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The art and craft of repairing with seam sealers and foams

Monday, November 5, 2018 - 08:00
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Seam sealers and foams play an integral role to make vehicle repairs undetectable, but their proper application is important beyond just aesthetics.

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With the sheer number of seam sealers and foams now available, it’s also essential that collision repair technicians understand how seam sealers and foams work — and how they should and should not be used.

A collision repair shop technician’s goal is to restore a damaged car to its pre-accident condition, which fulfills both original equipment manufacturer (OEM) and safety requirements as well as satisfies the customer. To return a damaged vehicle to its "as-built" – a.k.a. “pre-loss” or “pre-accident” – condition, repair shops need to use materials that are equivalent to those used by the original manufacturer.

Spray application of seam sealer can be applied as a surface coating to large areas of a vehicle as a durable treatment, which resists stone impingement-causing surface corrosion and also provides a sound deadening solution.

It is important to remember that when high-volume vehicles are being produced at the assembly plant, the sealants used are generally applied in the “paint shop.” Most OEM paint is called “high bake,” indicating that it must be cured with temperatures in the 300-degree Fahrenheit range. These same ovens which cure the various paint applications also cure the sealers and other NVH materials such as patches and liquid applied sprayable dampers (LASD), which can be added to panels as an application of mass to reduce noise.

Creating a heavy layer – the thicker the layer, the less sound that can come through – will diminish or eliminate noise. Liquid applied spray dampers, liquid applied sound dampers, liquid applied sound deadener, and liquid applied spray deadener are all just different terminologies for the same process – applying a layer of material to dampen sound transmission.

Note that those foam pieces found in pillars and similar locations have some type of a plastic “carrier” and are known as “blockers” or “poppers” depending upon what they really do. They are activated – i.e. caused to foam – in the hotter e-coat ovens. Along with these heat-activated products, there can also be two-component cavity filling foams and one-component sealers installed after the paint process. Also, low-volume specialty vehicles may be entirely produced with room-temperature curing products.

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 apparent 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.

Seam sealers and foams are used in body shops for their ability to provide a reliable seal and keep out moisture, but if applied incorrectly, just the opposite occurs. Moisture is instead trapped inside, causing corrosion. They have also become important for their use in sound dampening for noise, vibration, and harshness (NVH) issues.

Protecting against corrosion

When seam sealer is used on hem flanges – found on closure panels such as a door, hood or lift gate – the application is to prevent corrosion and to provide cosmetic aesthetics.

A spray-applied seam sealer can be tooled to create a different appearance.

Technicians should begin a repair procedure with a review of the OEM's documentation to see if specific products are indicated for use. Although it may seem obvious, it’s worth repeating – and then repeating again – that technicians should always follow OEM repair procedures and specifications for restoring corrosion protection. Adhering to the specified proper corrosion protection specifications using seam sealers, adhesives, and foam fillers will result in a complete, safe and quality repair. Failure to do so can cause a repair to prematurely fail.

Finding and using alternatives

If the vehicle manufacturer has not specified recommended repair products, the technician should closely examine – not only looking but also touching – the material that needs to be replaced while dismantling the vehicle.

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