Do you need primer? A plain guide to when it matters

When primer is worth the extra step

Paint makers agree on the short list. Benjamin Moore recommends primer on bare surfaces that have never been painted, surfaces sanded down to the bare material, places with rust or stains, dramatic color changes, and hard-to-coat surfaces like plastic, laminate, glass and anything high-gloss or non-porous. Dunn-Edwards adds the one most homeowners meet first: new or repaired drywall.

Why new and patched drywall needs it

Raw drywall is porous, and it isn't one material. The paper face, the seams and the joint compound over them each soak up paint at a different rate. Without primer, those areas dry to different sheens and show through the paint as dull, blotchy patches.

Patches work the same way. Joint compound and spackle need sealing for even coverage, which is why a wall that looked perfect before painting can show every repair afterward. On every interior painting job we repair small holes, and a repair isn't finished until it's primed.

When you can skip it

If you're working with a previously painted surface in good condition, Benjamin Moore says you most likely don't need to prime. A clean wall that's painted a similar color is the classic case: the old paint already gives the new coat something to grip.

Dunn-Edwards draws the line in a useful place. A good paint can count as self-priming on interior drywall if all you need is adhesion and hide, but only on a properly prepared surface, one that's clean, free of contaminants like ink, pencil, food and dirt, and free of stains.

What primer actually does

Primer isn't thin paint. It's a different coating, built to do jobs paint can't: seal a porous surface, grip a slick one and block stains. Dunn-Edwards lists the benefits as sealing in stains from ink, water or wood tannins, giving a smoother and more even finish, and making a stronger bond between the topcoat and whatever's underneath.

That bond is the part you can't see and will care about later. Paint that never gripped properly is the paint that peels, and primer is where that grip gets made.

Dunn-Edwards also lists two situations that surprise people. In high-traffic areas, primer strengthens the surface so the paint stays intact longer. In moisture-prone rooms, sealing the surface helps paint resist peeling and bubbling. Neither one replaces fixing a damp wall first, but both are worth knowing before you decide to skip the step.

Paint and primer in one

"Paint and primer in one" is real, and it works on the right walls, with limits. Benjamin Moore says its paint-and-primer products are self-priming on most properly prepared surfaces, yet it still recommends two coats for full color development and the best performance. Dunn-Edwards is blunter: "self-priming" only means the paint will adhere to a surface that's been properly prepared, and it generally doesn't do the job on stained walls.

Treat it as a convenience for sound, clean walls, not a cure for stains or big color changes. On those, a dedicated primer does the work. Benjamin Moore also notes that some custom colors need a deep base primer tinted to a special formula to come out right, and suggests asking your retailer about special-purpose primers if the surface is water stained, smoke damaged, grease stained or very slick.

Choosing a primer for the job

• New drywall: a drywall primer-sealer, made to even out the difference between the paper and the joint compound.
• Stains and smoke: a stain-blocking primer. Some stains bleed through most primers and paints no matter how many coats go on, and the same goes for smoke odors.
• Bare wood: a wood primer. Drywall primer isn't made for the tannins in woods like pine, redwood and cedar. Knotty pine walls are the classic case, covered in how to paint shiplap.
• Old oil-based paint or a slick surface: a bonding primer.

Primers also come in two families. Acrylic primers are easier to apply and clean up with water, and they suit almost any surface except where rust is present. Alkyd (oil-based) primers block stains best, including tannin-rich wood, smoke and water stains.

Finding out what's already on the wall

The old paint decides which primer you need, and it's easy to identify. Dip a cotton ball in rubbing alcohol and rub it on a hidden spot. If paint comes off on the cotton, it's latex or acrylic. If it doesn't, it's oil-based. Our post on latex versus oil-based paint explains what to do in each case.

Do the test even in a house where you're sure. Older homes can have layers of oil-based paint on the trim, and it's an easy thing to get wrong by assuming.

Glossy trim and old oil-based paint

Slick surfaces are the other place primer isn't optional. Dunn-Edwards describes old oil-based enamels as paint that never quite stops hardening: the surface keeps getting harder and slicker with time, and water-based paint doesn't wet it well, so repainting it is a bit like painting glass.

The fix is prep, then primer. Clean off cooking grease, fingerprints and any other residue. Then dull the gloss by sanding. Dunn-Edwards says a light scuff isn't enough, and the surface needs to end up essentially flat. Wipe off the dust, prime with a bonding primer, and only then put the topcoat on. Skip a step and the new paint may not hold. It's the same prep that goes into painting interior doors. On cabinets, our post on painting cabinets without sanding covers when a bonding primer can stand in for sanding. Our guide to the best primer for cabinets matches primer types to cabinet surfaces.

Priming in the right order

Dunn-Edwards lays out the sequence for drywall, and it's the one we follow:

1. Clean the walls and let them dry completely.
2. Fill dents and nail holes, then sand lightly so the repairs are smooth.
3. Wipe or vacuum the dust off. Dust gets in the way of adhesion.
4. Roll the primer on wide areas and brush the corners and edges. One even coat is usually enough for standard walls.
5. Let it dry fully. Check the label for drying time, and keep the room ventilated.

That's clean, sand, repair, prime, then paint, with floors and furniture covered before any of it starts. If you're doing it yourself, our guide to prepping walls for painting goes into more detail, and how many coats of paint explains how primer changes the count.