Using Plastic Body Filler - Part I
After you have appropriately, straightened the body part to be repaired, pried out dented areas, shrunk any high spots, and sanded off all paint and rust, it is now time to use body filler to repair the part completely.
Body filler has been used for many years to repair damages. The original body filler was solder, often called "lead" because of its high lead content. Today, plastic body fillers are used almost exclusively because you do not have to use heat to apply them, which reduces the chance of heat distortion, and because it takes relatively little skill to use plastic. Plastic body fillers are also less expensive.
All plastic body fillers regardless of who manufacturers them are similar in a number of ways. They come in two separate containers, one for the basic filler material and the other for the hardener. When you mix the two materials together, a chemical reaction occurs which causes the materials to harden. The hardener has a pigment, or color, which helps you determine how much you have added; the more color there is to the batch, the more hardener it contains.
When you mix filler and hardener, there are two things to keep in mind: the proportion of hardener to filler should be kept reasonable the same, and you should mix them thoroughly. It is best to follow the manufacturer's instructions. A lot of hardener means that the filler will dry rapidly, a little means the filler will dry slowly. Do not add so much hardener that you cannot work with the body filler; do not add to little because the filler may never harden.
Thoroughly mixing is also very important because if you haven't thoroughly mixed, after you have applied the filler, you may have to dig out filler that did not harden thus wasting time and energy.
Often, it may be an option to replace the panel or other part that has been damaged. But there are a number of advantages to using body filler instead to repair it. Many times it is more cost-effective to repair the part. Also, the original factory sealing, welds and rust-proofing remain intact if you repair the original part.
To mix the filler, remove a reasonable quantity from the can with a four-inch wide putty knife. Place it on a piece of sheet metal. Squeeze some hardener out of the tube. "Eye-ball" the amount you want to add. The amount you add is not that critical; it can vary to a degree. Experience will teach you the exact amount required.
With a back-and-forth kneading motion, mix the hardener into the filler. You can tell when the hardener is mixed thoroughly into the filler: the mixture will be uniform in color. Mix thoroughly - do not use a stirring motion but the kneading motion as described - to remove any air pockets in the mixture.
Tip: Do not use the same putty knife you used for mixing to remove filler from the can. This is because there is most likely some hardener remaining on the knife which will cause the filler to harden in the can eventually.
To apply the filler, see Using Plastic Body Filler - Part II.