Understanding repair product selection for seam sealers and foams in collision repair

by Douglas Craig, Technical Application Engineer & Collision Industry Liaison, Structural Adhesives Tech Service, LORD Corporation

When using foam repair products and seam sealers in collision repair to restore vehicles to pre-accident condition, a repair technician needs to understand when and how to use these materials.

Douglas-Craig-edited photo

Douglas Craig

A repair operation should begin with a review of the OEM’s repair documentation to see if specific products are indicated for repair. The technician should look closely at the material that needs to be replaced while dismantling the vehicle. If the OEM has not specified recommended repair products, try to duplicate as closely as possible the material that you are touching.

Foam repair products used in collision repair 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. 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:

  1. 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
  2. Applied over a joint to cosmetically hide or seal the joint
  3. 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.

Learn more about seam sealers and foams for collision repair by reading, “Restoring vehicles to pre-accident condition with seam sealers and foams.”

For a video on using seam sealers in collision repair, click here.

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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.

 

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