The main objective for a collision repair shop technician is to restore a damaged car to its pre-accident condition. This will not only satisfy OEM and safety requirements, but will also guarantee customer satisfaction.
So, how do you return a damaged vehicle to its “as-built” condition? The answer is – “by using materials that are equivalent to the original manufacture.” You can use repair seam sealers and foams that duplicate the look and performance of the original OEM products.
The long-term safety of the vehicle is the most crucial point to remember when performing repair operations. A damaged vehicle must be properly sealed, corrosion protected and brought back to “as-new” condition to ensure the “crash-worthiness” of the car in three or five or seven years. Make sure you use the appropriate repair material in the right place to protect the longevity of the vehicle.
OEMs and NVH
Car manufacturers use seam sealers and foams to control noise, vibration and harshness/corrosion (NVH) almost anywhere in a vehicle body. OEMs primarily use one-component products, which cure during the e-coating process; however, two-component products are sometimes installed in the paint shop after the e-coating has been cured.
Typically, two-component seam sealers and foams are used in the repair process, since the heat system needed to cure a one-component material is not feasible for a repair shop. Two-component products/materials allow the repair technician to achieve the same quality or characteristics that are evident in the component being repaired.
Here’s how OEMs use NVH products in vehicle production:
· Noise control – Foams eliminate air movement in the auto-body shell; when air movement is curtailed, noise is reduced
· Sound and vibration dampening – LASDs (Liquid-Applied Sound Deadeners) are used to dampen vibration and noise in floor panels, vehicle underbodies and inner cabins
· Harshness – Sealers and foams are used to provide a “smooth” ride for the driver and the passenger by eliminating air gaps that can lead to a “bumpy” ride
· Corrosion protection – Sealers and foams that are specially formulated to prevent various car parts from corroding
While it is not possible to exactly duplicate the seam sealers and foams used in OEM production, the repair products that are available will produce equivalent results. This is especially evident with two-component seam sealers and foams used for repair vs. one-component OEM products. Different types or formulations of repair products can still provide the same outcome.
More often than not, an OEM will indicate that a sealer or foam has been used in a particular area of a vehicle, but they might not always describe the type of product or specify which product to use for repair. However, more and more OEMs are beginning to identify options to use as repair products.
Seam sealer or foam?
How then does a repair technician know when to use a particular seam sealer or foam? A repair technician should always begin a repair operation by reviewing the OEMs repair documentation to see if there is any indication given as to what products should be used for repair. The technician should next do the obvious – as you are dismantling a vehicle, look closely at the material that needs to be replaced. If OEM-recommended repair products are not specified, try to duplicate as closely as possible the material that you are touching.
| A seam sealer and foam guide |
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There are many types of seam sealers and foams available for duplicating the appearance and performance characteristics of vehicle OEM production. Here are some of the various formulations a collision repair shop should have in stock for repair work. · Rigid Foams – These can be used in automobile pillars, rocker panel areas and other locations to promote sound deadening and reinforcement. They match OEM hard-foam appearance and will not retain moisture. · Flexible Foams – Can be used for sound deadening, sealing and filling door skins to crash bar, hood panels to supports, trunk panels to supports and gas-tank filler areas. · Direct-to-Metal Sealer/Adhesives – Duplicates a factory appearance on standing seams, cosmetic seams, truck-bed seams, tooled door-skin seams, floor-pan seams, core-support seams, brushed seams, and other applications requiring a non-sag cosmetic seam sealer. · Self-Leveling Seam Sealers – Use on drip rails, trunks, core support for aprons, roof seams and quarter panel to rear deck. · Controlled-Flow Seam Sealers – Can be used on roof channels, door seams, drip rails, trunk seams, and truck-bed floor seams. These sealers cure quickly and are sandable to a feather-edge. High-Definition Sealers – These products will duplicate the look and function of OEM sealers, including sound-deadening material, wheel-house coatings and “swirled” seam sealers. They can be used on bare and primed metal as well as SMC and Fiberglass®. |
Another valuable source for repair advice is your jobber’s technical representative. The representative can help you choose the proper repair product that will closely match the OEM’s product, and can also supply repair procedure documents, instructional materials and user safety information.
Repair product selection
Foam repair products are available in two-component formulations and two densities. Soft foams offer anti-flutter properties; and firmer, denser foams control air flow and noise through vehicle cavities. The dense foams are used in any area where an inner and outer layer of steel can cause a noise path.
Two-component foams come in a cartridge formulation and cure through a rapid chemical reaction, not heat. The repair materials, Part A and Part B, mix together as they are applied and will begin to expand and cure within seconds. They cure quickly, helping to speed repairs.
Sealers are available in both one- and two-component formulations. Two-component sealers will cure through a chemical reaction; one-component sealers cure through a moisture reaction. Older technology sealers cured through evaporation of solvents. Certain one-component sealers, such as windshield urethane, will not attain a strong bond directly to metal. For metal-to-metal applications, use DTM (direct-to-metal) sealers for the best results and corrosion protection.
There are three methods for using seam sealers:
- Weld-through sealers – the sealer is applied in the joint between panels; the sealer is welded through by resistance-spot welding or the panels are held together by mechanical fasteners, such as rivets
- Applied over a joint to cosmetically hide or seal the joint
- LASD – Liquid-Applied Sound Deadener – a seam sealer applied to a panel to add mass or stiffen or create an insulting layer. The LASD can be applied by trowel or spray
In some repair applications, a foam product used in production can be replaced with a sealer, if the foam’s purpose was to close gaps between car panels. During car assembly, panels do not always fit together perfectly in order to provide the tolerances needed to build the car. In these instances, the OEM will apply a foam product to fill the gaps.
When Not to Use
Do not use a seam sealer if a structural adhesive or a crash-durable adhesive is recommended for repairing a vehicle. While “sealers” are technically “adhesives,” in general, they have much lower bond-strength and material-strength, and do not provide the robust characteristics of structural and crash-durable adhesives. Using sealers where adhesives are suggested could ultimately diminish the vehicle’s capabilities.
Do not perform MIG welding operations on or near the application of a seam sealer or foam. Some seam sealers/foams are highly flammable, including not only aftermarket products, but those used in OEM production. Do not apply seam sealer material within two inches of the joint to be welded. Since resistance spot welding does not have the danger of producing an arc as with MIG welding, resistance spot welding can be performed with a seam sealer or foam, although safety procedures should always be followed for any type of welding operation. Foams can be applied to a part and/or the adjoining area, after welding has been completed. Remember: Weld first; then apply the repair sealer/foam. In most cases, foams will be installed after panels have been permanently attached to the vehicle.
When the objective is to duplicate the appearance and performance characteristics of OEM manufacture, using the proper seam sealers and foams can help you reach that goal. Seam sealers and foams offer easy application, with quick-curing properties. The end result will be a repair that is done correctly and will garner customer satisfaction.
