According to manufacturers, primers and paints have very different jobs. Primers are designed to adhere to the substrate and create a uniform surface for the top coat. Primers penetrate and adhere to raw surfaces, evening up porosity so that the final paint film doesn't look blotchy. Primers for wood, whether they are latex or oil-based, contain specialized ingredients that top coats don't necessarily have, or have in lesser amounts. Stain-inhibiting tannin blockers or preservatives that are found in primers, for instance, are designed to soak into raw wood but not into finished surfaces. Primers for other surfaces have similarly specialized ingredients.Primers are available in oil, shellac, or latex-based formulas. Each type has differing properties and uses a different solvent for thinning and cleanup. Choosing which type to use is largely a matter of matching the primer’s characteristics to the project at hand.Varnish is a transparent, hard, protective finish or film that is pr