Ask the Expert Question-and-Answer Archive

by Ron Joseph

November, 2007

Flat Paint or Primer?

Q: Can you tell me the difference between flat paint and primer?  Will flat paint mark (stain) with water?  Or is that primer?  I hope this isn't a stupid question ... but I really don't know ...

A: A primer is the first coat of paint applied to a substrate, such as metal.  In the case of steel, galvanizing, aluminum, etc., the primer has two functions; to provide adhesion between the metal and the topcoat, and to offer corrosion resistance to the metal. Most primers are flat (non glossy) or they might have a semi-gloss appearance. It is unusual for a primer to have a glossy finish.

Topcoats primarily protect the primer and substrate from the environmental such as sunlight, rain, chemicals, solvents, abrasion, etc. Moreover, in most cases they are also used for aesthetic/ decorative purposes. and have a pleasing color and gloss.  Depending on the appearance you would like to achieve you might select a high gloss, semi-gloss or low gloss (matte, or flat) finish.

The chemical resistance, or in your question, the stain resistance of the paint depends on the type of resin used, such as acrylic latex, alkyd, epoxy, polyurethane, etc. If stain resistance is critical to you, then select a high performing coating such as a polyurethane, but be prepared to pay the high price.

Generally, low gloss paints of the same resin system tend to have poorer stain resistance than glossy paints. However, if you specifically do not want a high gloss or semi-gloss paint, you should select a flat paint that is advertised to have good stain resistance.

Generally, the higher-end consumer paints have better chemical resistance than their low-end cousins.  In other words, as a rule of thumb (this is not a scientific statement) the more you pay, the more you get for your buck.

Regards,

Ron Joseph