The first step in understanding if you need to use a primer before painting walls is knowing what a primer is. In this blog, we’re going to explain when and where primers are needed before painting walls.
We’re going to focus on four primary functions of Primers Sealers that homeowners and DIY painters are likely to encounter when preparing to paint walls.
What are Primers?
A Primer or Primer/Sealer is a preparatory coating that acts as a bridge between an incompatible or suboptimal substrate (material being coated, i.e. new drywall being painted) and the desired finish coating.
New drywall or Gypsum board that has been taped, mudded, and sanded requires a primer before being painted for best results.
The four primary functions of Primer Sealers
Equalize surface porosity (create an even surface for the finish coats of paint).
Adhere (stick, or bond to the substrate) to hard to paint surfaces like glossy Oil-based and Alkyd surfaces.
Seal various stains or bleeding wood tannins (naturally occurring chemicals in wood that may cause discolouration of the finish coating).
Cover dark colours with fewer coats of paint.
Major coatings manufacturers like Benjamin Moore, Insl-X, and Sherwin Williams have multiple waterborne low-VOC (volatile organic compounds) Acrylic Primers Sealers as well as various Oil-based and Alkyd Primers Sealers. What primer you should use will depend on what you are painting.
When priming walls isn’t necessary
Priming walls isn’t necessary for most applications. Most waterborne Acrylic paint is self-priming over primed and previously painted walls.
If you’re not sure if the paint you’re planning on using is self-priming you can check TDS (Technical Data Sheet) also known as the PDS (Product Data Sheet).
Technical data sheets for all of Benjamin Moore's coating can be found on their website. Sherwin Williams also has product data sheets available on their website.
When you should Prime walls
Walls should be primed when painting new Drywall or Gypsum board if the walls are stained, if they have been previously painted with a glossy Oil-based or Alkyd enamel paint, and when doing a drastic colour change.
Priming new Drywall and Drywall repairs
New drywall should be primed before painting with a Drywall Primer or a Multi-Purpose Primer Sealer. We also prime after using spackle to fill minor damage on walls to ensure an even finish coat.
Priming over stains
Before painting over smoke damage, water stains, ink, and other contaminants that aren’t able to be cleaned, and or that might bleed through the topcoat stain-blocking, we recommend using a Sealer or stain blocking Primer. Generally Oil-based and Alkyd primers are more effective for sealing stains.
Priming glossy Oil-based or Alkyd walls
Glossy Oil-based and Alkyd surfaces should be sanded and primed before painting to ensure that the finish coats adhere to the surface. Waterborne Acrylic, Oil-based, and Alkyd Bonding Primers work great when used over glossy, hard-to-paint surfaces.
Priming before painting dark colours
High-Hiding waterborne Acrylic Latex primer is great when doing a drastic colour change. When going from dark to light colours, using a Primer can lower the number of finish coats needed to achieve an even colour.