on the profile for your built-up moulding, determine which piece should go up first. Select the most rigid piece or a piece that butts to a rigid surface like the floor or ceiling. Starting with the most rigid piece ensures straight lines and eliminates the flex that smaller mouldings can have. Next determine the order for installing the rest of the pieces.

Install the first piece as you would a single profile. Install each subsequent profile in its entirety before going on to the next.



Cutting Crown Moulding

Here are the compound miter saw adjustments for cutting crown moulding.

Wall Intersection Angle
Crown Moulding with
52° and 38° Edges
Crown Moulding with
45° and 45° Edges
Miter Adjustment
Bevel Adjustment
Miter Adjustment
Bevel Adjustment
85°
33.90
35.52
37.66
31.42
86°
33.43
35.19
37.17
31.14
87°
32.97
34.86
36.69
30.86
88°
32.52
34.53
36.21
30.57
89°
32.07
34.20
35.74
30.29
90°
31.62
33.86
35.26
30.00
91°
31.17
33.53
34.79
29.71
92°
30.73
33.19
34.33
29.42
93°
30.30
32.85
33.86
29.13
94°
29.86
32.51
33.40
28.83
95°
29.43
32.17
32.94
28.54

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