Priming and Sealing


What are primers and sealers?

A porous concrete slab having a sealer applied.

These two terms often get used interchangeably in the coating industry, but there is an important difference in the roles they play.

A primer is used for its adhesive qualities, meaning the next coat doesn’t have sufficient adhesion or is not compatible with the surface it’s bonding to. A common example would be using a primer before trowelling a dry mix of resin and sand. In this situation there’s barely enough resin to hold the sand together let alone provide a good adhesive layer and a primer would therefore be beneficial.

A sealer, on the other hand, serves the purpose of closing off the substrate before you apply the first coat. You can apply a sealer for a number of reasons, the most common being prevention of defects like pinholes.        

What are our top priming and sealing tips?

  1. Number of coats - another difference between primers and sealers is that you tend to only require a single primer coat whereas you can require multiple sealer coats. For example, you apply the first sealer coat and notice it looks glossy in some areas but bone dry in others. If I was concerned about defects on a decorative epoxy floor, I would want to see consistently sealed concrete across the entire floor before the basecoat went down.
  2. You don't always need to prime or seal - a big question that comes into play on this topic is whether you always need to prime or seal. In short, the answer is no. You can buy primerless products that are resin rich enough and surface tolerant enough to be applied directly onto the substrate, eliminating the extra labour and product required to apply a primer. If you’re lucky you can also get well-laid slabs that aren’t porous or powdery and won’t need a sealer to bring them up to scratch.

  3. No guarantee of better results - some people suggest priming or sealing on every job anyway, but doing so just for the sake of it isn’t recommended and there a many examples of where priming and sealing actually caused trouble. You’ve also got to make sure you used the right product and apply it correctly; otherwise you can end up making things worse for whatever system you put over the top. 

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