How to Install Floor Trim at the Bottom of an Archway

Remove existing trim if necessary. If you're replacing the baseboard trim, take a utility knife and slide it along the caulk at the top of the baseboard. Peel back the baseboard with a putty knife, then remove the nails from the wall.

Measure the baseboard length along each side of the archway. If you already have archway trim installed, measure starting from the inside of the trim. Mark the measurements on your trim. Archway trim is the trim that outlines the archway.

Cut the trim to length. If you are joining the trim with another piece of trim at a 90 degree angle, cut the joining end at a 45 degree angle with a miter saw. This is typically not necessary if the trim is joining an existing archway trim, but some archways do not have an outlining trim. Use a standard table saw to make a straight cut.

Place one piece of trim along one side of the archway and another along the other side. If you have yet to install flooring, place a 1/2-inch spacer under the baseboard so that the flooring can be properly installed.

Nail the baseboard to the wall with a nail gun. Use four finish nails for each side, one at the top of both corners and the bottom of both corners. Always try to nail the trim into studs, although you may find it impossible if the length of the archway is less than 16 inches. Use a stud finder to locate studs.

Cut a 45 degree angle off the tip of a caulk tube. Place the tube inside a caulking gun. Line up the tip of the caulk tube with the gap between the trim and wall, at the top of the trim. Pull the trigger on the caulking gun and smoothly apply the caulk along the gap. Don’t allow the caulk to bead.

Apply a bit of caulk to the nail holes to cover them. Wet your finger and wipe away excess caulk. Ring out a sponge and brush it along the caulk line to finish the job.