Do you have to prime before painting? Avoid these common mistakes

Paint needs the right kind of surface to adhere to and spread evenly. When the conditions aren't right, problems can show up in the finish or how well the paint holds up over time. That’s where primer often comes in. But do you have to prime before painting every time?

In this article, we’ll explain when primer is needed before painting, when it can be skipped, and how to prime a wall correctly for optimal results.

When is primer needed before painting?

A primer before paint isn’t always required, but there are times when it becomes essential. Skipping it in those cases can lead to peeling, patchy color, or poor durability.

Painting new drywall or fresh plaster

New drywall and fresh plaster have a sponge-like quality due to their mineral-based composition. When you apply paint directly to them, the surface absorbs the liquid components of the paint faster than it should. This leaves behind uneven pigment and binders, causing patchiness, dull spots, and an inconsistent texture known as flashing.

In contrast, primer contains high levels of binder and fewer pigments. It solves this drywall issue by soaking into the surface first and sealing up those tiny pores. It creates an even base so that the paint won’t absorb at different rates across the wall. As a result, when you paint over it, it dries evenly and adheres better across the entire surface.

Bare wood or unpainted surfaces

Bare wood is filled with tiny tubes or vessels called capillaries. These absorb liquids, which means paint will disappear into the wood grain instead of sitting neatly on top. Bare wood also contains natural oils and tannins that can rise through paint layers and create brownish stains or yellowing over time, especially if you’re using light-colored paint.

A good wood primer blocks this from happening in two ways. First, it fills in the wood’s natural pores and prevents blotchy absorption. It also creates a physical barrier that traps oils and tannins, preventing them from reaching the surface. This keeps the final paint layer clean, even, and better protected from peeling or discoloration.

Making a dramatic color change

When switching from a dark wall color to a much lighter one or vice versa, you’ll run into problems with the old color bleeding through. Lighter paints typically have less pigment and are not designed to cover deep colors in just one or two coats. This leads to uneven coverage and frustration.

Primer works by creating a neutral layer that blocks the old color and provides the new paint with a more balanced surface to adhere to. Tinted primers are even better in this case. They’re customized to match the new paint color more closely. This way, the new paint doesn’t have to work as hard to hide what’s underneath. For example, if you’re painting a red wall white, using a gray-tinted primer can reduce the amount of red that shows through and make it easier for the white paint to cover in fewer coats.

Covering stains, odors, or water damage

When dealing with stubborn wall stains caused by smoke damage, grease, crayon marks, mildew, and water spots, paint alone is insufficient to conceal or seal them. Primer contains heavy-duty resins that sit on the surface and lock in contaminants, preventing them from bleeding through the new paint.

Glossy, slick, or hard-to-paint surfaces

Surfaces that are shiny or very smooth, such as glossy painted walls, laminate, metal, vinyl, plastic, or tiles, don’t give paint much to grip onto. As such, paint sits on top instead of bonding, which makes it easy to peel, scratch, or flake off with time or cleaning. 

Bonding primers contain special adhesion-promoting resins that chemically bond to slick materials, creating a surface to which the new paint can adhere. Think of it like applying a thin layer of glue that holds everything together. The primer grips the smooth surface underneath while also bonding tightly with the new paint layer on top.

Painting over oil-based paint

Most modern paints won’t adhere to oil-based surfaces. If you apply latex paint directly over old oil-based paint without a primer, it may peel or chip within weeks, no matter how clean the surface is. This happens because oil-based paint forms a hard, slick film that resists water and anything that doesn’t bond chemically. 

Since latex paint relies on surface grip and flexibility, it cannot penetrate or adhere to the glossy, oil-based layer. A bonding primer creates a bridge between the two. It contains adhesion agents that bond to the oil-based surface and form a layer, allowing latex paint to adhere correctly.

Do you have to prime before you paint every surface?

Not always. Primer is designed to solve specific problems, and when those problems don’t exist, you can skip priming.

Situations that don’t require priming include:

• Repainting a clean, smooth wall with the same type and color of paint.
• Bare drywall with PVA (polyvinyl acetate) primer already applied during installation.
• High-quality self-priming paint used for surfaces that don’t have adhesion or coverage issues.
• Minor drywall repairs, where spot priming just the patched area is enough.

A common misconception is that primer is always required to get a professional-looking finish. In reality, if you're working on a well-prepped, previously painted surface, applying primer won’t improve the result.

How to prime a wall for painting

The goal of priming walls to paint is to create a smooth, clean base. Here's how to get started, step by step:

• Clean and dry the surface: Use a damp cloth or sponge to wipe the surface down. Dust, dirt, grease, or even small spider webs can prevent primer from sticking properly. For oily areas, use a mild soap or degreaser. After cleaning, let the wall dry completely.
• Choose the right primer for the job: Not all primers do the same thing. If you're painting new drywall, use a drywall primer. For bare wood, a wood primer blocks out stains and prevents uneven absorption of the wood's natural tannins. Are you covering tough stains like water spots, smoke damage, or crayon marks? Go for a stain-blocking primer. Need to paint over a slick or glossy surface, such as metal, tile, or laminate? You’ll need a bonding primer. If you're unsure which one to use, ask at the paint store and describe the surface you're painting.
• Apply the primer evenly with a roller or brush: Stir the primer well, just like you would with paint. Then, use a roller to cover larger areas, and a brush for corners, trim, and along the ceiling line. Apply it in smooth, even strokes, working in small sections. You don’t need to apply it too thick, but ensure the wall is covered evenly without drips or streaks.
• Let it dry fully: Drying times vary based on the type of primer and room conditions. Most latex primers dry within the hour, while oil-based primers require between 1 and 4 hours. Check the label on the can for exact timing and ensure that the primer completely dries before painting over it.

Do you need to prime painted walls?

Priming your painted walls depends on the condition of the wall and what type of paint is already on it. If you're repainting a wall that was previously painted with latex paint and it's still in good shape, you usually don’t need a primer. However, if the wall has a glossy finish or was painted with oil-based paint, you will need a bonding primer to create a surface that the new paint can adhere to.

Unsure what type of paint is on the wall, perform a quick test? Rub a small area with a cotton ball soaked in rubbing alcohol. If some paint comes off, it's latex. If nothing comes off, it's likely oil-based.

Final thoughts: Is paint primer necessary?

Paint primer isn’t always required. However, when it is necessary, skipping it can lead to problems, such as using more coats of paint than expected, an uneven finish, or the paint not adhering well.

If you're unsure whether a surface needs primer, perform the rubbing alcohol test. It’s safer to err on the side of caution and apply primer if unsure. It acts as a foundation that helps your paint job look better and last longer.