Painting 101: Do I Really Need a Primer Coat?

Primer isn’t just another coat of paint. A primer serves as a barrier between the surface of the wall and the paint. It is usually made of different ingredients, as well as performing an entirely different function.  

If there are existing stains on the wall, or a dark paint that might show through the new topcoat paint you picked out, a primer coat will hide it. If you’re painting over a high-gloss or satin painted wall, the new topcoat will not have a rough surface to cling to and will likely require more work. With a primer base, you will sometimes need only one coat of the topcoat. It improves the paint adhesion to the wall, reduces bubbles, blisters, and peeling, and helps the paint last longer.

Also consider if you’ll be painting a high-traffic area, walls that take regular abuse from fingerprints, friction, or drastic changes in light, humidity, or temperature. A primer coat seals the surface and gives the topcoat something to stick to when oils and use would otherwise  be wearing it down.

Keep It Clean

To be sure the base coat can do its job most effectively, you need to apply it to clean walls. Dust or debris can add an unintended texture to the painted wall. For any painting project, it’s important to wipe everything down with a damp cloth, removing dust or oils that may be on the surface. If the walls have existing paint — and can handle it — give them a more thorough cleaning by wiping it first with water and diluted dish detergent.

A primer coat will even out some underlying textures to keep the top coat smoother, but the wall will still need to be prepared as thoroughly as possible. If grime or oils are painted over without first being cleaned or treated, they can allow mildew to grow between the paint and the wall, which is bad for the durability of the wall, as well as dangerous to people’s health. A base coat can protect against some of the dangers, but should not be relied on to prevent mildew.

Smoke Stains

If there is any smoke residue, it’s important to clean or treat it before painting. The residue can become a breeding ground for dangerous molds under the paint. An easy treatment for smoke grime is a solution of  one part bleach to one part water. Wipe the walls down with a damp rag using this mixture, and rinse the rag in a bucket of clean water in between. Once that’s done, wipe the wall with water again and let it dry completely before applying the primer coat.

Wallpaper Needs Primer

If you’re painting over wallpaper, be sure to use an oil-based primer coat. Water-based paints can reactivate the glue in the wallpaper, resulting in the paper warping and peeling under the new coat of paint. Make sure the wallpaper is clear of dirt or residue before painting a primer coat over it. If any seams have already begun to warp or peel, make sure to trim or scrape those sections off if they can’t be glued or spackled back in place. You can then take sandpaper to smooth out the paper’s edge before painting.

Keep in mind that the paint needs something secure to adhere to, and peeling or loose wallpaper won’t handle the weight of the paint. If the glue has weakened over large sections of the wallpapered surface, it’s probably best to remove the wallpaper and then wash and sand down the walls. The glue will leave a textured surface, so before painting, you will want to either sand it away, or intentionally texturize the wall to hide the straight lines and repeated patterns of the residual wallpaper glue.

Consider Your Options

There are some products out there that don't require a primer coat, and some that have the primer mixed in, so primer paint is not always necessary. It is a durable alternative, but for some homes, it may be an unnecessary extra step when a combination paint will do the trick.

So when do you need a primer coat?

• If the existing paint is a high gloss or a dark color, it might require more coats to completely hide it than an application of a base coat and two coats of paint could.
• If you’re painting on a concrete wall, you’ll want to use primer first.
• Fresh plaster walls that haven’t been painted before should have a primer coat.
• For stained wood railing, wainscoting, or paneling, apply primer before you paint.

Remember: Primer is most effective when you’re dealing with porous surfaces. Keep that in mind and use your best judgement to protect your home. Balance the advantages against the cost or the time requirements. Find the product that best suits your needs, and don’t take shortcuts.