Solutions Beyond Metal

Customer Challenge: What is the best way to ensure a plastic bumper tab rebuilt with 3M™ Super Fast Repair Adhesive, PN 04247 will adhere reliably to a bumper surface?

Technical Tip: Beyond proper surface prep – typically, grinding to a knife edge with a 3M™ Roloc™ 60+ grade disc and following with a 3M™ Cubitron II™ 80+ grade DA disc until a “fuzzy” surface is achieved – an established best practice is to drill several 1/8” holes at the base of the new tab near the edge of the bumper. This is commonly known as “pinning.” This will allow the adhesive to flow through the bumper and bond with itself for added strength – almost like creating a liquid rivet or bolt securing the replacement tab to the bumper. Also, always use an adhesion promoter such as 3M™ Polyolefin Adhesion Promoter, PN 05907 before adhesive application.

Customer Challenge: My shop has recently had several callbacks related to bubbling in plastic bumper repairs. We repaired all bumpers using 3M™ Semi-Rigid Repair Adhesive, PN 04240. What could be causing this bubbling?

Technical Tip: Maintaining clean surface areas is always important in collision repair; thoroughly clean the repair before any sanding steps. After sanding, only use clean, dry compressed air to clean the repair area. Solvents can be absorbed into the plastic and release over time, causing bubbles in the repair area. Additionally, the application of polyester based body fillers over some plastic repair materials can lead to bubbling. It’s best to follow 3M SOP and perform final filling over repair adhesives with 3M™ EZ Sand Flexible Parts Repair material.

Customer Challenge: Our shop has attempted to repair bumpers on several occasions, but we are experiencing problems. Either the repair is visible after the paint cycle or the bumper re-cracks during installation. What could we be doing wrong?

Technical Tip: A good repair starts with a good foundation, and surface prep is your foundation. It’s very important when repairing a deep gouge or a tear that goes all the way through the plastic to make a wide, gradual taper. A proper taper on the cosmetic side of a bumper should be deep enough to expose about ¼ inch wide strip of the patch on the back side of the part. Changes in temperature will cause the adhesive to expand and contract and pull away from the sharp edge of a “V” groove causing a ghosting line to appear. With a gradual taper there is no sharp edge where the plastic will separate from the adhesive. Also a “V” groove is too narrow for the adhesive to bond to.