How To Repair A Plastic Bumper Crack

How to Repair A Cracked Bumper

Car bumpers can crack for several reasons, but most commonly because the car has collided with something unexpectedly. A minor collision with a bollard or high kerb can cause a bumper scuff, bumper scratch or even a bumper crack. Most modern Original Equipment Manufacturer (OEM) bumpers are made from plastic with a steel reinforcement bar hidden in the centre, so the plastic bumper may easily crack if damaged.

A proper shop will repaint the whole bumper (get rid of stone chips, etc), others will repaint only the repaired area and blend it in with the rest of the bumper. When the plastic becomes pasty and begins to melt, gradually incorporate the Universal Repair Welding Rod. Weld the tear with the Universal Repair Welding Rod making sure that two small beads are formed on each side of the iron. Cut the Universal Repair Welding Rod at the end of the weld. Make sure the weld is even and well fused. Cut a piece of plastic from the package the tab repair adhesive came in to shape the adhesive. Support the bottom of the plastic using a spreader. Apply adhesive to the plastic, then lightly press the adhesive to the backside of the repair. Next, wrap the plastic around the tab location.

Bumpers that are cracked or dented can not only look unsightly but can also be a safety risk. Fixing damage to your bumper is imperative, as a cracked bumper can’t necessarily absorb impact as well as an undamaged bumper can. Find out more on why you should get your bumper repaired here.

Bumper repair over replace

A cracked bumper does not always mean that the whole bumper needs replacing. SMART car body repair specialists can often repair minor bumper cracks and scuffs, saving time and money.

DIY Bumper Repair Kit

In some cases, bumper scratches or scuffs can be repair at home, with a DIY repair kit. However, if your bumper is split or cracked, it is recommended that you speak to a professional. Attempting a cracked bumper repair with no experience could lead to further costly complications.

For step by step instructions on how to use a bumper repair kit, read our guide here.

Professional Bumper Repairs

Most ChipsAway specialists offer bumper repairs, either on your driveway, workplace or at one of our conveniently placed Car Care Centres. ChipsAway specialists offer professional and convenient cracked bumper repairs, which save time and the cost of a replacement bumper.

At ChipsAway, we specialise in SMART (Small to Medium Area Repair) bumper repairs, which means specialists don’t always need to replace or remove the whole bumper. Instead we conduct a highly focused bumper scratch, scuff or crack repair and blend the repair into the surrounding area.

1. Our specialists begin by cleaning the area, to access the damage.
2. Then the damage is repaired by heating, sanding or filling the bumper.
3. Once the bumper is repaired, the area is then primed and cured with a specialist heat lamp.
4. Once the damage has been primed, ChipsAway specialists mix the colour code in their mobile workshop using a spectrophotometer to ensure a perfect colour match.
5. The repaired bumper is then resprayed, lacquered and cured with heat lamps.
6. Once the repair is dry, the area is polished to ensure the bumper looks as good as new.

So, if you have a cracked, scuffed or scratched bumper, contact your local ChipsAway specialist today for a free no-obligation estimate.

How To Repair A Cracked Plastic Bumper Cover

The key to plastic repair is to identify the type of plastic being repaired and then by selecting the best repair method.

For automotive, such as bumper repairs, the information below provides tips for plastic identification followed by the recommended approach to repair.

Also, explore a general repair method that can be used on a wide range of plastics.

Plastics Type & Suggested Repair Methods

Repair Method A

When a hot welder touches urethane, you will see discoloration and some smoke as shown above

Urethane used for auto applications (also called PUR) is what is known as a thermoset material. It is made by combining two chemicals in liquid form in order to create a solid. It cannot be melted with a welder.

To determine if you are working with a urethane bumper, place a hot welder (make sure it is hot) on the back of the bumper. Urethane will turn to liquid and cause smoke and bubling. After the test area cools it should feel sticky when touched.

The method for repairing urethane is with an airless plastic welder using a process like brazing.

Area With V-Groove Damage

When preparing the repair area create a v-groove using a Teardrop Cutter Bit.

Instructions:

1. Align the outer tear surface with clamps for aluminum body tape. An Insta-Weld thin adhesive can also be used to tack the tear.
2. V-groove halfway along the back of the part with a 6121-T Teardrop Cutter Bit. Since the urethane does not melt, do not use a hot tool to melt the v-groove into the urethane.
3. Use coarse sandpaper (80 grit or higher) to sand the v-groove. Remove any paint around the v-groove to strengthen the surface.

1. Align the outer tear surface with clamps for aluminum body tape. An Insta-Weld thin adhesive can also be used to tack the tear.
2. V-groove halfway along the back of the part with a 6121-T Teardrop Cutter Bit. Since the urethane does not melt, do not use a hot tool to melt the v-groove into the urethane.
3. Use coarse sandpaper (80 grit or higher) to sand the v-groove. Remove any paint around the v-groove to strengthen the surface.

Melt Rod into V-Groove

1. Using the temperature setting on the Airless Plastic Welder set it to “R1” or “clear.” rod setting. Use the R01-01-03-NT Poluyrethane welding rod. Make sure that the rod comes out the bottom of the welders shoe melted and clear, not bubbling or discolored.
2. Hold the welder’s tip off the surface of the plastic. Melt the rod into the v-groove. Do not over heat the base material. Melt the rod on the surface. Note that the goal is not to melt the rod and the bumper together. YOU CANNOT MELT THE BUMPER MATERIAL.
3. Use more than 2 inches of the welding rod in the v-groove at a time. Remove the rod from the welder tip. Before the melted rod has cooled, go back over it with the hot welder tip and smooth out the weld. Caution: Do not over heat the base material.

V-Groove and Weld Opposite Side

When the weld on the backside cools off, repeat the v-grooving and welding process on the opposite side.

Grind Weld to Smooth Contour

Now, use the coarse sandpaper to grind the weld to a smooth contour. The urethane welding rod does not feather well, so cover with 2000 Flex Filler 2 epoxy filler to refinish completely. Grind the weld slightly flush so that the filler completely covers the welded area. Follow instructions for Step 4 filler application.

Repairing Torn Bolt Holes on Urethanes

On both sides taper plastic around the hold down to a point using a Roloc Disc.

Use 6481 Aluminum Body Tape to create a bridge across the torn mounting hold. Melt R01-03-NT polyurethane welding rod into the area. Drill out hold when finished.

Repair Method B

If a bumper is not made out of urethane, the most likely alternative is what is called thermoplastic. This type of plastic can be melted with heat.

The most common type of material is called TPO (also now called TEO).

• TPO: Thermo Plastic Olefin
• TEO: Thermo Elastic Olefin

TPO and TEO plastics are repaired the same way.

Repairing V-Groove Damage

1. Align the outer tear surface with clamps for Aluminum Body Tape. You can also use Insta-Weld adhesive.
2. Run a v-groove halfway along the back of the part by either melting a v-groove in by turning the tip of the welder at an angle or with a Teardrop cutter bit.
3. Remove any paint around the v-groove. Radius into the v-groove using a coarse sandpaper.

Melt the Base Material and Tie Rod Together

1. Adjust the temp. setting on the Airless Plastic Welder to the setting that matches the selected welding rod. The rod should melt cleanly without discoloring (note that nylon melts to a light brown).
2. Place the tip of the welder onto the plastic surface and going slow, melt the rod into the v-groove. Pull the welder toward you so that you will be able to see the v-groove being filled. Do not lay down more than 2 inches of welding rod into the groove at a time. Remove the rode from the welder tip and before the melted rod has time to cool down, go over it with the hot welder tip and thoroughly melt the base material and the rod.
3. To mix the materials it can help to press the plastic with the edge of the welder tip, then proceed to go and smooth the area out. Keep the heat on until there is a good mix between the base and the rod.

V-Groove and Weld Opposite Side

Once the backside weld cools down, repeat the welding and v-groove process on the reverse side.

Weld Opposite Side and V-Groove

If the plastic needs to be finished, grind the weld to a smooth contour using coarse sandpaper. Grind the welded area slightly flush so that filler can cover the area welded. Follow the manufacturer’s instructions.

Repair Method C

Method C involves the use of a material called Fiberflex. It can stick to any plastic substrate (called a hot-melt or thermoplastic adhesive.).

The air welder is used to apply the adhesive. It is used to repair TPO (most common plastic used in plastic auto bumpers).

Fiberflex can be used on many types of TPO and other plastics. If you don’t know what type of plastic you are repairing, it is worth experimenting with Fiberflex.

Method C involves the use of a material called Fiber Flex Flat Sticks . It can stick to any plastic substrate (called a hot-melt or thermoplastic adhesive.). The air welder is used to apply the adhesive. It is used to repair TPO (most common plastic used in plastic auto bumpers). Fiberflex can be used on many types of TPO and other plastics. If you don’t know what type of plastic you are repairing, it is worth experimenting with Fiberflex.

V-Groove Damaged Area

Align the outer tear surface with clamps or aluminum tape. Remove the plastic in a broad V-groove halfway along the back of the part with a die grinder and heavy-duty round cutter bit or round burr. The v-groove should be 1-1/2 inches wide. Put some “grit” in the plastic by using a low-speed grinder to grind the groove with coarse sandpaper. Remove paint around the area with a DA sander using 80 grit sandpaper.

Apply FiberFlex

Using an Airless Plastic Welder, set it to the highest setting. Then use a 6028RT Round Tip to melt the Fiber Flex welding rod on the surface. The ideal adhesion is created by pre-melting one side of the end of the rod, then flip the rod so that the melted portion sticks to the plastic. Cut the melted part of teh ribbon off using the edge of the welder tip. Spread the Fiber Flex into the v-groove.

Don’t melt the FiberFlex and the base material together. This process is best compared to brazing. When the FiberFlex cools on teh back, repeat the welding adn v-grooving process on the opposite side. Build up the FiberFlex higher than the surface (it can also be sanded).

Let the FiberFlex cool and then sand with 80 grit paper using a DA sander at low speed. Use finer sand paper to for finer finish. Add more FiberFlex or Flex Filler 2 epoxy filler for low spots.

Plastic Repair Method D

For this approach, Insta-Weld adhesives can bond on auto plastics, particularly SMC, polycarbonate and ABS. Aluminum Tape can be used to back up any holes.

Fixing Plastic Cracks

Spray areas to be repaired using Activator Sprayer.

Align and Assemble Parts

How To Fix Cracked Bumper

Use aluminum tape or clamps to hold parts. Apply a small quantity of Insta-Weld to crack or joint. The adhesive can be wicked into the crack. Use the thicker Insta-weld 2 if parts do not perfectly fit. Spray the Activator to cure the area.

How To Fix A Cracked Plastic Bumper Cover

V-groove and rough sand, then blow away any dust, all around the hole. After applying the Insta-weld activator, fill the hold with weld compound and a few drops of Insta-weld. After 5 to 10 seconds apply another coat of Activator. When ready, sand area or if needed for repair, the area can be drilled.

Repair Method E – Repairing Plastics with Two Part Epoxies

Fix Cracked Plastic Bumper

1. The backside of the repair area should be sanded with 50 grit or higher sandpaper. Groove the plastic to improve bond strength. Next, stand lightly with 80 grit sandpaper to improve adhesion.
2. Identify the plastic that is to be repaired (see table above for properties of different plastics). If PP, TPO or TEO plastic, apply Filler Prep Adhesion Promoter using a brush on sanded areas.
3. Use fiberglass reinforcing tape over the area that was damaged. If the damaged part is SMC, cut a piece of scrap SMC as a backing panel. The panel should extend 2″ beyond the damaged area.
4. Select a two-part expoxy adhesive that best matches substrate hardness. Good choices are:
5. In equal parts, mix the expoxy adhesive and apply over fiberglass reinforcing tape on the back of repair. Before handling, allow to cure 15 minutes. If working with SMC, apply a bead of SMC Hardset Filler to the backing panel. Before handling, allow to cure.
6. Sand the front of the area using 50 grit sandpaper or higher number coarse sandpaper. V-groove away from the tear. For a stronger repear, use a wider and deeper v-groove. Be sure to remove any paint in surrounding areas and radius into the v-groove with 80 grit in a DA. If working with PP or TPO, apply Filler Prep
7. Prepare by mixing and then apply the adhesive epoxy. Build just above the surface to allow for sanding. Wait 20 minutes for curing before sanding. If working with SMC, layer pieces of uni-cloth fiber glass coth in the v-groove. Be sure to use expoxy to wet the cloth.
8. Smooth and contour the suface use 80 to 180 grit sandpaper.