How to Make a Scarf Joint

For the best appearance, moldings should run in one continuous strip from one corner of the room to the next. But when the room is longer than your molding, a joint becomes unavoidable. Your task, though, is to make that seam as invisible as possible. The solution is a scarf joint. Made with 45-degree cuts, this seam won't take any attention away from the beautiful room it sits in. Learn how to make one for your own home makeover using our helpful tips below.

Disguising the Joint

Below, we provide the steps you'll follow to make am undetectable scarf joint—but there are several other things you can do to disguise the joint. If you're joining wood that will get a clear finish, join pieces that have the same subdued grain pattern. Joining a wildly grained strip with one that has straight grain will make the difference immediately apparent.

If possible, locate the joint where a bed, bookcase, or other large piece of furniture will hide it. That way, the only time you'll see the seam is on moving day. Behind a door is another good spot, but be careful of positioning a joint too close to a corner. A seam closer than 16 inches from a corner may look as if you're fixing a mistake — not making a planned extension.

Painted scarf joints are easy to conceal, but they still require careful workmanship and sanding. Paint is merely a finishing coat, not a cure for a poor fit.

If you apply stain and a clear finish before cutting the scarf, you won't have to sand the joint smooth. Although this will save the effort of applying the finish after installation, it means that you'll need to spend extra time to fit the joint as closely as possible. Touch up the joint's ends with a stain pen to eliminate the appearance of raw wood.

What You Need

• Stud finder
• Pencil
• Tape
• Miter saw
• Nails
• Hammer
• Drill
• Sandpaper
• Glue
• Touch-up paint

Step 1: Find a Location

Select the location for the scarf joint, positioning it over a stud, if possible. Mark the stud's edges and centerline onto a piece of tape applied to the wall.

Step 2: Mark the Cut Line

Fit the end of one molding piece into a corner, then mark the seam cutting line. In this example, the corner at right is fitted first. To help your cutting, mark diagonally across your molding piece.

Step 3: Make the First Cut

Make the first half of the scarf joint with a 45-degree miter cut that opens away from the wall. Nail this piece to the wall at the other stud locations along the wall.

Step 4: Make a Second Cut

Fit the end of the second molding strip into its corner, and mark the location of its scarf joint. Notice that the miter runs in the opposite direction as the cut in the first piece you installed. Make several cuts in order to sneak up to a perfect fit.

Step 5: Pilot Holes

Drill pilot holes for the nails that will secure the seam and hold the molding to the wall. Don't neglect this step, since the glue makes the joint slippery, and the pieces can shift out of position as you're driving the fasteners. Slightly angle the pilot holes so the joint doesn't slide apart when you drive the nails.

Step 6: Drive Nails and Sand

Apply glue to both ends of the joint. Get both nails started through the pilots before you drive either one of them completely. Countersink the nails as little as possible. Sand the joint smooth and touch up the paint.

Smart Sanding Tips

Flat Edge

Load abrasive paper into a hard rubber sanding block to level the flat surfaces of scarf-joined moldings. Don't concentrate sanding pressure right at the joint line—feather out the sanding several inches to each side of the seam line. Remove dust with a tack cloth, then apply primer to the raw wood.

Curved Edge

Smooth curved surfaces with sandpaper wrapped around a rod or cylinder that matches the molding. Some good cylinders include round pencils, dowel rods, and PVC plumbing pipe. Pressure-sensitive abrasive (PSA) sticks to the cylinder, making your work easy. Spraying adhesive on ordinary sandpaper is a good alternative to a PSA.

Large-Scale Scarf Joints

On some large pieces of trimwork, such as crown molding, you can join lengths prior to installation. Doing this significantly reduces the amount of work you need to perform while standing on a ladder. As a result, you get better joints with less work.

Accurate cutting of the opposing miters for the joint is still an absolute necessity. Follow the recommended setting time, and before proceeding to the installation, be sure that the assembled joint has developed strength in the glue joint.

For the wood gusset, cut the scarf joint, apply glue to the cut ends, and press them together firmly. Align the assembly against a straightedge and apply strips of masking tape to keep the joint shut. Glue and screw a plywood gusset over the seam. As the size of the molding increases, choose thicker plywood, but make certain it doesn't interfere with the installation clearances. Steel mending plates are a good alternative to plywood, lending excellent strength with minimum bulk. Choose coarse-threaded screws for maximum holding power in softwoods. During installation, don't attempt to drive or shoot nails through the metal plates.