Primer has many uses on automotive surfaces. It is responsible for paint adhering to metal and it protects the metal from corrosion. Without primer, the paint would peel and flake as soon as it starts to cure over metal.
These days, there are many types of primers and all of them come with different instructions. If you are interested in shooting primer over bare metal, you must know which will work and which won’t.
This is to help you avoid time and money. Our focus today will be on whether polyester primer can be used over bare metal.
Table of Contents
Will Polyester Primer Work on Bare Metal?
Polyester primer is the most controversial of all the primers on the market. That’s because there are many confusing details regarding its ability to adhere to bare metal.
When you read through the tech sheet of several polyester primers, the manufacturers claim that it will work on bare metal.
Other brands, such as PPG, are very clear that polyester primer should never be applied directly over bare metal. Instead, it should be used on epoxy primers, body fillers, and fiberglass.
If you have never used polyester primer and are probably considering doing so, the above information can be confusing and overwhelming.
After engaging in thorough research, we concluded the following. The ability of polyester primer to adhere to bare metal is a gamble.
Using information offered by different manufacturers and the varying experiences of other users, polyester primer can either stick to bare metal or decline.
This doesn’t have anything to do with the prep work, but it’s more because of the chemical composition of different polyester primer products.
As an individual interested in restoring your car’s paint job, you need to understand this. Polyester primer is meant to build and fill.
Unlike other primers, its main role isn’t to adhere to metal and seal it from other components. We can categorize polyester primers as general-purpose primers.
It’s precisely due to such reasons that you shouldn’t waste your time spraying polyester primer over bare metal. There are better products that are meant for this purpose.
If you must use polyester primer, spray something else over your bare metal and then use the polyester primer to fill up the surface.
What is Polyester Primer?
As we look into whether polyester primer can adhere to metal, we must define it. Polyester primer goes by many names.
It is known as a poly primer or spray-on body filler in most paint restoration shops. Over the years, polyester primer has become a popular product amongst DIY and professional painters.
One of the reasons polyester primer is a top choice in most paint jobs is its filling properties. Whether you have several tiny imperfections on the surface or minor pitting on metal, you can use a polyester primer to fill these up.
Polyester primer creates a uniform finish and works well over epoxy, body fillers, and fiberglass. Another quality trait of polyester primer is that it creates minimal shrink back on the surfaces it has been sprayed on.
And something experts can agree on is the straight finish provided by this primer. Polyester primer plays many roles. Unfortunately, being used to seal bare metal isn’t an area it succeeds very well.
What Primer Should I Use on Bare Metal?
If it’s your first time painting a car from scratch, the entire process might seem complex. But once you get the hang of it, things become much easier.
Having answered whether you can spray polyester primer over bare metal. You may be wondering what product I can use on such a surface.
Two main types of primers work wonders when used on bare metal. We will list them both so that you can choose which one is best depending on the situation you are currently in.
1. Epoxy Primer
Even if you have no clue about painting, you should have heard about epoxy primer. This is the number one go-to primer for all auto painting jobs.
People love epoxy primer because it adheres perfectly to bare metal and seals it, preventing the development of rust and corrosion.
Epoxy primer is often a non-sanding primer. You can spray it on, wait for it to dry, and then add other topcoats. Unlike regular primer, epoxy primer comes with the added advantage of protection against corrosion.
Rust is a common enemy among all car owners. Therefore, if you want to keep your car safe from such, it’s best to go with a product such as epoxy primer.
There are several perks of using this non-porous and high-bonding primer. The first is that you can use body filler over it. You can also use the polyester primer we talked about on top to fill in any dents and create a uniform finish.
Another reason why you should use epoxy primer is that it is compatible with a wide range of products. You can use it with almost anything, and it won’t start lifting.
Besides all these benefits, you should also know that epoxy primer costs more than typical primers. Epoxy primer, besides bare metal, can also be used on mixed surfaces and as a final sealer.
2. Self-Etch Primer
These days, self-etching primer is giving epoxy a run for its money because of the unique properties it contains. Self-etching primer is known for its quick turnaround time.
Just from what the name suggests, this type of primer etches itself to the surface of the metal and creates an unbreakable bond.
It dries pretty fast, and if you are in a hurry to paint your car, this is an excellent option. Self-etch primer also offers some corrosion resistance properties.
Similar to epoxy, self-etch primer comes with its fair share of benefits. First, this product is pretty straightforward. It doesn’t require a lot of prep work.
You are also assured of better adhesion and quicker curing times. Certain self-etch primers come with zinc phosphate pigmentation, which protects against corrosion.
Should You Give Polyester Primer a Try on Bare Metal?
Remember when we said that polyester primer could stick or fail to stick on bare metal? When you inquire from certain individuals’ they may praise how poly primer is perfect for bare metal.
This can tempt you to give the polyester primer a try. But before you do so, you may want to know more about polyester primers.
Polyester primers can be porous. This is one of the things that eliminate this product from being used over bare metal. A few decades ago, car manufacturers and owners weren’t cautious about rust.
Therefore, any primer would be used during paint jobs as long as it sticks to the metal. However, the porosity of polyester primer makes it a terrible choice because it will leak moisture into the metal, and rust will start to form.
If you live around the salt belt or are very cautious about rust, this characteristic of poly primer should make you think twice before spraying it over bare metal.
The other reason why you shouldn’t give the polyester primer a try over bare metal is that it may not adhere. Painting isn’t a fun project. It’s time-consuming and uses a lot of money.
Therefore, would you risk spending money and time applying a polyester primer over bare metal only for it to start peeling and cracking after a week?
That won’t be such a smart move. It’s better to stick to the recommended method of modern-day painting. Start with some epoxy, filler, and sealer then proceed to topcoats.
If you are old-schooled, you may want to go straight with polyester primer. But there are reasons why times change. It’s much better to use a primer that won’t waste your time and money.
Can Polyester Primer Be Used on Bare Metal for Long-term Projects?
You need to understand that we are not saying polyester primer is a terrible product. It’s an excellent filler and will create a uniform finish on a surface. We are against the use of poly primer on bare metal for long-term projects.
Polyester primer’s adherence to bare metal is a gamble. You can’t know for sure whether it will stick or fall apart. Secondly, the polyester primer doesn’t promise long-term results.
When used directly over bare metal, the primer is porous and will absorb moisture, thus leading to rust. Even if you get to stick this primer on bare metal successfully, you will have to deal with rust after a while. Therefore, it’s not worth it.
What Will Happen When You Paint Polyester Primer Over Bare Metal?
It’s wrong that some polyester primers write that it’s good for use over bare metal in their packaging and description. If you have no clue what polyester primer is supposed to do, such misleading information can cost you a lot of time and money.
Different car owners have had many terrible experiences when using a polyester primer over bare metal. The most common problem is that it comes off on its own through peeling or cheeping.
As if that’s not enough, the peeling usually begins after it has started curing. This means that the paint job won’t last for very long. There is also the rust issue.
If you want to avoid the aftermath of dealing with polyester primer, please don’t spray it over bare metal. Use epoxy or self-etch primer instead.