Installing quarter-round molding is an inexpensive way to make a simple piece of baseboard look better or provide a neat finish to a flooring job. It can also be used by itself to create a clean look in a room. Quarter-round comes in different sizes. The most common size is 3/4-inch. When adding a piece of quarter-round to the top of a piece of 1-inch trim, use 3/4-inch quarter-round. This would match the top of the board perfectly. If you are placing quarter-round in front of the baseboard use any size you prefer or that will fill any gaps between the end of your new flooring and the wall.
Make your first cut at a 45-degree angle using your miter box and saw, then make your measurement for the total length. If you are adding quarter-round molding to a four-cornered room, then all your cuts will be at a 45-degree angle with the angles running towards the center of the piece of molding.
Make butt joints where the baseboard meets the door trim. Every room has to have at least one door opening, so whenever you come to a door frame you can run the molding right up to the frame without cutting an extra 45-degree angle. Just make sure the butt joint is at a perfect 90 degrees. Don' trust the lumberyard; always cut the end of a piece of quarter-round before you place it.
Wrap the molding around any abutments in the wall using a 45-degree miter joint. In this case, you will cut the angles in the exact opposite way that you did in Step 2. That means the angle begins at the curve in the wood and runs into the center of the piece of molding at a 45-degree angle.
Splice together any pieces of molding with two 45-degree cuts that run in different directions. These cuts should fit together tightly and most likely will not be noticed if they are done right.
Nail the molding to the floor at an angle using #6 or #8 bright-finish nails and set each nail with a small nail set.
Fill each nail hole with wood putty. If necessary, you can fill the wood joints with putty, but a clean and careful cutting job should eliminate the need for this step.