How can I prevent pinholing in body filler?

You’ve applied body putty or body filler to the surface of your car, but small holes and bubbles have appeared during the sanding process. When pinholes happen, they can be eliminated by applying and then sanding an additional layer of glazing putty.

In this article, I’ll answer common questions about how to prevent pinholing and eliminate it when it happens.

• What is pinholing?
• What causes pinholing?
• How can I repair a surface showing signs of pinholing?
• How do I prevent pinholing?
  
  

What is pinholing?

Pinholes (also called bubbles or air pockets) describe small blisters that break when body putty or body filler dries, creating tiny holes on the surface.

What causes pinholing?

Trapped air bubbles inside putty or filler are exposed after sanding a car, creating small holes or craters. There are three possible causes of pinholing:

• You incorrectly mixed your filler and hardener by using a “whipping” motion, causing air to be trapped inside the mix.
• You used too much hardener.
• You sprayed a coating that was too thick, producing too much heat. This resulted in gas bubbles forming inside the putty or filler as it cured.
  
  

How can I repair a surface showing signs of pinholing?

To remove pinholing from an affected area, follow these two steps:

1. Apply a thin layer of polyester glazing putty (properly catalyzed and mixed).
2. Sand smooth and continue the repair process.
   
   

How do I prevent pinholing?

Pinholing can be prevented by following these three tips:

1. Mix the putty/filler components by folding and pressing down on the mixture to eliminate air pockets.
2. Apply the putty/filler in thin coats. DO NOT exceed the manufacturer’s recommended total film thickness.
3. Always follow the manufacturer’s recommendation regarding the correct ratio of putty/filler to hardener.

By following these suggestions, you can prevent pinholing on the finish of your newly repainted car.