There are a few cases in which you will always need to prime before you paint:
- If the surface is porous
Always prime walls before painting if the surface is porous. The surface is porous when it absorbs water, moisture, oil, odors or stains. For example, brand new drywall is a very porous material. Both the paper that covers it and drywall mud are made up of water or moisture when they are not sealed first with primer. If you don’t prime it first, this material will absorb your paint right into it. Other examples of porous surfaces include untreated or unstained wood. For example if you’re planning on painting a set of shelves, you will definitely want to prime first.
- If the surface is glossy
Glossy surfaces are difficult for paint to stick to. If the wall is covered in a high gloss paint or enamel you could paint coat after coat and never have it adhere properly.
While these surfaces will definitely need primer, we also recommend a light sanding beforehand as well. This step will ensure your walls’ surface has enough texture so both the primer and paint can bite onto the surface and adhere perfectly.
- If the surface is stained
If your walls have stains caused by old water damage, smoke stains from cooking or candles, or kids simply using the walls as a canvas for their “artwork”, you’ll want to prime first. Because primer acts like a sealant/blocker, it will seal these stains in so they won’t leak back or show through the paint.
Prior to priming over stains, it is critical in some cases that you fix any problems that led to the staining in the first place. For example, if you have old water stains, make sure that the leak is fully repaired before you paint. It will cause more problems later if you don’t.
- If the surface has an odor
We have all been around at some point a home with a less than pleasant odor. All of the following could be reasons for a surface that has an odor: If the previous homeowners or tenants were smokers, had pets, were victims of a fire or cooked strong smelling foods. What has happened quite likely is the walls themselves have soaked up and retained those odors. Using a high quality primer will not only seal in and eliminate odors but it will prevent them from returning as well.
If you ask a homeowner who didn’t prime over old smoke or pet odor, they will tell you almost always the smell returned. That’s because regular paint doesn’t have the right structure to keep those odors away permanently, primer is the way to go.
- If there’s a drastic change in color
You’ll mostly need to prime before painting when you’re going from a very dark color to a light color. Paint colors that are very saturated will show through lighter, less saturated colors. If you want to save yourself the hassle of several coats of paint (possibly four or five), prime over that hot pink before you put up that picture-perfect white. Often the most popular primer color to cover extreme colors or prepare the wall for extreme colors is grey. Studies have shown that it helps the human eye diffuse extreme colors.
You may also want to prime before painting if you’re switching between two very saturated colors. Saturated colors refers to the intensity of color, as the saturation increases, the color appears to be more pure. As it decreases, the colors appear to be more washed out or pale. A highly saturated color is rich and bright, while low saturation will veer towards a scale of grey. Priming the walls will help you get a better idea of how the new color is applying and covering. It can be helpful to ask your local paint store to tint the primer for you ahead of time (most are white), which can also help you gauge the effect of your new color.