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Tips for Prepping, Applying, and Sanding Body Filler/Bondo

Posted by Ashley Schwab on

Automotive plastic body filler, often times called "Bondo," is used quite frequently for automotive repairs and restorations. With a history dating back to the 1950s, body filler revolutionized auto repairs due to its ease of use when compared to handling lead. Now, body filler is considered a superior option for fixing those small dings or holes or to smooth warped panels. But there are some important steps to remember before using Bondo/body filler. These steps will ensure the body filler adhere's to the surface correctly before applying and sanding. 

Prepping For Body Filler

First step: Prep the Surface
When beginning the process of using Bondo, make sure the surface that you will be working with is prepped correctly before applying. If you do not prep, the body filler will NOT stick to the surface well. Before applying, paint needs to be sanded to the bare metal. Make sure to sand outside of the repair area as Bondo will need to be spread and applied wider than the damaged area. (36-grit to 220-grit should do the trick for body filler application). sells a vast assortment of sandpapers and sanders to complete this step. 


Second Step: Blow/Wipe Off the Sanding Dust
The surface must be clean in order for the filler to adhere correctly. Wipe of the surface area until clean. 


Third Step: Measure The Surface Repairing  
Have an idea of how much filler will be needed in order to prevent continually needing to remix. This will also ensure consistent hardness. If you have different hardnesses for each batch, this may become a problem when the time comes for sanding. Likewise, mixing too much body filler ends up being wasteful and thrown away. Mix enough for 10-15 minutes of use. 



Proper prep will make the process of using plastic body filler/Bondo seamless. Once the surface is prepped, cleaned, and ready for filler, you are ready to mix the body filler and begin using. Applying body filler/Bondo takes proper application. 
To delve into prepping, applying, and sanding body filler/Bondo:




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