Understanding plastic repair with adhesives

May 1, 2018
When considering options for plastic repair, shop management should carefully consider the cost of equipment and necessary training before investing in the next ‘cool tool’ for the shop.

Now that the collision repair industry has moved past the stigma of repairing plastic automotive parts rather than just replacing them, adhesives provide an economical and uncomplicated solution for technicians to make successful repairs. 

Each year, the collision repair industry is presented with thousands of plastic automotive parts that can be restored to original equipment manufacturer (OEM) standards – and done so simply and often profitably – rather than being replaced after they have been damaged. New simplified procedures of using repair adhesives for plastic repair provide an alternative to more cumbersome procedures – both past and current – that require intensive training and sometimes costly equipment.  

Repair adhesive products specifically formulated to be used on plastic for more than cosmetic repairs are offering straightforward solutions. For example, torn bumper tabs can be created with the plastic repair adhesive, enabling technicians to make a new tab, bond it to the assembly, and continue with the repair job. Emblems, headlamp modules, grilles, cladding, door trims, among other vehicle parts, can also be restored to “like-new” condition with repair adhesives when they are used properly, according to Kevin Creegan, Sales Manager for LORD Fusor Aftermarket Repair Adhesives in the U.S. and Canada for LORD Corporation.  

Although it can be helpful, there is no need for the vehicle repair technician to identify the type of plastic material – i.e. determine if the plastic material is flexible, semi-flexible, rigid or semi-rigid – just that the part is plastic. (It is generally required to determine if you are working with an olefin plastic to determine if adhesion promoter/surface modifier is required). As long as the technician selects the appropriate repair adhesive, while also following proper OEM recommendations, almost any plastic part can be effectively repaired with a repair adhesive, Creegan explains. Conversely, he adds, identification of plastics required for repairs made with a plastic welding can be both confusing and time consuming. (See diagrams, “Composite and Plastic Repair Process Using Adhesives” and “Composite and Plastic Repair Process Using Plastic Welder.”)

“Repairing a damaged plastic car part is as simple as identifying the damaged part and choosing the right repair adhesive,” he says. “With the right adhesive product, you don’t need to understand the type of plastic with which you are working. This really simplifies the repair process and saves time involved searching for mold marks, or in the case of plastic ‘welding,’ conducting multiple rod adhesion tests to match the substrate.” 

This is significant, especially as the use of plastic in vehicles continues to grow. Not only are automotive manufacturers staying focused on reducing vehicle weights – a.k.a. lightweighting – to comply with government regulations on fuel efficiency, but plastics and polymer composites continue to remain an integral part of vehicle safety and performance breakthroughs.  

The 14.65 million light vehicles assembled in the United States and Canada in 2016 – the latest available data, required nearly 4.9 billion pounds of plastics and polymer composites valued at $5.7 billion – $390 in every vehicle, according to the American Chemistry Council’s November 2017 report “Plastics and Polymer Composites in Light Vehicles.”  

By 2020, the average car will incorporate close to 770 pounds of plastics, up from more than 400 pounds in 2014, predicts analyst IHS Chemical in the report, "Weight Reduction in Automotive Design & Manufacture." 

A quick guide to successful repair of plastic vehicle parts with adhesives

Follow these guidelines when using repair adhesives to guarantee successful vehicle plastic repairs: 

Proper preparation:

  • Surface preparation – clean the front and back of the surface using the recommended cleaner 
  • Backing patch – a backing patch is required if the damage penetrates through the part, such as a bumper cover 
  • Sanding – for certain repairs use a sander or sandpaper to prepare the surface for proper adhesion 

Proper application:

  • Surface modifier or adhesion promoter – use the recommended surface modifier or adhesion promoter before applying the adhesive 
  • Equal mix – two-component adhesives require leveling of the plungers. Typically, a bead of adhesive should be dispensed through the mixer before it is applied to the repair area. 

Proper finish:

  • Curing times – Follow the manufacturer's suggested curing times to guarantee optimal repair adhesion. In some instances, parts may require clamping or taping during the curing process or the use of a heat gun.  
Sanding – Follow the manufacturer's recommended sand times to finish sanding the adhesive.


Staying on top of training

Since plastic used in vehicle manufacturing is obviously here to stay, training is crucial regardless of the process used to repair it. Although it may seem obvious, it’s worth continually reiterating its importance as well as emphasizing that procedure- and product-specific training is a must.  

“Any reservations about the use of plastic repair adhesives can be addressed with these few simple words and phrases: Training and Standard Operating Procedures (SOPs),” Creegan states. “If technicians experience problems with using plastic repair adhesives, it is usually because a technician is not properly trained and is not using the product correctly.” 

Adhesives Training Courses
LORD Fusor: For specific user instruction and technical data sheets for all Fusor Aftermarket Repair Adhesives solutions, go to https://www.lord.com/products-and-solutions/brands/fusor-repair-adhesives/user-instructions 

Making plastic repairs with adhesives is relatively simple, but it is important to understand the product being used and to carefully follow instructions to guarantee the best results. “It’s more than just pumping in a product to glue parts together,” Creegan emphasizes. “If the repair procedure is done properly the first time, the repair will last for the life of the vehicle.”  

Basic training is required to understand how to use adhesive plastic repair products, but body shop technicians can make repairs fairly quickly by following SOPs provided by the product’s supplier. At the same time, repairers need to ensure they are also adhering to vehicle maker specifications. Skill and precision are also important points to remember when using adhesive repair product. 

When dealing with plastic parts, urethane chemistry represents the best choice because it is flexible, strong and sands to a feather edge. “This doesn’t mean other adhesives such as acrylics and epoxies aren’t strong, but urethane adheres better to plastics including fiberglass, Kevlar, and carbon fiber,” Creegan points out. 

Consider equipment costs

When considering a new process or technique for repairing plastic parts, all components involved in that solution should be considered. This includes taking equipment costs into account as well as examining the cost of consumables such as cost of adhesive, costs for nitrogen gas tanks, and the high cost of replacing a membrane in a nitrogen “generator” contaminated by “dirty shop air.”  (Dirty shop air can also cause plastic repair failures, adhesive or welded.) 

Plastic welders require regular maintenance and many types of rods to fix all the different types of plastic, which regularly need to be updated and restocked. It’s also worth noting that welding is highly dependent on material compatibility, only like materials can be welded.  “ 

Equipment costs of plastic welders vary by manufacturer, but high-end models with a lot of bells and whistles can exceed five thousand dollars or more,” said Creegan. “The same amount of money invested in adhesive repair products would provide for enough material to last five or six years and allow for hundreds and hundreds of repairs to be made.  It’s also worth noting that adhesives require no capital investment and can be ordered just in time or as needed from the shop’s local paint distributor.”  

Polypropylene (PP), Thermoplastic Polyolefin (TPE) and Thermoplastic Elastomeric Olefin (TEO), the most common plastics used in vehicle construction, all vary in their characteristics as well as the temperature at which the plastic reaches a molten state for welding to occur.  If the temperature is too cold during welding, the material will not adequately flow together. If it’s too hot, it can cause material degradation. Most welding processes also require joint designs, which may be complex and difficult to mold.  None of these concerns apply to repairs made with adhesives. 

Circling back again to training, there is also necessary instruction that must be conducted on both the equipment and process for plastic welding. Training is very important for proper use of collision repair adhesives but requires several fewer steps than a plastic repair procedure that requires equipment such as a plastic welder. 

“In the case of a major equipment purchase, you get a shop demo and an instructor will be brought in for a day of training,” Creegan observes. “But where does the follow up training come from?  If a trained technician leaves a shop, who is responsible for training new technicians?   

To that end, it makes good business and economic sense to broaden shop offerings by using an adhesive solution for plastic repair. “Why not explore adhesive solutions offered by the local distributor instead of spending a few thousand dollars or more on a new piece of equipment that may end up eventually just collecting dust?” Creegan says, comparing the latest “shiny, new equipment” to a treadmill or other piece of equipment that ends ups as a clothing rack or just collecting dust. 

Don’t skimp on surface and application prep

One of the most important steps in the repair process is cleanliness. Technicians need to ensure the surface of the plastic parts to be repaired are thoroughly cleaned front and back using adhesion prep/cleaner specified by the adhesive manufacturer before starting the process.   

“Cutting corners on proper surface preparation can cause the adhesive to fail,” warns Douglas Craig, structural adhesives applications engineering manager & collision repair industry liaison for LORD Corporation. “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.” (Dirty shop air can also cause plastic repair failures, adhesive or welded.) 

Craig offers these tips to help collision repair technicians with proper surface prep: 

  • Thoroughly clean the surface! Preferably first with a surfactant (soap) and water then followed up with a cleaner specifically designed to remove waxes, silicones, and road “grease.” Do not allow cleaners to soak into the plastic, especially composite panels such as SMC or other FRPs. 
  • Make sure that all surfaces are dry before proceeding to the next preparation step.  
  • Backing patch: A backing patch is needed if the damage penetrates through the part, such as a bumper cover.  
  • Sanding and abrasion: Abrade the surface and apply a surface modifier, if needed. Scuffing the substrate with a scratch-pad, sanding with a variety of grit ranges, or grinding are all techniques that can create more surface area. An abraded surface typically has double or triple the surface area compared to the original flat, smooth surface but always be cautious to sand “slow” so the plastic does not “burn” or the bond will actually be weaker.  
  • Surface modifier or adhesion promoter: Use the recommended surface modifier or adhesion promoter before applying the adhesive. Surface modifiers and adhesion promoters must be fully flashed or cured. 

After completing thorough surface preparation of the part to be repaired, technicians need to make sure the adhesive itself is properly prepped. The ratio in a two-component adhesive cartridge is critical because it will otherwise be off ratio, Craig notes.  

“If the plungers are not leveled first, the mixture will be off ratio likely resulting in a failure,” he says. “You also need to purge a few inches of material from the mixer nozzle before beginning the application.” 

Warranty considerations

When deciding which process or combination of processes to use for plastic repair, warranty issues need to be considered. Adhesive repair manufacturers have their own product warranties. A plastic welder manufacturer also may warrant their repairs against failure, but typically their process requires adhesive to prepare the repair for the next step – refinishing.  

“This poses the question: ‘Who will warranty the complete repair when the process is a combination plastic weld and adhesive use?’” Creegan asks. “Adhesive manufacturers (using LORD as an example) will typically warranty repairs made using their material and process for the life of the vehicle. Does the manufacturer of a plastic welder provide the same across the broad spectrum of adhesives that can be used to make the repair ready for refinish?” 

Removing the guesswork

The best way to really understand and learn how to use plastic repair products – in addition to training, of course – is to work with a reputable supplier/distributor, advises Craig.       

“Selecting an adhesive takes the guesswork out of plastic substrate identification and repair process decisions,” he says. “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. “Repair adhesives give technicians the advantage of making repairs from beginning to end, and they know the upfront cost from a consumable asset,” Craig says.   

To learn more about plastic repair and to sign up for training, visit www.fusor.com and www.i-car.com.  

Look for Part 2 in this two-part series for an analysis of repair adhesives vs. other repair methods and what technicians need to know about using composite repair with adhesives. 

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