If you know a thing or two about painting, you understand the role primer plays. Primer ensures you get a quality finish by creating an undercoat for the paint to stick to.
The primer itself is paint that promotes the adhesion of various topcoats. In every professional painting job, primer always comes second after sanding.
Do you intend to paint over plastic? Are you wondering if it’s okay to use a self-etching primer to promote adhesion?
Well, it’s unfortunate that self-etching primer doesn’t work so well on plastic. As you will see later on, self-etching primer is formulated to be used on metal and fiberglass.
The self-etching primer will hold well on these surfaces and create the perfect undercoat for paint.
Self-etching primer sinks into plastic. If you try painting your plastic car bumper, you will notice that it sinks. This, therefore, makes it unsuitable for use on plastic.
If you are painting plastic and want to use primer as an undercoat, we recommend a plastic primer. Is plastic primer a thing? Yes, it is.
Many DIY enthusiasts don’t know about plastic primers. This is why they look up to self-etching primer when painting on plastic.
Plastic primer is formulated to work perfectly on plastic. Not only will it promote better paint adhesion, but it will also improve the finish of the paint job.
With a can of plastic primer, you can use it on about five car bumpers. That shows you how good an option it is.
Table of Contents
- Why Does Self-etching Primer Sink into Plastic?
- What is a Self-etching Primer?
- How Do I Paint Plastic Using Plastic Primer?
- Can I Use a Self-etching Primer on Shiny Plastics?
- Is It Okay to Use Adhesion Promoter on Plastic?
- Do Plastic Primers Address the Flexibility Issues with Plastic?
- Does Self-etching Primer Damage Plastic?
- What Happens If I Use Self-etching Primer on Plastic?
Why Does Self-etching Primer Sink into Plastic?
The chemicals used in the self-etching primer are to blame. By sinking, we mean that self-etching primer is absorbed into plastic.
When you use this type of primer on plastic, it won’t do its job because it will have been absorbed.
What is a Self-etching Primer?
Not everyone is a paint guru. Therefore, before we go any further, let’s look more closely at what self-etching primer is and which surfaces it should be applied to. Self-etching primer is a little bit different from a regular primer.
It etches itself onto a surface. By doing that, this type of undercoat prepares a surface for painting by making it rough so that a top coat can hold on fairly easily.
Self-etching primer works using a similar mechanism, such as sanding. What it does is create a surface for the paint to cling to. This special type of primer should be used on metal and fiberglass.
It shouldn’t be used on plastic. Individuals who have successfully used self-etching primer on metal or fiberglass are often tempted to use it on plastic, thinking they will get the same results. Unfortunately, the self-etching primer is absorbed by the plastic.
How Do I Paint Plastic Using Plastic Primer?
Now that we have seen that self-etching primer isn’t ideal for plastic, You must know how to use a plastic primer. Because if you don’t use it correctly, there’s a good chance you won’t be so happy with the results.
Before we get started, there is something you should know. Plastic is one of the most complex surfaces to paint. The smoothness of plastic makes it hard for paint to stick.
To worsen the situation, plastic contracts and expands depending on the surrounding temperatures. This can lead to cracking or flaking of the paint.
All these factors make painting plastic a headache. However, the above doesn’t mean it’s impossible to paint over plastic. You can still do it. Here is a step-by-step guide:
1. Clean the surface thoroughly. This doesn’t apply to only plastic but to all surfaces that are about to be painted as well. Grab a scrubber and dip it in a soap and water solution, then get to work.
Ensure that the plastic surface is spotless. Using the car bumper as an example. Plastic surfaces can be really dirty sometimes. And this dirt can make it impossible for primer and paint to stick.
2. Scuff the plastic with 200-grit sandpaper. Understandably, you may ask, why should I sand and use a primer? Don’t they both do the same job?
The benefit of doing both sanding and the application of primer is that it improves the quality of the project.
We have already mentioned how difficult it is to paint plastic. Sanding roughens up the surface and makes it easier for the paint to stick. Therefore, don’t skip the sanding process. After sanding, clean the surface with a damp cloth.
3. When you are done with the scuffing, it’s now time to prime. The best primer for this project should be one that is formulated for plastic.
There are many plastic primers on the market. Finding one shouldn’t be so hard. Spray plastic primers are the best since they are easier to use.
Spray it on the plastic and give it some time to cure. If you are going to paint several coats, it is advisable to go with light coats and give them time to dry.
4. After the primer has dried, paint the plastic and let it also dry.
Can I Use a Self-etching Primer on Shiny Plastics?
The biggest challenge with all types of plastic, including the smooth, shiny ones, is paint adhesion. The paint doesn’t adhere to plastic.
This is why people use primers. One of the most common types of primer, self-etching primer, often seems like a better choice to use on plastic.
However, you should know that self-etching primer doesn’t work on shiny plastic. It will dissolve and won’t help with improving paint adhesion.
If you want to paint on shiny plastic, we recommend using plastic primer. It is more capable of enhancing paint adhesion.
Is It Okay to Use Adhesion Promoter on Plastic?
Instead of using a self-etching primer, you are better off going with an adhesion promoter. Unlike self-etching primer, which only works on fiberglass and metal, with an adhesion promoter, you can use it on plastic.
The application process is relatively simple, and it can ensure paint holds on for longer on plastic, preventing peeling and flaking.
Please note that there are many adhesion promoters on the market. Research is crucial if you want to find the best option. The adhesion promoter is a general name for plastic primer. They both serve the same purpose.
Do Plastic Primers Address the Flexibility Issues with Plastic?
Without a doubt, plastic primers promote paint adhesion to plastic. Unlike self-etching primers, which get absorbed into plastic, these primers create a strong undercoat.
When we were discussing problems that occur when painting plastic, we touched on the flexibility issue. This is when plastic expands and contracts when exposed to varying temperatures.
The question is, do these plastic primers address the flexibility issues of plastic? There are some special types of primers known as elastomeric primers.
These comprise a flexing agent that allows the paint to be slightly flexible.
In that way, it can expand with the plastic and contract without flaking, peeling, or cracking. If you are working on a very soft plastic, you need to get an elastomeric primer.
It should do a much better job preventing paint on plastic from cracking due to expansions and contractions.
Does Self-etching Primer Damage Plastic?
If you have used self-etching primer on plastic in the past, you may be wondering if it has an adverse effect. Fortunately, the self-etching primer doesn’t damage the plastic.
Plenty of DIY enthusiasts have used self-etching primer on plastic and haven’t realized any damage caused. Therefore, there is no cause for concern if you have used it.
What Happens If I Use Self-etching Primer on Plastic?
The best way for us to learn is through mistakes. If you have an adventurous spirit and like to try things out for yourself, you can perform a practice test.
Get some old plastic that you no longer use and spray it with self-etching primer. The following is what’s going to happen:
1. The self-etching primer will be absorbed into the plastic. This has to do with the presence of chemicals in the self-etching primers, which sink when poured on plastic.
2. The second thing that will happen is that there won’t be any undercoat on the plastic. If you paint it, there will be nothing to hold the paint.
If you had at least sanded the surface, there would be a good chance for the paint to stick.
3. Because the undercoat will be weak, the paint job won’t last very long on plastic. After a while, it should peel off or start to crack.
You can avoid all the above by using the correct primer, which is made of plastic. Instead of sinking in plastic, these primers will create a layer of undercoat.
When left to cure, it can promote paint adhesion and ensure the final results are more than appealing. Things such as preparation and the quality of the paint used also contribute to the final finish.
However, the type of primer used on plastic plays a critical role in determining how well paint holds up on plastic.
When shopping for plastic primers, you should also look for paints designed strictly for plastic. You may have a hard time getting ordinary paint to stick to plastic.