What to know when repairing plastic anywhere on a vehicle

March 1, 2016
Plastic repair products are not just for bumper covers. Plastic repair products can be used for repairing any plastic part in a vehicle; however there are several important aspects to know when using plastic repair products, such as the plastic composition of the part, how to make the best repair, and how to work with the product supplier.

The first appearance of plastic in car design can be attributed to Pontiac’s Endura bumper that was introduced in the late 1960s. This innovative bumper featured a plastic-coated steel frame that was integrated into the decoration of the car. The bumper was strong and impact resistant, and launched the use of plastics in car manufacture.

Within a few years of the Endura bumper introduction, the U.S. National Highway Traffic Safety Administration (NHTSA) issued its first passenger car bumper safety standards in the early 1970s. These standards called for car bumpers that could better absorb shock and prevent serious accidents. The increased use of plastics, as a less expensive method for providing bumper safety, was pushed along by further NHTSA regulations in the late 1970s and early 80s.     

Now, almost 50 years after the first plastic bumpers originated, both non-structural and structural reinforced plastics are used almost everywhere in car body design. Some car parts, such as door-panel trims and body molding, are made with unreinforced plastics; and other parts, where strength is needed, are made of materials with added fibers such as fiberglass, Kevlar® and carbon fiber. As more plastics were used in automobile design, epoxy and urethane repair products were developed to repair the plastics. These products were simple to use and provided superior repairs.  

Repairing all plastics

However, plastic repair products are not just for bumper covers. Plastic repair products can be used for repairing any plastic part in a vehicle; however there are several important aspects to know when using plastic repair products, such as the plastic composition of the part, how to make the best repair, and how to work with the product supplier.

Reinforced-plastic damage (before repair)
This photo shows the damaged fibers.
Reinforced-plastic (after repair)
When repairing a fiber-reinforced part, it is necessary to use a plastic repair process that integrates reinforcing fibers to ensure a proper repair.

While many plastic repair products can be used on both non-structural and reinforced plastics, how does a repair technician know where to use them? The first step is to identify the substrate that is being repaired. Molded plastic parts should have an “identifier,” which can usually be found on the back or inside of the part. This identifier is an abbreviation of the plastic used in manufacturing – such as PP for polypropylene and PO for polyolefin. (Earlier plastic parts were not identified, as this is a recent implementation.)

The markings are designated by the International Standards Organization (ISO) to assist with plastics recycling and are used globally. Additionally, they are useful for identifying plastics for any number of reasons, including car repair.

Along with PP for polypropylene and PO for polyolefin, there are several other naming structures that are common to vehicle repair: ABS (acrylonitrile-butadine-styrene); PC (polycarbonate); PE (polyethylene); and PVC (polyvinylchloride). There may be polymer blends used in parts manufacture as well, and these are marked with both plastics, such as PC+ABS (polycarbonate and acrylonitrile-butadine-styrene).

If you cannot find the identifying mark on a part, check with the OEM for help in classifying the type of plastic used. While many plastic repair products are formulated to work with any plastic, a technician still needs to know if the plastic is fiber-reinforced, otherwise the repair could fail. Knowing if the substrate is fiber-reinforced or non-reinforced has more to do with the repair procedure than with the particular repair product.

Making plastic repairs

Plastic repair adhesives can be used for cosmetic repairs and/or internal restorations. Cosmetic damage refers to nicks, gouges and other minor surface defects that do not penetrate the material. Damage to the fibers or damage through the composite panel can also be repaired, but with a different procedure than a cosmetic repair.

Interior repair refers to any repairs that are not on the surface of the vehicle. These parts can be visible or totally concealed, such as headlight mounting tabs or mounting bosses on door trim panels. Urethane adhesives can be used to “build” new mounting tabs that are as strong and robust as the original piece. (See sidebar) 

A significant cost savings can be realized when using plastic repair products. A repair done with a plastic repair product can be considerably less costly than purchasing a new part. Moreover, if done correctly, the repair could be undetectable. Besides the cost savings advantage, there is also a time-savings benefit, since a repair can be made almost immediately versus waiting for a new part to arrive. Taking into account time, cost and labor savings, using plastic repair products can be a big boost to a collision repair shop’s bottom line. Customer satisfaction should not be overlooked either, since a fast, guaranteed repair can get a vehicle back on the road more quickly.

Unreinforced substrate (before repair)
This photo shows structural damage to unreinforced substrate.
Unreinforced substrate (after repair)
When application instructions are carefully followed, plastic repair products will produce a Class-A finish on all automotive plastics.

Know the procedures

While there is some basic training required to understand how to use plastic repair products, repairs can be done fairly quickly by following the standard operating procedures (SOPs) provided by the product’s supplier. Skill and precision are important points to remember when using urethane products. It’s not just pumping in a product to glue parts together and the job is done. If the repair procedure is done properly the first time, the repair will last.

It’s crucial to follow the instructions given with the repair product. Some products will require an adhesion promoter/surface modifier for bond strength, but there are also products available that will bond directly to the substrate and, in some instances, will eliminate a step. Although getting a vehicle repaired quickly is certainly a goal for meeting customer needs, skipping steps in the repair procedure is not the answer. If you skip steps, you may not have the perfect solution to a repair and you could

Plastic repairs—you can do bumper tags

Plastic repair products can be used for more than just cosmetic repairs. Torn bumper tabs can be recreated from the plastic repair product. Instead of buying a new part, you can make a new tab, bond it to the assembly, and continue with the repair job.

Here are some tips for repairing a torn bumper tab. (Remember to consult with your supplier for specific instructions related to the product you are using to make the repair.)

• Hand-sand the area around the torn tab; blow away any debris.

•  Apply a surface modifier to both sides of the damaged area; let it dry.

• Use bumper reinforcing mesh to prepare a reinforcing patch.

• Apply the plastic urethane repair adhesive to the tab repair area on the bumper.

• Wrap the pre-cut mesh around the tab area and squeeze together.

• Apply a thin, smooth coat of adhesive to the outer surface.

• Allow adhesive to cure per product recommendation.

• After the adhesive is cured, drill a mounting hole to simulate the original tab.

• Refinish the tab according to paint manufacturer’s instructions.

have a customer dissatisfied when the repair fails. 

One of the most important steps in the repair process is cleanliness. Make sure that all the plastic parts that will be repaired are thoroughly cleaned before starting the repair. Cleaning can be done with prep/cleaner products specially formulated to remove all waxes, silicones, dirt and road oils. Dust and debris can be removed with compressed air.

Know the differences

As noted earlier, although it can be helpful to identify the type of plastic used in a part, many repair products only require that the technician recognize if the plastic is reinforced or non-reinforced. While the repair process is different for reinforced or non-reinforced plastics, the key points for making a repair are the same.

Repairing fiber-reinforced plastic parts such as hoods and fenders will take you down a different repair path than non-reinforced plastic parts. The fibers contained in the plastic change the plastic’s density. Sometimes, a part is not 100 percent plastic; it might be 80 percent plastic and 20 percent of another material (added for strength).

When a repair is made on a fiber-reinforced part, the repair process must simulate the same basic panel construction or density. It’s important to use a plastic repair process that integrates fiberglass to ensure a proper repair. If you use a repair process that is not fiber reinforced, at some point the repair will show read-through. The dissimilar materials (repair product and substrate) move around at different rates through heat and cold cycles, and eventually the repair may become noticeable as a shadow or crack.

The best way to understand and learn how to use plastic repair products is to work with a reputable supplier. Select an adhesive that takes the guesswork out of plastic substrate identification. There are products on the market that can be used on all plastic parts whether they are flexible, semi-rigid or rigid. Having to use just one product for all types of plastics reduces the complexity of a repair and reduces inventory.  

A supplier’s representatives should also be able to provide documentation SOPs, instructions and hands-on training, so that all the technicians in a collision repair shop use the same procedures for repairs. Training is critical to obtain long-lasting repairs that are quick and cost-effective.

Repair vs. replace

Some collision repair shop technicians are hesitant to fix plastics – they may believe that it is complicated to use plastic repair products, or they may think the repair will not hold. Neither of these circumstances is true, and if technicians experience problems with using plastic repair products, it is usually because a technician is not properly trained and is not using the product correctly.

So, instead of repairing a plastic part, the collision repair shop will replace the part. But this is an unnecessary and costly solution, and certainly will not save time in getting the vehicle back to the customer. Used parts are not the answer either, since they can be more costly than using a plastic repair product. More often than not, a broken plastic part that is fixed with a plastic product actually provides a better and stronger repair than using a non-OEM replacement part.

Again, always follow the SOPs and keep these key points in mind when performing a repair procedure with plastic repair adhesives:

•          Cleanliness is paramount. Use soap and water first on the damaged area, and then a cleaner to remove silicones and other contaminates.

•          Taper all repair edges to avoid read-through.

•          Use surface modifiers/adhesion promoters where directed.

•          Install reinforcing fiber when repairing fiber-reinforced plastics, and use reinforcing mesh when making structural repairs to non-fiber-reinforced plastics such as bumper covers or plastic tabs.

•          If uncertain on how to make a proper repair, contact the manufacturer or contact the manufacturer’s representative.

When application instructions are carefully followed, plastic repair products can produce a Class-A finish on all automotive plastics. They are easy to use, cost-effective and can return a damaged vehicle to as-new condition in a short amount of time.

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