A. Applying a coat of drywall primer is always a good idea, for several reasons.

• Primer is generally less expensive than wall paint, so you will save money.
• A single coat of paint on unprimed drywall would look bad. Depending on the paint, you may be able to get away with a single coat over a well primed wall.
• Using a sealing primer on exterior walls will provide a vapor barrier to keep moist interior air out of the insulation in the wall. See article.
• Since the joint compound that is used to finish the drywall joints is water soluble, you may disturb the smoothness of the finish when rolling out the paint. Primer tends to dry more quickly and reduces the chance that this will happen.