Do I Really Need a Primer? When You Can (and Can’t) Skip It

Professionals often estimate that 80–90% of a great paint job is prep work—cleaning, sanding, patching, priming, and masking—while actual painting is the easy final 10%.

Primer isn’t about “more coats.” It’s a targeted step that solves three problems paint can’t always handle on its own: adhesion to tough surfaces, sealing porous substrates so topcoat lays down evenly, and blocking stains so they don’t bleed back through. Sometimes you can skip it. Often, you shouldn’t. Here’s how to decide with confidence.

What Primer Actually Does

1. Adhesion: Creates a sticky bridge between the surface and the paint, reducing peeling and chipping.
2. Sealing: Levels out porosity so your topcoat doesn’t flash or require extra gallons.
3. Stain blocking: Locks in water marks, smoke, ink, knots, and wood tannins so they don’t telegraph.

When You Can Skip Primer

• Repainting a sound surface with the same type of paint: Clean, dull, dry walls or trim with no stains or glossy spots can often go straight to topcoat.
• Minor touch-ups: Small scuffs or nail holes that you’ve patched and feather-sanded may blend with careful topcoating.
• Self-priming paints on previously painted walls: Some high-quality wall paints are formulated to build film and hide without a separate primer—assuming the substrate is clean and uniform. Be EXTREMELY wary of these claims. In our experience, the time or money you save now will come back to get you.
• Tiny sheen shift: Moving from eggshell to satin (or vice versa) on intact(and clean) paint, after a light scuff-sand, frequently needs no dedicated primer.

When You Should Use a Primer

• New drywall or fresh joint compound: The paper and mud absorb at different rates, causing flashing. Use a drywall primer for clean, new gypsum with no stains present. We recommend C2 Wallboard Primer
• Any stains: Water rings, nicotine, marker/ink, knots, or wood tannins call for a stain-blocking formula. Read our full guide on interior stain blocking primers. For most interiors, an acrylic stain blocker like C2 One All-Purpose Acrylic Primer is a strong first choice.
• Glossy, slick, or previously oil-painted surfaces: Doors, trim, cabinets, and old alkyd finishes need a bonding primer to prevent peeling. Most pros prefer a high build/sandable primer like C2 SAP.
• Bare wood: Primer seals end grain, evens porosity, and reduces grain raise. Knots or extractive-rich woods may need spot priming with a severe-stain sealer before an overall acrylic prime.
• Metal (interior or exterior): Use the appropriate metal/DTM primer system to inhibit corrosion and promote adhesion. There are exceptions. Some paints use a DTM resin and do not require primer. These are normally premium products and come at a premium price. We recommend C2 Exterior(only the Satin sheen uses the DTM resin).
• Masonry, brick, or concrete: Alkali-resistant primers manage high pH and moisture vapor so paint doesn’t blister or effloresce.
• Big color changes: Switching from dark to light (or vice versa) benefits from a high-hiding prime coat tinted toward the finish color.
• Patchwork surfaces: Spackle, joint compound, and spot repairs show through topcoat without a unifying prime.

Interior Go-To: A Practical Default

For general interior work where stains or mixed surfaces are involved, we often start with C2 One All-Purpose Acrylic Primer. It balances adhesion, sealing, and common stain resistance with low odor and easy recoating. Note that C2 Wallboard Primer is not stain-blocking—reserve it for clean, new drywall without discoloration.

Exterior Primer: Different Demands

Outside, moisture and UV are the real enemies. A dedicated exterior primer adds breathability (letting vapor out) while resisting liquid water and sun exposure. For siding, trim, and weathered wood, see C2 Exterior Acrylic Primer for a breathable, stain-resistant base that supports long-term topcoat performance.

Quick Decision Guide

• New drywall, no stains: Drywall primer (for example, C2 Wallboard Primer).
• Interior with stains or mixed substrates: Acrylic stain-blocking primer (for example, C2 One).
• Exterior wood or weathered surfaces: Exterior-grade primer (for example, C2 Exterior Acrylic Primer).
• Severe localized stains (marker, knots, heavy nicotine): Spot-prime with a shellac or specialty blocker, then overall prime with acrylic.

Prep and Application Tips

• Clean first: Remove dust, grease, smoke residue, and surfactants. Stains left on the surface will telegraph.
• De-gloss shiny areas: Lightly sand or use a liquid deglosser so primer can bite in.
• Mind moisture: Wet substrates trap vapor. Allow full dry and use breathable systems, especially outdoors.
• Build smart film thickness: Don’t lay primer heavy in one coat; even, well-cured coats seal better and reduce future peeling.
• Test suspicious areas: Do a small adhesion test when painting over unknown or aged coatings.

Bottom Line

Skip primer only when the surface is clean, sound, and uniform—no stains, no gloss, no bare spots. Use primer whenever you need better adhesion, sealed porosity, or true stain blocking. Choosing the right primer upfront reduces coats, improves finish quality, and helps your paint job last.