How to Trim Door Jambs

New trim can give your doors an updated look.

Door jambs usually have some kind of trim around them. If not, or if the old look needs an update, a do-it-yourself can install trim. Adding trim isn't easy, but with the right tools and a little preparation, anyone can complete this task. Trim around door jambs adds style and a complete look to the home, and can be installed inexpensively unless you choose a custom design.

Things You'll Need

• Pencil
• Tape measure
• Wood saw
• Finish nails
• Hammer
• Acrylic caulk
• Caulk gun
• Paint
• Paintbrush
• Utility knife
• Light-duty pry bar
• Triangle square
• Sawhorse

Instructions

Preparing a Door Jamb with Existing Trim

1. Slice the caulk with a utility knife along the seams of the door jamb trim.

2. Tap the pry bar lightly with the hammer between the door jamb trim and wall.

3. Pull the pry bar lightly toward you along the length of the door jamb trim until it is completely removed from the wall. Make sure not to pull too hard, as this can damage the wall.

4. Remove any remaining caulk, nails, and paint residue along the wall and door jamb, using the utility knife.

5. Measure the height and width of the door jamb, using a tape measure. Cut the trim to fit these measurements with a wood saw.

Cutting Side Trim at a 45-Degree Angle

1. Mark the inside edges of the side trim with a pencil precisely at the corner of the door jamb opening.

2. Place both pieces of side trim on a sawhorse and make a mark with pencil 1/4 inch above the previous mark. This will be the low side of the 45-degree angle cut.

3. Place the triangle square on the trim so that the 45-degree angle of the triangle square is flush with your low-side cut and draw a line from one side to the other.

4. Cut the trim along the 45-degree-angle line, using a wood saw.

Placing Cut Side Trim on Door

1. Measure 1/4 inch from the sides of the door jamb opening.

2. Place the side trim at the 1/4-inch mark along the sides of the door jamb opening.

3. Drive the first finish nail into the the tops of the side trim with the hammer, the second nail into the bottoms, and place five to six nails along the trim. Drive the nails flush with the trim surface.

Cutting Top Trim at a 45-Degree Angle

1. Dry-fit the top trim along the top of the door opening 1/4 inch away from the door jamb's edge.

2. Mark the top trim on its bottom edge directly at the points where its meets both of the low sides of the 45-degree angle cuts on the side trim. Also mark the top trim on its top edge directly at the points where it meets the high side of the 45-degree angle cuts on the side trim.

3. Make cuts on both ends of door jamb top trim between the marked point. Again, make sure the high side of the trim is out and the low side is in.

4. Place the cut door jamb top trim flush against the previously-placed side trim so that all 45-degree angles meet. This will look similar to a picture frame.

5. Drive nails on both ends, and then finish driving four or five nails in the middle.

Caulking and Painting the Trim

1. Apply caulk to every seam along the door jamb, wall, floor, and at the 45-degree-angle cuts, using a caulk gun

2. Smooth the caulk with a finger, wiping away any excess. Let the caulk dry for approximately 30 minutes.

3. Paint the door jamb trim, using a paintbrush. Let the paint dry one to two hours, then add a second coat.

Tips & Warnings

• A finish nail gun makes makes for a smoother trim surface, but isn't necessary.

• Add 3 to 6 inches to all measurements to allow for precise cut and fit.

• Do not nail door jamb top trim until it will sit flush with pieces of side trim.

References

• Home Addition Plus: Installing Interior Door Trim