Another Bondo trick for large open holes you're too lazy or welder-less to
fill properly is to take a disc of cardboard slightly larger than the hole and
put a knotted string through a hole in the center. Turn the disc on edge to
push it through the hole and then using the string, pull the disc up against
the backside of the hole. While you continue holding the string, fill in the
open space with bondo and hold the string snugly to keep the cardboard backing
in place until the bondo firms up. Cut off the string and start sanding.
My dad showed me that trick when he made me patch the drywall I put my foot
through when my flying kick accidently missed my younger brother. This method
is only to be used on a car you plan to sell to a person you will definetely
never meet again.
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