Wash the bumper with a scuff pad and a car cleaner to remove any wax or grease buildup. Rinse to see whether the water beads up on the surface. If so, residue likely remains on the bumper. Continue cleaning until the rinse water runs off smoothly.
Sand the length of the front of the bumper with 80-grit sandpaper to remove the finish and create a textured surface.
Tape the bumper together if cracking has misshaped it, then sand the back of any damaged areas with 24-grit sandpaper. Blow the bumper clean with an air compressor.
Apply a thick coat of adhesion promoter to the back of the damage, and let it set for 10 minutes. While waiting, cut out a piece of wire mesh large enough to cover the damage and extend 2 inches all around the edges.
Squirt a bonding adhesive onto the back of the damage, spreading it with a putty knife, and then push the wire mesh piece into the adhesive. Apply another layer of bonding adhesive over the mesh to cover it completely. Let the adhesive dry before continuing to the next step.
Remove the tape, then scrape the front of the damage with a carbide burr to create a shallow ditch along the patched up damage. Blow away the plastic scraps with an air compressor, then apply a thick layer of adhesion promoter to the ditch. Let the adhesion promoter dry for 10 minutes. Fill the ditch with body filler, pressing with a putty knife to help air bubbles escape. Smooth the surface with the putty knife, and let it dry.
Sand the filled ditch with 80-grit sandpaper and then again with 180-grit. Blow the area clean with an air compressor.
Coat the front of the bumper with a flexible bumper sealer to promote paint adhesion.
Prime the front of the bumper with a flexible bumper primer surfacer, spraying evenly.
Spray a bumper color coat onto the front of the bumper, and let it dry. Once it has dried, wet-sand the bumper with 320-grit wet/dry sandpaper. Rinse it, and let it dry again. Repeat this process three times.
Spray the bumper with another coat, sanding with 400-grit wet/dry sandpaper to create an even smoother finish. After rinsing and letting it dry, spray the bumper once more with the final coat and allow 12 hours for it to dry.
