A quality finish is typically not difficult to achieve if the proper materials, tools and procedures are used. Primers are used to fill voids in porous materials and seal the surface to allow the top coat paint to dry in proper manner. This allows the "cure" rate to be consistent so that the finish turns out the way it was designed to, rather than clouded, or with a less than perfect surface.
What is Epoxy Primer
In strictest terms, there is no such thing as an epoxy primer. A primer is a separate chemical compound from the top coat that goes over it. A priming coat of epoxy is made from epoxy thinned with a solvent to allow it to soak into the surface more and create a thin bonding coat. This coat protects the surface and gives the top coat the proper foundation it needs to create the best possible finish.
Pros of Epoxy Priming
When thinned with solvents, epoxy creates a very tight bond with the substrate. It creates a waterproof seal that is beneficial in stopping oxidation, particularly on metal surfaces. The tight bond created with the surface is strong and long lasting. If applied properly without runs and drips, epoxy primer coats do not typically require sanding, which cuts down on the application time of the paint finish.
Cons of Epoxy Priming
The same waterproof seal that is a benefit in many instances can create problems when using epoxy as a primer over concrete surfaces. Any surface that "sweats," or produces condensation, needs to breathe in order to dry. An epoxy primer coat will tend to bubble and may fail entirely in these applications. Epoxies as primer also cure slowly in colder environments, and may not have as smooth a finish when compared with surfacers.
Most residential paint jobs are primed with either latex- or oil-based primers. Both of these are designed for use on porous materials such as wood and drywall. In professional painting there are many other options. Two common types of primer used primarily in auto painting are enamel primers and self-etching primers. Enamel primers cure by oxidation and are easier to use, since they have no usable life limits and do not require an activator. Self-etching primers are typically two parts and are used extensively in auto body repair, due to the quick air drying speeds.