Increase the bonding surface by opening out the crack using a 3M Roloc Disc P80. For a crack reaching the edge of the panel, open the end to make a ‘V’ shape and remove plastic residue with a sharp knife.
Cut the 3M Instant Plastic Repair Patch 05888 to size (at least 2-3cm larger than the repair area) and place firmly over the entire crack on the back side of the bumper.