A bit harder to do, but the results are a hundred times better. And the actors can rehearse with the walls up, too. Uh, obviously, paint the trim before it is mounted to the set. Texturing Don't leave any wall a single, plain, one color. Using a tint of paint lighter and one darker, give the wall some sort of texture.
Spattering is the usual application manner.
Now raise the brush shoulder height and bring brush and arm sharply down to about 45 degrees above your waist. You should be rewarded with the pitter-pat of thousands of little spatters. You will quickly figure out how to aim higher and lower. And to spatter every which way - as you do not want to have any kind of pattern to the spatters. Other Application methods Check with any Theatrical text and you will find that most anything will apply paint.