The Purpose
Primer surfacer is the final step or your final chance to produce the perfect surface with the correct texture before painting. Scratches and small imperfections can be repaired with this fill primer. Filling is the main purpose of this type of primer, you can think of it as a final filler. We finished the body filler or glazing putty with 150 grit, feather edged, cleaned the surface, masked, applied two coats of epoxy, and now we’re ready to apply primer surfacer.
Flash and Window Times
After the epoxy has been applied, you can now apply the primer surfacer. Be certain to allow the epoxy to flash the recommended account of time. The manufacture procedure page will tell you how long of a flash time needed before top coating. With PPG you need to let it flash at least 30 minutes. However, you also have a window. This is the time that you have to apply another coat without sanding. Most epoxies have a long window time. The epoxy that I am familiar with has a 72 hour window. If you wait more than 72 hours to apply the primer surfacer, it must be lightly scuffed to ensure proper adhesion.
Adhesion – Mechanical vs Chemical
I keep talking about adhesion. I would like to expand on this and tell you why this is important. Adhesion is just another word for stick-to. For instance, in upcoming lessons we will refer to glue as adhesives. In order to prevent body filler, primer, paint, etc, it needs to adhere to the surface. There are two ways to provide adhesion. The first is a mechanical adhesion. This is why we sand the surface before we apply the coating. That is why it is so important to sand the edges extremely good. If a panel is going to peel, chances are it will start peeling from an edge. The second type of adhesion is chemical adhesion. This is when there is still a chemical bond with two products. For example, the 72 hour window with the epoxy primer is the time the surface will produce the chemical bond. After that, the chemical bond will no longer adhere. That is why after the 72 hour window, the surface will need to be re-sanded. Since we no longer have the chemical adhesion, we now have the mechanical adhesion to takes it’s place.
Applying The Primer Surfacer
Alright, I took a little rabbit trail, but I wanted to make sure that you understand flash times, window times, and the types of adhesion. Now, let’s talk about applying the primer surfacer. After the epoxy has flashed of the recommended amount of time, apply your first coat of primer surfacer. Only apply enough to cover the epoxy primer. Check the procedure page to determine the recommended number of coats needed to achieve the desired thickness or mills. Normally, two – three coats are sufficient. I usually apply two wet coats allowing each coat to flash off. Apply each addition coat a few inches past the first coat.
What’s Next?
We’ve applied epoxy primer to provide additional adhesion and corrosion protection. Then we applied primer surfacer to fill the minor scratches and small imperfections. Now we’re ready to apply guide coat and block sand the primer. We’ll discuss that in another article.
By Donnie Smith