Many contractors substitute ceiling paint for drywall primer when a shortage of time won’t allow a trip to the hardware store. You may do this, but you have to use more paint to get the job done. Ceiling paint is a finisher, not a sealer; consequently, rough drywall soaks it up like a sponge.Click to see full answer. Regarding this, can you use ceiling paint as a primer?People generally use their ceiling paint leftover as a primer to paint the walls: a ceiling paint is normally white and has the same qualities as a paint sealant; it can be easily used as a primer. Ceiling paint is usually costlier than primer.Likewise, what happens if you don’t use primer before painting? Proper Paint Adhesion Because it has a glue-like base, drywall primer helps the paint adhere properly. If you skip priming, you risk peeling paint, especially in humid conditions. You might blame this on the quality of paint you used, but the truth is that failure to use primer caused the problem. One may also ask, do I need to prime my ceiling before painting? Ceiling paint can crack, peel or appear chalky if you don’t prepare the surface properly. Not every ceiling, however, needs to be primed when painting ceilings. You can tell if your ceiling requires primer by looking at its existing finish, condition or material.What is the difference between a primer and an undercoat?While the primer paint is used right before painting a new surface, the undercoat paint is used before painting a surface that has been painted in the past. In other words, an undercoat can be a primer but a primer is never an undercoat. Primers work best on flat wall surfaces and low-gloss ones.