Adding plywood trim is an economical way to convert plain or outdated cabinets to shaker style:
Cut a sheet of 1/4-inch thick plywood into 2-1/4-inch wide strips along the length. A table saw is the best tool for this to ensure consistency.
Remove all the hardware from the cabinet doors. Sand the doors lightly to remove any dirt and gloss from the old finish.
Cut two of the plywood strips to the height of the door and apply wood glue to the backside of each. Align them so they are flush with the outer edge of the door as well as the top and bottom. Secure them to the door with 5/8-inch brads.
Mark two more strips of plywood and cut them to fit horizontally between the two vertical strips before you repeat the process to secure these strips.
If your flat doors have a beveled edge, fill the V shaped void between the plywood and the door with wood putty. Overfill the groove slightly in case the putty shrinks as it dries.
Fill the nail holes on the strips. Once the putty is dry, sand it down to create a flat edge all around the door.
Apply a coat of primer and two coats of finish paint to the doors before rehanging them.
Watch the video (https://www.todayshomeowner.com/video/how-to-convert-flat-cabinets-to-shaker-style/) for details.
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