The art and craft of repairing with seam sealers and foams

Nov. 5, 2018
Look at these tips to confidently choose and use these materials for vehicle repairs and reduce noise, vibration, and harshness

Seam sealers and foams play an integral role to make vehicle repairs undetectable, but their proper application is important beyond just aesthetics.

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.

Repairers need to take advantage of the factory product being right in front of them. They need to take time to identify what’s currently installed, feel it to determine the softness or stiffness, and come up with a solution. If the OEM has not specifically indicated recommended repair products, it’s up to the technician to use good judgment and replicate the material as closely as possible.

For example, if a pad on the inside of a door skin needs to be replaced but is not available for purchase or there would be installation issues, an alternative such as an acoustic dampening pad from a local stereo/sound equipment shop could be used. This type of heavy pad is perfectly correct and is much better than doing nothing as long it does not negatively affect any kind of safety device.

Keep in mind that some of the “patches” found on the inside of panels are actually epoxy based fiber reinforced material which stiffens the panel and keeps them from "oil canning" or sustaining damage from say an operator leaning against the panel. These type of patches are often, but not always, included with service parts. When they are not included, additional effort is needed to complete the repair. If the panel is heated, there is often a point where the patch “softens” and can be removed. If it still has the same “shape,” it may be rebounded with an epoxy adhesive.

This repair stage, though, is also where some technicians may run into trouble. If they aren’t able to call a dealer and order the sound dampener, repairers may not know what steps to take next.

How to use flexible foam

Flexible foam (such as Fusor 121/124) may be used for sound deadening, sealing and filling door skins to the crash bar, hood panel to supports, trunk panel to supports, and the gas tank filler area. Flexible foam is compressible, unlike rigid- type foam. Here is a quick guide on how to use and apply it:

1. Remove any necessary panels and use a drop cloth to protect the surrounding area against accidental drippage.

2. Remove cap from the flexible foam cartridge and cut off the end of the cartridge tip.

3. Insert the cartridge into a manual dispensing gun. Note: Due to the thin viscosity of the material, a pneumatic gun is not recommended.

4. Gently squeeze out a small amount of material to ensure that foam freely flows from both ends of the tube.

5. Attach the mixing tip.

6. Apply a bead of flexible foam between the vibrating panels.

7. Avoid dispensing material too quickly. The foam will expand approximately 10 times its original volume to fill voids or eliminate vibration.

8. When sealing pillars or posts, apply a sufficient amount of flexible foam; approximately 1/3 of a cartridge may be needed depending on the size and configuration of the void.

9. Remove the mixing tip immediately after usage and install supplied cartridge plugs to avoid pressure build-up.

10. If desired, the flexible foam can be painted in 10 minutes

That’s why continual education on new alternatives and the latest options is so important. Repairing vehicles is no longer just a skill but also an art – and one that requires creativity. A sound dampening solution may be to take an existing product and adapting it to fit an application, but this requires technicians knowing what’s out there and how to be creative.

One auto manufacturer, for example, often has an NVH material in the vehicle body that is applied robotically as 1/4-inch strips of sealant very tight together. It's difficult to duplicate so artistry, skill, and experimentation become part of the equation.

One example is to take a threaded (a.k.a. “all thread”) rod and roll it on a mastic sticky pad. When warmed up, it becomes soft and pliable and can change appearance. It can also change appearance when it cools off.

This is the type of creativity it takes to fix cars and come up with new options. There are challenges, especially with NVH, if technicians don’t have the OEM’s “cookbook” of the “who, what, when, where and why” of everything on the vehicle. There must be careful decision-making when it comes to how to create NVH materials.

Technicians can reduce noise, vibration, and harshness (NVH) on metal panels with sound dampening material (such as Fusor 231/234) that provides a flexible seal without any shrinkage or read-through as shown on the right. A panel with read-through is shown on the left with a red circle.

Choosing and installing sound dampening and NVH materials are not like painting the hood of a car the wrong color. Even if NVH material put inside a deck lid or door doesn’t look absolutely identical to what was previously there, it is acceptable if it dampens noise without creating a problem – though some argue otherwise.

It’s not necessary to ensure that every non-visible paint marking that was present on the car during assembly is there, but rather that the vehicle is safe, functional, and has been restored to as-built levels of “noise” or “sound”.

Understanding product selection

Product selection matters in the repair. Choosing a product that is too stiff will result in read-through – each “dollop” will “ghost” (i.e. show through to the outside). Using a softer material, such as an NVH foam or sound dampening material, for a repair can alleviate this issue because it allows the outer panel some room to move.       

In addition to determining the proper type of material to use in a repair, technicians need to ascertain the amount of material to be installed, how to get the material to a specific location, and how to get the product to adhere in a specific area. Variables such as expansion, viscosity, and foam time also must all be considered.

Seam sealers and foam applications

Original equipment manufacturers (OEMs) use seam sealer and foam products in vehicle production for these applications. Collision repair facilities need to be able to effectively duplicate these.

  • 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 – Specially formulated sealers and foams are used to prevent various car parts from corroding.
To learn more, go to https://tinyurl.com/fusorrepairwithseamsealersfoam

It is important to note when choosing sound dampening material not only how well it reduces NVH, but its final appearance, work time, whether it will remain in position when applied on vertical or overhead surfaces, and versatility.

A sound dampening material that allows for extended work time may be needed when repairs will be prolonged and may be needed in multiple locations without causing read-through. For example, an NVH-reducing material (such as Fusor 231/234) can be used in applications including the roof bow and skin, door skin and intrusion beam, quarter panel and inner structure, and hood and deck lid skins. The black, urethane paste works well adhering to metal, the e-coat, and existing NVH materials but is also non-expanding and provides a flexible seal without shrinkage or read-through. These properties are essential to consider during the repair process.

Foam repair products used in collision repair are available in two-component formulations and two densities. Soft foams offer anti-flutter properties. Firmer, denser foams control airflow 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. These types are cured through a rapid chemical reaction instead of heat. The repair materials, Part A and Part B, mix together as they are applied and will begin to expand and cure almost immediately. The quick cure helps to speed up repairs. 

How to use rigid, acoustical foam

Rigid, acoustical foam (e.g. Fusor 130) can be used in vehicle pillars, rocker panel areas, and in other locations to promote sound deadening and reinforcement. This type of foam matches original equipment manufacturer (OEM) hard foam appearance (in the case of the Fusor brand) and does not retain moisture. With no cell structure, structural foam is a material with virtually no expansion.

Here is a quick look at how to properly use and apply the foam:

1. Remove any necessary panels and use a drop cloth to protect the surrounding area against accidental drippage.

2. Remove cap from the rigid, acoustical foam cartridge and cut off the end of the cartridge tip.

3. Insert the cartridge into a manual dispensing gun. Note: Due to the thin viscosity of the material, a pneumatic gun is not recommended.

4. Gently squeeze out a small amount of material to ensure that foam freely flows from both ends of the tube.

5. Attach the mixing tip.

6. Apply a bead of rigid, acoustical foam between the vibrating panels or dispense a stream of material to fill a void. Note: When filling voids, build a dam to locate the foam where desired. When applying to a vertical panel, dispense the material to the end of the tip. Allow the material to start foaming, dispense it slowly into the appropriate area. Applying this way will keep the foam from running down the panel.

7. Avoid dispensing material too quickly. The foam will expand approximately 10 times its original volume to fill voids or eliminate vibration.

8. When sealing pillars or posts, apply a sufficient amount of rigid, acoustical foam; approximately 1/3 to 1/2 of a cartridge may be needed depending on the size and configuration of the void.

9. Remove the mixing tip immediately after usage and install supplied cartridge plugs to avoid pressure build-up.

10. The rigid, acoustical foam may be painted in 10 minutes if desired.

To learn more, go to https://bit.ly/2n0J4v7

Sealers come in both one- and two-component formulations. Like its dual-component foam counterpart, two-component sealers also cure through a chemical reaction.

Single-component sealers cure through a moisture reaction. It’s important to note that one-component sealers, such as windshield urethane, will not attain a strong bond directly to metal and can cause read-through once the car is painted and delivered.

Direct-to-metal (DTM) sealers must be used for bare metal applications to achieve the best results and provide corrosion protection. Windshield urethane or hard seam caulk are commonly, though erroneously, used materials because they are generally in the body shop. These can cause read-through and are visible once a car has been painted and delivered.

Bare metal applications include floor plans, strut towers, core supports, core supports, trunk area, inner wheel wells, aprons, and door hem flanges. Most sealers require a primer, but there are several advantages to bare metal sealing such as the elimination of substrate primer, which improves cycle time and reduces costs.

This type of application also allows squeeze-type resistance spot welding (STRSW), which will weld through essentially anything, to be utilized – “weld bonding” when performed through adhesive and “weld sealing” when done through sealer. The sealer or adhesive will provide protection as it is not entirely destroyed by the spot welding process and encapsulates the weld nugget.

Repairers need to ensure the products they are using that are sold and promoted as NVH or sound dampening materials will hold position but are not so hard they will telegraph through and become visible. This will differ by area of the car.

The larger the vehicle panel – i.e. a roof or door – the greater the reason for using a soft product. On sectional areas such as the dogleg on the vehicle body forward of the rear tire, nothing should telegraph through because it is such a small space.

Keeping it quiet

Sound dampening – i.e. making the interior of a vehicle quieter – is accomplished by reducing the entry of noise through windows or other parts that are sealed off. This can be any cavity – such as pillars and rocker panels – that would allow noise to come through, directly transferring it through space and air.

“Sealers” keep out dust, fumes, and water and keep in HVAC. They reduce sound transmission – including most foams which are porous sealers – and provide corrosion protection in joints A cheat sheet to types of seam sealers and foams

Several types of seam sealers and foams are available to duplicate the appearance and performance characteristics of automakers’ production. Autobody shops should keep these various formulations in stock for repair work:

  • Controlled-flow seam sealers: These can be used on roof channels, door seams, drip rails, trunk seams, and truck-bed floor seams. These type of sealers cure quickly and are able to be sanded to a feather edge.
  • Direct-to-metal sealer/adhesives: This 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 that require a non-sag cosmetic seam sealer.
  • Flexible foams: This can be used for sound dampening, sealing and filling door skin to crash bar, hood panels to supports, trunk panels to supports, and the gas-tank filler area. It retains its memory without shrinkage and can expand to 10 times its size.
  • Rigid foams: These can be used in a vehicle’s pillars, rocker panels, quarter panels and floors, among other locations to promote stiffening, filling, sound dampening and reinforcement. They should match original equipment manufacturer (OEM) hard-foam appearance and do not retain moisture. Requires primer to be used. 
  • Self-leveling seam sealers: Use these seam sealers on drop rails, trunks, core support for aprons, roof seams and for a quarter panel to rear deck.

For original equipment manufacturer (OEM) approvals for Fusor seam sealers and foams, go to https://bit.ly/2mwU17p.

NVH materials – acoustic devices generally classified as sound-absorbing materials, sound-barrier materials, and sound dampening materials – are used both inside and outside a vehicle to eliminate noise.

Noise can come from sources such as the engine, driveline, tires, brakes, and wind as well as vibrations from the steering vehicle, seats, armrests, pedals, floor, and doors. It can also come through metal directly.

The key, when applying or installing sound dampening materials, is to duplicate what is found in the vehicle when making repairs. A substantial group of engineers initially put the vehicle together so there was a great deal of thought into the exact design. Remember, during the development of a new vehicle, there are hundreds to thousands of people designing and redesigning to optimize it. Each piece of metal, shape, weld, fastener, adhesive, and sealant, was chosen to perform a function and needs to be duplicated during repair as best possible. 

Automakers use quality products in their production lines, and they want the same product quality in the aftermarket. Customers want their damaged vehicles returned to them in as-built condition – not so parts look like they have been repaired or replaced. If a technician is repairing a door skin and finds 10 dollops of anti-flutter material between the intrusion beam and the outer skin, the same number needs to be put back.

What you need to know about proper storage of seam sealers and foams
  • Temperature: Must be kept between 60 degrees F to 80 degrees F.
  • Humidity: Urethane adhesives react with water – do not open foil bags unless planning to use.
  • Two-component materials:
    • Leave mixing tips on all partially used cartridges to seal, except for foams.
      Due to the expansion rate of the foams, the tip needs to be removed immediately after use to avoid the product from curing back into the cartridge.

As is standard with all collision repair estimates, the cost determined in the initial estimate to repair a vehicle to its pre-loss condition is preliminary. It can be likened to someone who is injured in a car accident or in a football game. Sometimes there are internal injuries that cannot be determined until a thorough examination or X-rays have taken place. The same is true for a vehicle. The cost to repair and the amount of damage is just a guess until the vehicle comes into the shop, has been taken apart, examined for any non-visible damage, and then “blueprinted.” This includes both aesthetic and structural repairs that would require the use of seam sealers and foams, including for noise and vibration.

After initial vehicle teardown, any additional damage not noted in the preliminary estimate should be included in the final damage report so an accurate repair plan/work order can be developed. This is where items such as seam sealers, foams, NVH material or special sound pads should be documented and added to the work order.

Any new noise introduced into the car after it has been fixed could destroy a vehicle owner's perception of the work done and implies a substandard repair job. Taking notes and photos during the disassembly process helps to ensure that it's not forgotten about and also allows technicians to bill for it.

Proper surface preparation

It may seem obvious, but it is worth reiterating that correctly prepping all surfaces is critical to proper vehicle repair.

Every repair procedure should begin with these steps: cleaning with soap and water, wiping with a water-based or solvent-based cleaner, using some form of abrasion to lightly scuff and give the material a way to adhere to it. Once these steps have been completed, the surfaces to be repaired are ready for the seam sealer or foam application.

Before applying a seam sealer or foam to bare metal – i.e. unpainted material – confirm that it is a DTM product. Otherwise, a coat of catalyzed epoxy primer needs to be applied to the surface to prevent a major corrosion problem.

Today, most one-part and two-part seam sealers are marketed as “bare metal sealers” and can be applied directly to bare metal – but always remember that if there is any doubt or fear of a products capability over bare metal, applying a coat of catalyzed epoxy primer and allowing it to fully cure will never cause a problem. Beyond this, any seam which may experience flexing should always be epoxy primed “just in case.”

Seam sealing and safety

Aside from improper surface prep causing corrosion or incorrect application, a poor repair job using seam sealers or foam can create far worse concerns than noise issues and detectable repairs. It can result in safety problems. Seam sealing is critical, especially to a vehicle’s air flow.

A poor job sealing off seams or leaving gaps in a panel could be a potential entry for not only sound or water (leading to corrosion) but also dangerous gases and fumes – i.e. carbon monoxide.

How to apply seam sealers

There are several methods for applying seam sealers. Here is a quick look at the various methods.

  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. Inner-seam sealer: The sealer is applied in the joint between panels; the sealer is then welded through by resistance-spot welding or the panels are held together by mechanical fasteners, such as rivets.
  3. Over-seam sealer: Applied over a joint to cosmetically hide or seal the joint.
  4. Liquid-Applied Sound Damper (LASD): A seam sealer applied to a panel to add mass or stiffen or create an insulating layer. LASD seam sealers can be applied by trowel or spray.

Note: 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 original equipment manufacturer (OEM) will apply a foam product to fill the gaps.

For more information, go to https://tinyurl.com/choosingseamsealersfoams

Vehicle HVAC (heating, ventilation, and air-conditioning) systems draw in air from the outside. Cars are designed with vents to allow air inside the vehicle to exit. The HVAC draws air in and blows through the car, with some of it leading out here and there. Depending on the age of the vehicle, the air circulation process may finish at the vent.

Exhaust could potentially flow to the windshield and get sucked back into the car. When driving, a vacuum exists that could potentially suck in air in all different directions – including where it shouldn’t due to a poor job sealing off seams or panels.

Following OEM procedures

Referencing the automaker’s vehicle-specific body repair manual as well as service bulletins will give technicians the necessary information on what products are required or approved.

OEM guidelines and repair procedures are set as the standard to ensure it is clear how to perform a repair to correctly fix the vehicle. Following an OEM’s Standard Operating Procedures (SOPs) for all aspects of a repair – which includes seam sealers and foams – will help ensure a vehicle both structurally and aesthetically is restored to pre-loss condition with a complete, safe and quality repair. 

Sponsored Recommendations

Best Body Shop and the 360-Degree-Concept

Spanesi ‘360-Degree-Concept’ Enables Kansas Body Shop to Complete High-Quality Repairs

ADAS Applications: What They Are & What They Do

Learn how ADAS utilizes sensors such as radar, sonar, lidar and cameras to perceive the world around the vehicle, and either provide critical information to the driver or take...

Banking on Bigger Profits with a Heavy-Duty Truck Paint Booth

The addition of a heavy-duty paint booth for oversized trucks & vehicles can open the door to new or expanded service opportunities.

Boosting Your Shop's Bottom Line with an Extended Height Paint Booths

Discover how the investment in an extended-height paint booth is a game-changer for most collision shops with this Free Guide.