Drill a hole of 4-6mm in diameter at the base of the crack in order to release stress and prevent further extension of the crack.
Prepare the area around the crack using a 3M Hookit Abrasive Disc P80 (for hard plastics) or P180. Avoid overheating and melting the plastic.
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.
Clean the area using 3M VHB Surface Cleaner or 3M General purpose Adhesive Cleaner 08984 applied with a 3M Professional Panel Wipe 34567.
To achieve maximum adhesion use 3M Patch Adhesion Promoter 06396 to the back side of the repair. Allow 5 minutes to dry.
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.
Spray Polyolefin Adhesion Promoter 05917 on the front side of the bumper around the cracked area. Allow 10 minutes to dry.
Using 3M Applicator 08190 apply 3M Flexible Parts Repair Material 05901 to the cracked area.
Spread and smooth 3M Flexible Parts Repair Material 05901 into the crack and allow to dry for 20 minutes.