Auto Foam: Application

Auto Foam: Proper Application and Placement

Foam is showing up all over the modern vehicle. Although its presence adds a new level of complication to repairs, it’s imperative that it be reinstalled — and reinstalled correctly.

Being a collision repairer for the vast majority of my life, I never imagined that I’d be fascinated by foam – in an automotive sense, that is.

Whenever an overabundance of foam has appeared in my beer glass, it would bring about a general sense of being taken advantage of and change my attitude toward the barman, to the extent that when I asked for the “same again,” I’d request that, “This time, decapitate the head.”

Other than that, my feelings toward foam were pretty benign.

Sure, I knew foam had something to do with getting a good night’s sleep and getting all comfy driving down the road, but I really wasn’t involved with foam in an automotive collision repair sense, nor did I imagine I ever would be. So I was blindsided when it began to show up all over the modern vehicle.

It really shouldn’t have surprised me that much because I’d been seeing different materials stuffed into waterproof bags and then packed into the inner quarter panel areas, which reduced the drum-like quality these large voids produced. This was the
first NVH material (noise, vibration, harshness) and really dampened down the hollow, echoing sound that made an automobile less-than-a-pleasure to be in when driving down the road trying to appreciate Swan Lake on your classic FM station. These bags of textile material, packed snugly between adjoining parts, went a long way to control NVH, but that was just the feeble beginnings of what has become an important concept in the production and supply of the modern automobile.

Foams initially replaced textile materials because they were lighter, odorless, readily available, inexpensive, waterproof in their closed cell form and durable. They’re also adaptable in shape, strength, weight and cell structure to applicable needs. Actually, it’s an ideal material in its many forms and has a multitude of uses, which include:

  1. Controlling NVH.
  2. Strengthening the body structure to prevent flexing or twisting.
  3. Supplying added safety for the vehicle occupants in case of collision damage.
  4. Supplying predictable collision energy management.
  5. Allowing vehicles to be lighter to achieve fuel efficiency mandates while maintaining the safety of a much heavier automobile.

These are some powerful attributes for such a humble material.

Types and Uses of Foam
Foams come in several configurations and structures, depending on their intended use.

• Preformed Energy-Absorbing Foam — We’re all familiar with this type of foam. These parts are supplied by the OEM and may be purchased as replacement parts. They’re commonly found in bumper systems and replace the expensive, heavy systems that used massive steel bumper reinforcements and hydraulic or gas shock/energy absorbers. Set-in-place foam blocks are made of the same material and are commonly found in doors and some quarter panels.

If this type of foam is simply broken and not deformed or crushed, it may be repaired simply by gluing. Ford and General Motors both recommend repairing broken impact absorption foam with hot melt glue. Check the OEM’s recommendations. Repairing makes sense because these parts don’t derive their strength from shear or tear strength, but from the ability to absorb energy. Most of these simply sit on, or in, another part and are covered and held in position, so there’s absolutely no loss of strength in gluing a broken energy absorption foam part.

• Filler Foam — This type of foam has several consistencies and intended uses, and some of the same type of foam is known by different names.

• Rigid Foam/Semi-Rigid Foam/Pillar Foam — These three descriptions are basically the same type and consistency foam. Don’t be confused. It’s almost like shopping for a mattress. From one brand to another, the descriptions are such that comparison is difficult. In the automotive foam world, rigid, semi-rigid and pillar describe automotive foam not within the same brand line, but across the multitude of producers.

In other words, one manufacturer’s rigid foam may be replaced by another’s semi- rigid, or yet another’s pillar foam.

The purpose of this foam is multifaceted. It has a closed cell structure in its cured and unshaved or uncut state. It won’t absorb water unless it’s cut, shaved or shaped with a blade. If this is done, the area affected should be sealed with a urethane sealant to prevent water absorption. This will come into play in the application process, where some cured material oozes out of an opening or hole and must be cut to properly allow attaching parts to fit. Simply apply a low-grade urethane sealant to this shaved area and brush in to assure thorough sealing of the open cells.

Rigid, semi-rigid and pillar foam should NEVER be used in place of structural foam. The name rigid may be misconstrued to have a structural use, but this would be a serious mistake and compromise the structural integrity of the vehicle. Be aware!

These types of foam have limited chassis reinforcement capability. They can expand up to 10 times their liquid or cartridge state and can be used to block air movement, reduce noise and control the movement of body parts. In other words, they can control two or more adjacent parts from rattling against one another. Even though they’re not considered a structural component and should never, ever be used in place of structural foam, rigid, semi-rigid or pillar foam may be used to minimize a vehicle’s twisting or flexing capacity. If you were to simply leave it out, you could seriously affect the designed durability and stiffness of the vehicle. It should be considered deficient to do so.

This type of foam has a visible cell structure, permanently deforms if compressed and must be sealed if cut.

• Flexible Foam — Unlike the preceding foam, this foam has little confusion connected to it. It has many uses, which include filling large voids, blocking air movement, sealing water leaks, controlling sound by absorbing it and preventing panel flutter.

It’s often found when you remove a top, between the crossbeam and the top panel, between the door skin and the intrusion beam, between the quarter and inner wheel house, in any pillar, the fuel system filler pocket and anywhere two panels are in close proximity but the manufacturer doesn’t want them touching.

Flexible foam is a tremendous sound dampening material. It also prevents flexing panels from contacting each other and, if compressed, easily springs back to its original pre-compressed position. It’s closed cell in its cured
state but, if cut, must be sealed to prevent moisture absorption. If detached in the panel replacement process, it
can be reattached by the use of a urethane adhesive. Expansion rate can be
1 to 10.

During a recent frame rail repair job on the rear of a Mazda Miata Roadster, I observed the use of flexible NVH foam at the attaching location for the upper strut nut and shaft. Of course, this vehicle is very small and the driver’s head is not more than three feet from this location. The foam was used in this scenario to quiet the action of the strut to the body. Hmm … sometimes these guys amaze me.

• Structural Foam —
Structural foam is intended to reinforce and strengthen the structure of the automobile and manage collision energy forces. It can be found in the torque box area of full frame vehicles, pillars and front lower rails. It can also be used between engineering changes.

“What’s that mean?” you ask. Well, maybe the OEM realizes that the vehicle is structurally deficient in some way, but before they can make changes to rectify that deficiency, they’ve got a few thousand parts to use up. So they enhance the strength through chemistry.

Structural foam is definitely tough. You can dispense it into a cup and, when it’s cured, drive a pickup onto it and see absolutely no distortion or deflection. Leaving this out of a repair procedure would seriously and definitely compromise the repaired vehicle’s structural integrity.

While it has a closed cell structure, you can see it with your naked eye. The expansion rate is negligible. Some manufacturers recommend heating it to aid in dispensing (115 to 165 degrees F). Just make sure you check the structural foam manufacturer’s
recommendations first.

Go to the vehicle maker’s Web site for the appropriate recommendations for procedures and materials. Above all, DO NOT substitute rigid, semi-rigid or pillar foam for structural foam.

• Consumer Foam — What’s consumer foam? It’s generally a one-part foam sold in aerosol cans that requires moisture to cure. It may never cure completely in an automotive application because of the dry location in the body of the vehicle. This can cause problems due to voids in the material, inadequate filling and the potential for corrosion. Not recommended! This is generally purchased at your local big box for curing drafts around doors and window jambs in your cabin. Be careful. My buddy used it around the door jamb in his garage and couldn’t get the door opened after it expanded fully.

Ordering Foam: Time It Right

As soon as you realize the vehicle you’re repairing has automotive foam in the repair area that needs replaced, order it immediately. If you have some unopened foam on hand, determine what type it is and what the shelf life was supposed to be.

It’s a sad time of life when you’re ready to add some structural foam to the pillar of a vehicle and find that you can’t get it out of the tubes because its shelf life expired a year ago. Of course, that was just after the salesman who you see once every five years came through your shop and overstocked you with a bunch of stuff that’s now obsolete. Then you call your jobber to order some new product and he tells you that it’s three days away because they don’t like to stock it due to shelf life problems.

Order it before you’re going to use it, but not before you need it. Fresh chemicals always work better.

Mixing Tip Considerations
We like to use catalyzed, two-
part seam sealers because they work. Consequently, we have a surplus of mixing tips available for when we use up the second tip that comes with seam sealer.

Question: Can I use the seam sealer mixing tip for my foam application, since I’ve used the two tips supplied with the cartridge of foam for previous applications? It fits on my tube okay, even if the length of the mixing tip is different.

Answer: Don’t do it! You’re asking for curing problems, which, considering the location of the foam, isn’t all that attractive. Imagine a wad of uncured foam inside a rocker panel, drizzling out on the customer’s garage floor. How would you clean that out of the inside of the rocker? Flush it with lacquer thinner and a flash source of ignition?

Sounds a little dicey to me. I’d rather use the right mixing tip. It’s quicker, cheaper and safer in the end.

Let me ask you this: If they make different mixing tips for different products, doesn’t it follow that to cure the material as designed by the chemical engineer who created it that you should use the exact mixing tip designed and supplied with the product?


If you use up the mixing tips for a particular product, order more and don’t listen to the local salesman when he tells you, “Don’t bother, just use your extra seam sealer tip.” Be precise and be diligent.

Application Methods
Foam application in an enclosed area requires some preplanning. No, it’s not like applying seam sealer, even though the application equipment and products may look the same. Make sure you have the proper applicator gun for the product you’re using. Many of the products use a product specific applicator gun for their specific foam. They range from simple and cheap to complicated and expensive. Make sure you have the appropriate gun for the job.

But before we start pumping foam into the pillar, we need to think about a few things:

  1. What’s the expansion rate of my foam?
  2. What’s the approximate volume I’m filling?
  3. What’s my access?
  4. Do I need a dam?

Let’s take a closer look at each …

• Expansion rate and volume to be filled — Read the label or tech sheet that’s provided with your foam. If it’s a rigid pillar foam and the expansion rate is 1 to 10, that means if you pump one ounce of foam out of your tube, you end up with 10 ounces by area of foam cured in the pillar! Calculate the volume you’re filling in advance. Determine what the plunger travel will be to dispense 1/10th of the volume you’re filling.
Get some extra mixing tips when you order the foam. Be prepared.

• Access for filling — What’s your access for filling? Good question, and the answer takes pre-planning. How far in advance do you need to plan? It depends on the access.

When you remove the part and find the foam, check for replacement access at that time. Some areas will have no access, so pre-installing the foam in your replacement part may be your only option. In that case, you’ll install the foam into the part, off the car, being careful to not overfill and to stay clear of the weld site. Attach the part after trimming off excess foam and sealing shaped areas.

Do not drill holes for access, unless recommended by the automaker.
An access hole may be much further from the end of the tip than is practical to reach. In that case, you can attach a hose to the mixing tip and achieve close proximity to the desired beginning of dispensing. In this method, it’s necessary to pull the hose toward the access hole while continuously dispensing foam. You can’t stop or the hose will become entrapped and catalyze inside the foam. Keep moving.

It’s like walking and chewing gum at the same time. Do some practice runs dry to get the feel of the process. Be completely aware of what you’re filling. Is the seatbelt carrier in the area?

If you foam it, you won’t be able to move it after!

Are there holes where the foam can drip out and
eat into the leather seats
or dash pad? Tape drip holes.

• Damming — When you took your damaged part off and found the foam, did you find plastic or metal attached to the foam but clipped to the inner part? If you did — and it’s probable that you did — that was a carrier that had a packet of heat-activated foam attached to it during the assembly process. During the bake cycle of the e-coat, the foam expanded to its engineered location. Forget it. These aren’t available to us, and we couldn’t use them even if they were because of the elevated bake temperature it takes to activate it. But keep the carrier so you can use it as a dam to prevent the foam from going where you don’t want it to go. This is important because the position of the carrier is usually the bottom end of where the foam is, and it rises from there. If your “fill” is on the vertical, you’re probably going to need a dam as the starting point of your “fill.”

If there is no carrier or it was obliterated in the collision, you’ll need to create one. There are several things you can use to create a dam, in addition to the original carriers. Balloons can be carefully blown up in position and tied off and then popped after filling. Less nerve wracking is the flexible foam packing that we all throw away. It can be tightly wadded up and shoved into a hole to expand once inside the desired location. If you’re going to install a dam and have to leave it, make sure that it’s properly corrosion protected (primed) if it’s steel.

Really, you’re only limited by your imagination, and we already know you’re creative or you wouldn’t be in this business.

Foam Smarts

To obtain thorough and complete training regarding automotive foams and their applications and uses in the collision repair industry, I recommend taking I-CAR Class FOM01 Automotive Foams. It’s an excellent course.

The proper application and replacement of automotive foams used in the modern automobile are essential to occupant safety, the structural integrity of the vehicles that use these foams, and the noise, vibration and harshness standards engineered into the vehicles by the manufacturers. It’s crucial and essential that these materials be

Writer Mike West, a contributing editor to BodyShop Business, has been a shop owner for more than 30 years and a technician for more than 40 years. His shop in Seattle, Wash., has attained the I-CAR Gold Class distinction and the ASE Blue Seal of Excellence.

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