How to Get a Straight Line When Painting Interior Walls

Clean the wall with soap, water and a rag. Only moisten the rag. You don't want to saturate the wall. Dirt and dust makes it harder for painter's tape to stick on the surface, and you'll end up with sloppier taped lines if you don't clean up the surface. Wait for the wall to dry before proceeding.

Measure your lines using a straightedge and tape measure. Lightly mark the lines on the wall with a pencil. For large wall surfaces, measure the lines in 2-foot increments, ensuring a straight line throughout each increment. Obtaining and using a large straightedge to mark the entire wall at once is just not practical.

Apply painter's tape to the edge of your line marks. Stick the tape on slowly, positioning it straight along the pencil mark. If your taped line accidentally wobbles, unstick and tear off the shakily taped area. Don't try to peel up the tape and then reuse it; once applied to a wall surface, the tape loses some of its adhesion, and it won't stick as well.

Prime an unpainted wall with general purpose latex primer. Primer helps seal fresh drywall for better results. Apply the primer near the taped lines using a synthetic-bristle paintbrush. Use a paint roller for vast wall areas where precision painting is not important. For previously painted walls, primer isn't necessary, as you can apply new paint over the old paint. However, primer helps you cover in fewer coats if you're going from a dark color to a light color, or vice versa. While priming is time-consuming, it saves time in the long run for a drastic color change.

Paint the wall with interior latex paint. Paintbrushes help you cover near the taped areas without overly saturating the wall, while a roller makes shorter work of large wall expanses.

Apply a second coat after two hours if there are bare patches on the wall.

Peel off the painter's tape after a full 24 hours. Latex paint dries to the touch in less than an hour. However, the paint won't fully cure for an entire day. Early paint removal leads to sloppier lines. When you remove the tape after a day, you'll find straight, clean lines underneath.

Erase any stray pencil marks from the wall using a vinyl eraser.