Careful bodywork is required to properly prepare body panels for painting. Bodywork repairs sheet metal and removes all traces of rust. Bondo fiberglass putty is useful for filling in small dings and scratches in a car's body. Holes and rusted-out spots require the use of fiberglass mats soaked in resin to cover larger, more extensively damaged areas. If you don't have the skills and tools to cut and weld sheet metal, repairing with Bondo, resin and fiberglass mats is an inexpensive and easily accomplished alternative.
Prepare a rusted hole or puncture in the car for body repair by using metal snips to cut off the thin, badly rusted metal bordering the hole. Make sure you get it all. Sand around the hole with a rotary power sander to remove rust and paint from the hole's perimeter. Continue sanding until the surrunding bare metal is shiny and rust free. Tap the edges of the hole with the rounded end of a ball-peen hammer until it points slightly downward.
Mix up enough resin to fit the size of the repair job. Add 12 drops of hardener to each ounce of resin and stir it up in a plastic container. Cut a piece of fiberglass mat with scissors to completely cover and overlap the hole's edges. Put on rubber gloves. Place the mat in the container and submerge it in the resin. Hold it down with a wooden paint stick until the mat is thoroughly soaked.
Use automotive masking tape and paper to cover and protect the tires and body around your work area. Brush a coat of liquid resin around the edges of the damaged area with a paintbrush while the mat is soaking. Position the resin-saturated fiberglass mat over the hole and coat it with an ample amount of resin. Smooth the mat with the brush to remove wrinkles and air bubbles. Put on a second mat if the hole is still concave after the first mat has firmed up.
Let the resin impregnated fiberglass mat dry thoroughly. Sand the repaired area with a rotary sander using 80-grit paper. Keep sanding until the surface is smooth. Prepare the Bondo body putty with hardener-catalyst according to the directions on the container. Keep the mixture in the proper proportion. Stir the filler paste to a consistent texture on a flat plastic palette. Mix up only enough Bondo as you plan to use immediately.
Apply thin coats of Bondo to the affected area with a flexible plastic applicator. Fill in all low spots. Feather out the edges of the filler. Sand the area smooth between coats after the body putty has dried. Sand all the way to the edge of the Bondo patch to eliminate ridges. Continue to apply coats and sand until the area is smooth enough to primer paint. Wipe the surface down with a clean tack cloth to pick all dust and particles.
