Painting Up To A Popcorn Ceiling

Q. I am going to paint some walls in my house and we have popcorn
ceilings (which I hate). What is the best way to not get pain on the
ceiling around the edges? I can't tape..can I?

A. Taping the a popcorn ceiling is difficult, the paint will usually get behind the tape, because you cannot get a tight seal.

Use a 12" wide, plastic drywall knife held in the angle of the ceiling where it meets the wall, hold it at about a 30 degree angle and using a paint brush, paint the wall. The drywall knife will keep the paint from touching the ceiling.

Make sure you wipe the edge of the knife often, as paint will build up there and will run to the ceiling side of the knife.

Link