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When to Use Direct-to-Metal vs. Standard Seam Sealers

( 02/05/2021 ) Written by: Douglas Craig

The seam sealer you choose for your repair is tasked with providing a robust level of corrosion protection while bonding metal surfaces together. The tough, flexible material duplicates the factory appearance on automobile repairs and industrial heavy-duty truck, bus and trailer repairs. You may be using seam sealers on trunks, truck bed seams, tooled door skin seams, floor pan seams and core support seams.

There are two sealer types currently in use in the repair industry. Repair shops can use Direct-to-Metal (DTM) seam sealers or a two-component (2K) primer and a standard seam sealer. 

DTM seam sealers, as the name implies, are applied directly to the metal surface without the need to use a primer beforehand. Since a primer is not necessary for these sealers, they are often used when the highest corrosion protection is not needed as would be provided when 2K primer is applied first. Still, DTM seam sealers generally bond very tight and protect the underlying steel or aluminum. Don’t be concerned about using DTM seam sealers, as the majority provide a high level of protection.

The 2K primer and seam sealer method is used by many repair shops as it does provide a better repair. If you are using a primer, don’t forget to factor it in the overall repair time. It may not be noticeable if it is planned as part of the process. If you are considering which product to use, note that on an exposed seam, a quick epoxy prime with a seam sealer is preferred. Exposed seams are those exposed to environmental influences, such as salt splash off the road. 

It’s always recommended to consult the material manufacturer’s guidelines. They include procedures that are the most robust for the best product usage and repair. It’s important to note that despite what procedures a material manufacturer may recommend, in the end defer to the OEM if the OEM has a published procedure to follow. It’s their car, they engineered and built it, so they know how to fix it.

When it’s time to make the repair, it’s essential that the technicians understand the entire process for the repair. With any of these products – DTM or standard seam sealer -- it's critical that the technicians fully understand these steps on how the product is to be applied, this includes:

  • Knowing how to tool it
  • How to get the correct appearance 
  • If there are any other recommendations for tricks or techniques
  • Reviewing technical data sheets and any SOPs
  • Reviewing the safety data sheet to understand what they're handling


When the technicians have all that information, then the process just becomes an art form.

Making the car appear just as it was before the accident is the end game. To ensure compatibility and the best result, it’s important that the shop is always testing off metal from the car with their own paint system. This is especially vital when using a slower curing material.

One last point: DTM sealers work well over 2K primers so don’t think they must be applied directly to bare metal. Use the sealer that “feels” the best for the outcome and appearance desired.


Douglas Craig

In his structural adhesive technical service role at LORD, Doug is responsible for providing guidance and repair solutions to repairers, OEMS and insurers which incorporate the proper materials and methods. Doug's previous role, as the Collision Repair Manager at Fiat Chrysler Automobile, was focused on all topics related to collision damageability and repairability.

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