Clean Moldings Before Applying Painter’s TapeEven the stickiest masking tape won’t stay put if you apply it to a dusty, dirty surface. You’ll save yourself a lot of time and frustration if you start every masking job by cleaning the moldings or the wall to which you’re applying the tape. Usually a thorough dusting with a damp rag is all that’s required. But if the surface is greasy, you’ll have to wash it with a detergent solution. TSP-PF (phosphate free), available at home centers and paint stores, is the go-to detergent for most painters. Wait for the surface to dry completely before masking.