Most everyone knows what primer is but not necessarily when to prime. Let’s look at three types of primers. Stain blocking primer, adhesion primer and a general sealing primer and when to prime various surfaces.
Stain blocking primer is used of course for stains. Stains like water stains, smoke, rust, tannin. They can also be used for things like marker or crayon. Normally anything that will bleed through the top coat. In almost all cases you are better off using a solvent based primer. Regardless of the stain, I suggest a quick sand to scuff things up a bit and then two coats of primer. Allow adequate dry time between coats. You should have no difficulty with the top coat.
Adhesion primer is used on difficult to paint surfaces or as part of a coating system. We use an adhesion primer when painting cabinets. We may also use a stain blocking primer when we have tannins bleeding through the cabinet surfaces. Adhesion primer would be used for example on tile, ceramic tile, plastics, etc.
General sealing primer is most often used when you need to seal a surface before painting. For example, repair work to drywall. You would want to seal the new drywall repaired areas before painting so you have a nice uniform surface prior to painting. If this is not done you will most likely see the areas that were repaired after painting. Especially with higher sheen coatings like semi-gloss.
It is not uncommon to see primers that use all these terms interchageably. You may find a latex drywall primer that claims to also be a stain “killer” or an adhesion primer that is labeled as a stain blocker as well. Many of these products may or may not work as advertised or that claim to work if you put enough coats on. As a general rule, I suggest using specific primers for specific tasks.
A great adhesion primer is zip sand. It’s thixotropic. Which means it’s very thick but becomes less viscous as you stir it or agitate it. It really sticks and sands beautifully.
A very good stain blocking primer is BIN primer. It is a shellac based product. Which is the “big gun” in the stain killer world. If BIN wont seal a stain you have a problem. Occasionally a top coat won’t like the alcohol base BIN is made in and the top coat will wrinkle. It doesn’t happen often but if it does then Cover Stain is a good choice.
Speedhide Maxprime is a good latex wall primer for drywall repairs or new drywall. No need for an expensive “primer” for drywall/repairs. The more expensive products don’t perform any better. Often on drywall repairs, a dead flat latex paint will suffice for priming those areas before painting.
Knowing when to prime is easy compared to navigating the vast number of products out there. The three products above will cover most any priming need you may have.