Plastic auto bumpers are good in that they do not rust. In addition, plastic features a lighter weight than metal bumpers, potentially giving the car better gas mileage. Fixing a cracked or dented plastic bumper requires a different technique than their metal counterparts. With flexible bumper epoxy and some power tools, you can repair the bumper's cracks. Do the repair yourself to save costly auto-body shop service fees.
Remove the bumper, or damaged panel of the bumper, from the auto. Most bumpers attach via a series of screws under the bumper and to the auto frame. If unsure of your car's locations, consult a service guide for that make and model. Use either a Phillips or flathead screwdriver depending on your car's make and model. Some autos have pinch clips and Allen screws as well, so use an Allen wrench if necessary.
Place the damaged bumper on a work bench and open the cracks further using the router. Take care to avoid cracking the bumper further. Make the edges of the cracks rough with the router, as the rough exposed plastic holds epoxy better than smooth plastic.
Sand down the area surrounding the crack with the sander on the backside of the bumper. The purpose of the sanding is the same as routing the cracks--to make the surface porous for the epoxy. Wipe away excess dust and debris from the sanded area.
Place masking tape along the crack on the backside of the bumper, bringing the bumper cracks together. The tape stops the epoxy from leaking around the back end of the bumper.
Add the epoxy down the line of the crack and hold for five minutes until the epoxy is tacky and holds the crack together. Let the epoxy dry as directed on the canister. Once dry, smooth it down with the sandpaper. Brush a coating of the clear lacquer to the cracked area to restore the plastic's lustre. Use the sponge brush to apply the lacquer, as it is a smooth application tool that will not mar the bumper surface. Put the bumper back onto the car.