Los Angeles Trade Tech student Donald Smith applies filler to our plastic bumper cover. Chrome bumpers made a quick exit from the automotive scene in the late '80s. In their place are elaborate, but flimsy, plastic covers hiding stamped-steel impact beams with a wide swath of Styrofoam sandwiched in between. Why? Cost, weight reduction, and ease of repair are the likely culprits. Plastic bumper covers are cheaper and easier to manufacture and replace in the event of an accident. Plastic bumpers are actually good for us do-it-yourselfers. They are really easy to fix if they get scratched, gouged, or broken, and you don't have to mess with expensive rechroming once finished. Check out how the students at Los Angeles Trade Technical College smoothed out a few rippled and cracked bumpers. How To Identify PlasticsWe found a great online resource for plastic repair procedures. Check out Urethane Supply Company-it has a great section on its website with charts listing the types of plastics used in automotive applications, how to identify them, and how to fix them. Surf over to urethanesupplycompany.com. PARTS LIST BRAND DESCRIPTION AND PART NUMBER PRICE 3M automix 5895 EZ sand flexible parts repair kit 2 13-ounce tubes $64.99 3M automix 5907 adhesion promoter 12-ounce can 22.99 Mini-Weld Model VI airless plastic welder 5600HT 249.95 One repair method is plastic welding. Using a tool similar to a soldering iron and plastic filler rod, you can fill holes or fix cracks like this. Plastic welding machines are available at auto body supply stores or through Eastwood Co. One repair method is plastic welding. Using a tool similar to a soldering iron and plastic To prep the bumper, grind away the paint and rough edges, then cut a V-groove along the crack on the front and back of the bumper. That gives the filler material more surface area to hold on to. To prep the bumper, grind away the paint and rough edges, then cut a V-groove along the cr This is the front-side V-groove. Clean the repair area with a plastic solvent and press the plastic welder to the edges of the crack. When the plastic begins to soften and melt, add some filler rod and melt it into the crack, spreading the excess material around with the flat part of the welder. Clean the repair area with a plastic solvent and press the plastic welder to the edges of The cool thing about this process is you can use a piece of the bumper you're repairing as the filler material. Cut a thin section off in an inconspicuous area and grind the paint off. You can use your bumper to fix your bumper and have no worries about mixing incompatible materials together. The cool thing about this process is you can use a piece of the bumper you're repairing as You can also buy plastic filler rod in a variety of different types of plastic to suit the different types of plastics you'll encounter in your car. Many plastic welder kits will include universal plastic filler rod, too. You can also buy plastic filler rod in a variety of different types of plastic to suit the Plastic repair, whether you're using a two-part filler material or plastic-welding method, is meant to go on thick and be sanded down to match the contours of the panel. So don't worry if you think your repair looks sloppy-it's supposed to. Plastic repair, whether you're using a two-part filler material or plastic-welding method, Sand the welded plastic with 80-grit, finish it up with 150, and you're ready for paint. A less expensive repair can be done on some plastics using a two-part epoxy filler material, saving you the cost of buying a plastic welder. The prep work is similar to the welding method. We brought the munched front bumper from our Crown Victoria for the students to work on. They began by grinding off the paint and frayed plastic pieces from the repair area and cut a V-shaped groove in the tear in the bumper. Next, the students pinged the bumper by drilling a series of holes on either side of the crack at regular intervals. These holes act like rebar in cement, adding yet another place for the filler to grab onto. A less expensive repair can be done on some plastics using a two-part epoxy filler materia Some plastics ooze chemicals that will repel paint and adhesives if not properly treated. The students thoroughly sprayed the repair area with 3M Automix 5907 adhesion-promoting spray, scrubbing the area with a Scotch-Brite pad instead of a shop towel. Then they clamped the bumper to hold it in place and applied mesh tape across the crack. This provides a substrate to hold filler material across the open areas of the crack. They filled in the backside of the crack with a rough application of filler. Once it dried, they removed the clamps to begin work on the front side of the bumper. Some plastics ooze chemicals that will repel paint and adhesives if not properly treated. The filler they used is 3M Automix 5895, a two-part flexible epoxy adhesive designed to repair TPO plastics. TPO stands for Thermo Plastic Olefin and is what many bumpers are made of. Our Crown Vic bumper is actually made of urethane, but this stuff worked just fine. The filler comes in two tubes. Squeeze out an equal amount of gunk from each tube and mix together thoroughly but quickly. It dries to the touch in only five minutes. The filler they used is 3M Automix 5895, a two-part flexible epoxy adhesive designed to re Auto body class instructor Brian Ferre spreads the filler on the same way you'd apply Bondo. For big repairs, use small amounts of filler and build up in several layers, allowing the stuff to dry between each layer. Don't try to fill a giant crack with a huge blob of filler-it's gooey stuff and won't hold its shape as it dries. The filler is ready to sand in 15 minutes. Auto body class instructor Brian Ferre spreads the filler on the same way you'd apply Bond Begin sanding with 80-grit paper on a sanding block to knock down the high spots and rough edges. If you need to add another layer of filler, clean the area again with adhesion promoter. Students Donald Smith and Raymond Anderson watch as Ferre shapes the filler to match a contour line in the bumper. Begin sanding with 80-grit paper on a sanding block to knock down the high spots and rough Finish sanding the repair with 150-grit. The bumper is now ready for primer. SOURCES Auto Body Tool Mart Elgin IN 3M 888-364-3577 www.3M.com Eastwood Co. www.eastwoodco.com Urethane Supply Company Rainsville AL Los Angeles Trade Technical College Los Angeles CA « | 1 | 2 | 3 | View Full Article By John McGann Enjoyed this Post? Subscribe to our RSS Feed, or use your favorite social media to recommend us to friends and colleagues!