Frequently Asked Question Should I prime before painting? Is it always necessary to use a primer before painting? Glidden recommends that a primer always be applied prior to the topcoat for both interior and exterior projects. There are several key reasons to prime: INTERIOR Use on any new or bare surface to seal the surface Prevent smoke or water stains from consistently bleeding through to the surface Prevent grease and mildew stains from bleeding through Making a major color change Painting over a glossy surface Don't know when last painted; so topcoat will not be absorbed into the surface Ensures great adhesion of the topcoat which will promote: Greater color retention Greater wash and scrub resistance Makes for a more uniform attractive appearance of the topcoat Ensures better holdout if topcoat has a sheen EXTERIOR Use on any new or bare surface to seal the surface Ensures great adhesion of the topcoat Helps prevent blistering, cracking and peeling of topcoat Offers better color retention and fade resistance Helps control growth of new mildew Needed to cover stains or major changes to ensure complete coverage of topcoat Needed to cover old chalky or weathered surfaces In addition to the above reasons, a primer can also be tinted with a topcoat colorant to help promote coverage. This becomes necessary when you're working with a dark or accent color. It is advised in this situation that you can only add two ounces of colorant per gallon of primer.