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Easy Crown Molding

TOH technical editor Mark Powers demonstrates how to install foam crown molding using nails and drywall finish.

Crown molding makes it to the top of most remodeling lists because it adds charm and value to a home, but depending on what kind of crown molding you use, it can be either a breeze to install or a hassle.

If you don’t want to take up an entire Saturday trying to get the corners just right, there’s a simple way to beat miter-saw frustration. Trimroc molding from Canamould Extrusions is a lightweight polystyrene foam coated in hard plaster. It cuts smoothly with a handsaw, and, as This Old House senior technical editor Mark Powers shows here, it goes up in a flash with joint compound. No coping, no tricky angles, and ragged joints disappear with a dab of mud.

Is foam crown molding any good?

Compared to wood, foam crown molding is not only affordable and easy to install, but it’s also pliable—making it easy to work with around the curvatures of your home.

Can you paint foam crown molding?

Yes. With foam crown molding, you can either spray paint or paint by hand. TOH’s Mark Powers demonstrates the latter. All you need is a couple coats of sealant and some latex paint. (Refer to Steps 10 and 11.)

Call Canamould Extrusions at 866-874-6762 for stock and custom orders and receive discount shipping to the United States.

Steps on How to Install Foam Crown Molding

1. Lay Out and Cut the Molding

Man Holds Strip Of Molding Above Door Photo by Kolin Smith

If you’re working with walls that are out of level and plumb, allow your eye, rather than a level, to guide the position of the molding. For best results, focus on getting the crown to look parallel with any neighboring trim. Install it starting at an inside corner and work toward any outside corners. Hold a strip of molding in place above a door or window casing. Adjust the molding until it looks even with the casing (ask a helper to stand back and look for you). Draw a pencil line to mark this positioning so that you can install the crown at this alignment.

2. Cut an Inside or Outside Corner

Man Cuts Molding In Miter Box Photo by Kolin Smith

To cut the molding at an angle for an inside or outside corner, place it in a miter box upside down and braced against the bottom and side of the box, as if it were angled against a ceiling and wall. Using a handsaw, cut the molding at a 45-degree angle. On an inside corner, the top part of the molding will be shorter; on an outside corner, the bottom part will be shorter.

3. Make a Tight Fit

Man Uses Sanding Block To Shave Crown Molding Photo by Kolin Smith

Using a rasp or sanding block, shave the back of the angled cut to create room for the two corners to come together tightly at the face.

Tip: Because straight butt joints are so easy to hide with this molding, you can cut the pieces shorter to make it easier to work.

4. Install the Molding

Man Uses Putty Knife To Spread Joint Compound Photo by Kolin Smith

The crown adheres to the wall with joint compound, but using too much will allow it to slide down the wall. As the compound sets, support long runs of molding with 8d nails.

Using a 6-inch putty knife, spread a ½-inch bead of joint compound the length of the molding along the top and bottom edges. Spread mud liberally on each cut end.

5. Match the Profiles First

Man Pushes Mitered Ends Of Crown Molding Together Photo by Kolin Smith

Push the two mitered ends together to create the inside corners, making sure their faces align in the corner. Match up the detail of the profile first, then use mud to fill any small gaps between the molding and the ceiling on either side.

6. Fit Together an Outside Corner

Man Pushes Foam Crown Molding Corners Together Photo by Kolin Smith

On an outside corner, press the mitered ends together until mud squeezes out of the joint. Backfill gaps using your finger or a putty knife.

7. Use Nails to Brace Long Runs

Man Uses Nails Under Crown Molding Photo by Kolin Smith

Along straight runs, push the straight-cut ends to create a butt joint. On long runs, place an 8d nail under the molding every few feet and at joints to hold it in place. Angle the nails up slightly to hide the holes, and sink them enough to keep them in place.

8. Smooth the Joints

Man Smooths Compound Over Seams Where Molding Meets Wall And Ceiling Photo by Kolin Smith

Cleanup will be easier if you clear away excess joint compound while it’s still wet.

Use your finger to smooth out the seams where the molding meets the wall and the ceiling. Use a wet sponge to help wipe away the compound and clean up the face of the molding. Don’t remove too much compound—if you do, the seams will “hollow” as it dries.

9. Fill to Excess

Man Uses Putty Knife To Push Compound Into Butt Joints Photo by Kolin Smith

Using a small putty knife, push more compound into and over butt joints. Pull the knife over each detail of the profile, leaving the compound a little proud of the joint. Once dry, the excess can be sanded smooth.

10. Prep to Paint

Man Sands Down Joint Compound Photo by Kolin Smith

Joint compound is easy to sand, and once you go over the seams where molding meets molding, the joints will almost disappear.

After the joint compound dries completely, sand down the excess using 150-grit sandpaper.

11. Mask and Paint

Man Paints Crown Molding Photo by Kolin Smith

Mask the walls along the edges of the molding with painter’s tape. Using an angled sash brush, prime and paint the molding to match the door and window casings in the room.


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