Recreating a tab with a "living hinge

Many times you'll see bumpers that have a flexible tab, usually at the bottom of the bumper. These tabs have a "living hinge", which is a thin line in the plastic where it naturally wants to flex. These living hinges are very weak and are easy to tear. You can't repair it at the hinge line because it won't be flexible there anymore. To do this, you need to recreate the tab using our polypropylene sheet using the following method.

Trace out the tab in the polypropylene sheet. If you have the old tab, lay it down on the 5010 polypropylene sheet and trace the edges and any holes with a marker. Put a dotted line where the hinge line is supposed to be. Then create a notch back into the bumper about 1/2 inch (1.25 cm) deep and extend the tab about 1/2 inch (1.25 cm) on each side of the tab. Cut the tab out of the PP sheet with a jigsaw, and drill out the mounting hole.

Create hinge line. To create the hinge line, put the tab in a vise and fold it back and forth several times along the dotted line you drew on the tab. Take it out of the vise, then fold it over double a few times to make it more limber. This is flexible and much stronger than the original bumper’s hinge. If there’s a hook or fold in the tab, you can create it by folding it in the vise one time.

Notch back the bumper. Place the new tab in position on the bumper and mark the cut line on the bumper with a black marker. Cut out the notch with a jigsaw.

Prep the bumper by removing paint and applying sanding scratches the bumper on the backside.

Tape the tab in position using 6481-1 or 6485 aluminum tape on the outer surface.

Weld the backside of the tab using the R02-04 or R02-05 profile PP rod. Start by focusing the stream of hot nitrogen about 1/2 inch (1.25 cm) beyond the tab until the bumper turns glossy. Stab the rod down and start making your pass using the same technique as described earlier.

Prep the outer surface by grinding a shallow v-groove about 3/8” wide along the seam. Feather back paint and put down some sand scratches with 80 grit in a DA. Blow dust free.

Weld the front side of the bumper with the R02-04 profile PP rod. Lay one strip down along the long seam, then weld each end and wrap the welding rod around the edge. If you have an airless welder, you can melt and burnish everything down and make it easier to sand flush.

Let cool and finish the repair by sanding smooth with 80 grit in a DA. Use filler if necessary to fill out any low spots, then sand with 180 and 320 grit to prepare for primer.

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