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Understanding plastic repair with adhesives

Tuesday, May 1, 2018 - 07:00
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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." 

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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?   

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