There can be a lot of confusion around primers when it comes to painting a vehicle. Do I start with self-etch, urethane, or polyester? What do terms like DTM or 2K mean? Can I spray primer on top of existing paint or do I have to get to bare metal? These are all great questions, but there’s one that comes up more than any other.
When do I use epoxy primer and why?
To answer that, let’s start by explaining the roles of primer in a general sense. Regardless of composition or chemistry, primer’s job is to prepare a surface to accept a finish paint. It helps to create a smooth surface by filling in minor imperfections like scratches and pinholes. Primer also create a uniform foundation for a consistent paint finish, serving as a sealer between dissimilar materials.
Automotive primer provides a protective barrier against corrosion and rust, preventing moisture from reaching the metal surface. In the process, it also enhances adhesion between the base material the paint, ensuring it doesn’t peel, chip, or flake off over time. In short, primer plays a crucial role in achieving a desirable and durable paint finish.
Some primers are better at blending imperfections from the bodyworking process (urethanes) while others contain high solid content to act as liquid body filler (polyesters). Self-etch primers are intended to ‘bite’ into the base material for maximum paint adhesion. Among these self-etching primers is epoxy, which forms the base layer of protection to seal the substrate including any existing finishes. It is literally the foundation on which all your other process should be built.
Here’s when and how to use epoxy primer on your project:
Sealing Bare Metal
When working with bare metal surfaces, epoxy primers act as a sealer, preventing moisture and contaminants from reaching the metal substrate. This includes not only steel and iron, but also aluminum. In fact, it is often recommended to use epoxy primer on bare aluminum due to its excellent adhesion properties and its ability to provide a protective barrier against corrosion. Epoxy is a superior primer for bare metal, whether newly fabricated or something that’s had its previous finish stripped.
Filling and Leveling
Epoxy primers typically have a degree of filling and leveling capacities that help smooth out surface imperfections like dings, scratches, or light sanding marks. This makes them suitable for achieving a smooth and uniform base for subsequent layers of paint or body filler.
Sealing Dissimilar Materials
Because epoxy is compatible with metal, fiberglass, plastic, and most other paints and primers, it makes a great final sealer. By reducing it approximately 50%, you can spray out a thin, light seal coat before applying new paint.
Temporary Protection
Some of us drive our projects while we’re working on them or have to occasionally move them outside while we work on other stuff. A coat of epoxy primer can provide reliable protection on partially completed bodywork and bare metal until you can come back to finish working on it. In fact, for short-term coverage like that we like to use convenient aerosol catalyzed (2K) epoxies. Another alternative especially suited to temporary finishes is a roll-on version of epoxy primer like Eastwood’s Optiflow system.
@Andrew, while many plastic fillers will adhere well to bare metal, we recommend laying down a coat of epoxy primer first. Let the epoxy bite the metal, then let the filler adhere to the epoxy. Others will feel differently based on what they learned, but the current chemistry is designed for filler on top of primer.
thank you for the info on primers, with new different primers coming out, it is great to have a understanding on it use and what it is for.
this info is not on the can.
So one question that wasn’t answered. Should I apply plastic filler over epoxy primer or the other way around plastic filler on bare metal and then epoxy primer over it which is correct?
People have no clue what it really costs for materials especially the paint the reducer for paint and the clear when people would say why you charge so much I ask them do you have any idea what it cost for paint like a gallon they say about 150 dollars try the minimum of 8 hundred to 3 thousand dollars and does not include clear the reducer the hardner
So, if I am going to paint over previous paint (possibly from the 60’s) I should use self etching epoxy primer? This is mainly in areas that are to difficult to strip to bare metal (underneath hood,deck lid, interior cab, engine bay)
You should degrease and lightly scuff the EDP coating, but leaving it in place. No need to strip it.
When starting a paint job, can the epoxy primer be applied over the black (EDP) coating that comes already applied to replacement sheetmetal, or does it need to be stripped off first?
I think you should have mentioned that epoxy primer take a long time to dry. I believe they recommend at least 48 hours.
All good information, but it must be stated that epoxy primer is not very UV tolerant. Just like an EDP coating on replacement sheetmetal, extended time left in the sun will cause the coating to breakdown, correct?