When to prime
- New drywall or bare surfaces: porous surfaces absorb paint. PaintCare’s Buy Right guide says unprimed surfaces absorb more paint and need more coats.
- Big color changes: primer reduces the number of top coats; PaintCare suggests a gray primer when changing to red.
- Stains and smoke or water marks: use a stain-blocking primer.
- Glossy surfaces: use a bonding primer and scuff-sand first.
When you can skip it
Repainting a similar color over clean, sound paint. Some paints are sold as paint-and-primer in one; check the label and the coverage it states.
Cost example
For a 12 × 12 room (334 sq ft of wall), one coat of primer at 250 sq ft per gallon is 1.34 gallons. At typical prices that is 2 gallons, $60. Use the primer calculator for your area and surface.
Estimates only. Check your paint can’s label for coverage. Prices are typical 2026 US figures; use your store’s.