Fibreglass bumpers constitute a large number of vehicle bumpers. Fibreglass is used over metal because it is cheaper and easier to repair. Repairing fibreglass is a task that most auto owners can easily do on their own. Most auto repair stores sell fibreglass repair kits that contain all materials necessary to repair all but the largest bumper damages. If the bumper has a damaged area larger than 1 foot long, it is best to take the car in for professional repair. However, any damage smaller than 1 foot is possible to repair right at home.
Sand the cracked area with a rough grit sandpaper to create a rough texture on the bumper. Sand slightly outside of the damaged area, about 2 inches outside on all sides. If the damaged area is larger than a small crack, remove loose fibreglass pieces and dispose of them.
Clean the area with ethyl acetate and old rags to remove all wax, oil, dirt and other contaminants. Wear rubber gloves to protect your hands from the harsh chemical. Work in a well-ventilated area.
Inspect the area to determine if a fibreglass patch is necessary or if resin alone will fix the damaged area. Typically, depressed areas and cracks larger than 4 inches long will require the use of fibreglass sheets to complete the repair.
Mix 1 part MEK peroxide into 9 parts fibreglass resin. Mix the resin over the damaged area with the putty knife. Press three or four sheets of fibreglass into the area, smoothing it out with the rest of the bumper.
Continue to add resin over the patch until the height of the new resin sits slightly higher than that of the surrounding fibreglass. Make sure there are no air bubbles inside of the resin while it is still wet. Pop any air bubbles with a sharp pin.
Layer cling film over the resin to protect it from dust and other contaminates while it dries. Allow the resin to sit for at least three hours.
Sand the area with an orbital sander until it meets the height of the original fibreglass coat on the bumper. Follow this sanding with a buffing using a rubbing compound and old rags. Continue to buff the area until it has a high-gloss shine.