Commonly referred to by the trade name of “Bondo,” polyester body filler is used by autobody shops to achieve cosmetic repairs on automobiles.  It is relatively inexpensive, easy to work with, and achieves good results when used properly.  It is basically polyester resin that is highly filled to create a thick paste which can be turned into a solid with the addtion of a hardener.

I have been using autobody filler since age 14, and am finally getting good at it!  Just kidding.  It is more art than science, and practice makes perfect.  Basically, a surface needs to be properly prepared to achieve good adhesion.  Then the filler is applied after being mixed with hardener, and allowed to cure afterwords.  Some fillers can be sanded as soon as 20 minutes after application.

Basic setup and tools

Basic setup and tools

The basic setup is a working board surface to mix the bondo and hardener.  The mixed material is applied with a squeegee or putty knife to fill in low areas.  They also aid in cleanup, along with some paint thinner to clean the tools.

Hardener added

Hardener added

Mixing the read moreThe Ups And Downs Of Fruit Machine Games are often considered to be the easiest casino games to play. hardener starts the application window from where the material goes from liquid to solid.  The hardener is a peroxide paste that directly affects cure time along with temperature.  Too little hardener can also cause poor physical strength characteristics along with difficult sanding properties.

Uniformly mixed

Uniformly mixed

The hardener must be uniformly mixed before it is applied.  This prevents lots of problems down the road.

Applied to surface

Applied to surface

The body filler can be applied with putty knives or squeegees to achieve the desired affect.  This polyester bodyfiller will shrink during cure, so filling high is typical.  The flip side is that all of the high spots must be sanded back down, which is wasting filler and time, so it is a fine line to walk.

Working with body filler can be frustrating for the beginner who must practice lots of patience.  There are many important aspects that must be followed, just like all composites materials processes.  Autobody filler requires proper surface preparation, mixing and metering of materials, and attention to details in order to avoid future problems.

A couple of other practices I recommend is to always wear a dust mask, keep the body filler dry, and only apply bondo over sanded bondo.  Some like to just build layers without sanding the lows, and this can lead to adhesion problems.