Make crown molding seams invisible

When crown molding seams that join two long lengths of crown molding are obvious, what is meant to embellish a room can be a distraction. Here is how to make crown molding seams invisible.

Billy Spencer of SRC in the Milwaukee area offers a way to hide and make crown molding seams invisible so that even the installer won’t be able to find it. He likes to work with 16-foot lengths. He uses a digital tape measure to determine that he will need 24 feet of crown molding to finish a kitchen wall − so he will need to join a 16-foot span with an 8-foot piece.

Here is Spencer’s 10-step process for cutting and binding the two pieces of crown molding together to make crown molding seams invisible so “no one will ever know. They’ll wonder how you ever got this long piece in here,” he says.

Work outsideSpencer advises crown molding installers to cut and glue the two pieces of molding together outdoors instead of trying to join them during installation. In the video, he creates the 24-foot length outdoors and then carries the finished piece inside to nail it to the wall.

Choose a cut

Installers typically cut one edge of each piece of molding at a 45-degree angle, which allows ample surface area for glue. Some, however, prefer a butt cut − a straight edge − because it cuts a smaller area and creates a shorter, less obvious joint between the two pieces.But Spencer makes a 22.5-degree scarf cut. It’s not a straight line, so there’s plenty of area to glue. But it’s less obvious than a 45-degree cut.Each of the two pieces gets the scarf cut on the end that will create the mid-wall seam, plus a 45-degree cut on the other end, where it will join another piece of molding at the intersection of two walls. Cut all ends with a miter saw, and then place both pieces of molding side-by-side, front side up, onto a sidewalk. Glue the pieces together. Spencer advises against gluing first, and then cutting.

Join the crown molding seams
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Slather on more glue than necessary. Spencer recommends applying cyanoacrylate glue, or CA, to the smaller piece and spraying an activator spray on the other piece for instant adhesion.
​Lift the newly joined extra-long piece of molding by tilting it toward you. Lay it back on the sidewalk so the back of the molding is facing up. Glue a small scrap piece of molding or wood to the back of the molding across the seam – that adds an extra layer of adhesion. Then, tilt the molding upward again and back down so the front is facing up.
Once the glue is dry, sand the molding at the seam to 4 to 6 inches on either side, using 80-grit sandpaper. Use steady, even pressure until the primer is sanded off. The seam will be nearly invisible. Then, switch to a 220-grit sandpaper to smooth the finish. A tip: Don’t sand off the detail of the molding.
Carefully shake the dust off of the molding and apply a light coat of spackle over the sanded area. Wipe the spackle with a wet rag to smooth it out. Let it dry in the sun, and lightly sand it again.

Put crown molding in place

Tilt the long, single piece of crown molding upward again, and, with a partner, lift it from the buttom and carry it into the house. Position the molding so you locate the seam away from any focal areas of the room.Snap the long piece into place and nail it to the wall. Fill the nail holes with spackle, and paint.
Although Spencer says this process for crown molding seams doesn’t work on vaulted ceilings, it’s fine for base molding. “We’ve never had any issues,” says Spencer.