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How They Work: Filler

There’s an old adage: “You get what you pay for.” With body fillers, this is certainly the case. I’ve always recommended that owners and managers focus on the total cost of each process versus looking at consumables, labor and overhead costs individually.

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Karl Kirschenman is the president for K2 Consulting Group and holds a Bachelor of Science degree in communication, with over 10 years of experience in the collision industry. He has previously worked as the collision program manager for ALLDATA and the director of technology for I-CAR.

Proper panel prep can resolve many of the issues surrounding body filler application.

Proper panel prep can resolve many of the issues surrounding body filler application.

This month, we’re going to focus on body fillers. Because September is a month where temperatures and humidity fluctuate widely, it only makes sense that we talk about this miracle of resin technology in this issue.

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Picking the Correct Body Filler

There’s an old adage: “You get what you pay for.” With body fillers, this is certainly the case. I’ve always recommended that owners and managers focus on the total cost of each process versus looking at consumables, labor and overhead costs individually.

Most manufacturers have a product line that includes a good, better and best option. While it’s easy to see that the best product option is more expensive for the actual product itself, what you may be missing is the cost to use that product in terms of reduced consumables and reduced labor time. Of course, we know that reduction in labor hours can go a long way toward improvement in your cycle times.

If you haven’t looked into new body fillers in the last few years, it may be time to ask for a demo on the latest products from your preferred manufacturer. Ask them to perform an in-shop demo for the techs and your shop personnel. See if there are savings to be had with newer products or higher quality products. Look for costs throughout their proposed process and check to see if the new product allows for easier sandability within the process. Also, look at reduction in putty usage, glazes and sandpaper that can offset the additional costs of premium body filler and materials.

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It’s All About 2%

Many of us mix the body filler and hardener differently as the seasons change, and we use filler with increased or decreased amounts of hardener as weather conditions change. The problem is you may not be catalyzing the body filler properly as you make these adjustments. Most technicians mix the body filler by color instead of using a scale. This is a perfect recipe for comebacks. You can get close on color, and many techs do every day. You probably get away with it most of the time. However, you cannot get a perfect catalyzation using color alone to gauge hardener ratio, no matter how good you are.

During my discussions with several industry professionals for this article, the No. 1 item each person stated was a concern is the correct usage and implementation of hardeners. Both under- and over-catalyzing of hardeners have their own side effects.

You want to have the correct amount of hardener in your body filler. By using a scale to mix your product, you can guarantee an accurate mixture to 2 percent catalyzation every time. Consistency and repeatable processes are what you need to strive for within every operation in your facility.

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There are manufacturers out there that have body fillers that react differently to hardeners, depending on the temperature. So, let’s say you’re working in the winter and have the ability to use a filler that’s designed for cooler temperatures and the same goes for warmer temperatures. You’re still going to mix the catalyst at that magic 2 percent, but you’ll have more time to work the product depending on the body filler type being used. Again, the key here is the proper amount of catalyst in your body filler.

While we’re talking about hardeners, let’s not forget that they break down over time and separate. If you notice you have a hardener that has a high amount of liquidity or is separated, dispose of it and get another tube.

Another common issue is the inter-mixing of hardeners from different manufacturers. A 3M hardener goes with 3M body filler. The same goes for every other manufacturer. If your jobber is not delivering the correct manufacturer’s hardener with your body filler, you need to have a pointed conversation with them.

Each manufacturer designs their hardeners to chemically react to their body filler for optimal results. No manufacturer is going to stand behind their body filler if you used competitor’s hardener to catalyze the product.

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Prepping the Panel

A lot of issues surrounding body filler application can be resolved during the panel prep stage. How many of you have pulled a car into the booth, used some air to spray it off and began sanding on a panel? It happens all the time. Now the real question is, are you removing all of the contaminants just using some air and your hand to rub the surface? Of course not.

To properly begin the panel prep process, start off with using soap and water to wash the vehicle. Follow the car wash with a wax and grease remover application to the repair area. It’s critical that you perform these procedures in order to prevent contaminants from being pushed into the surfaces you’re working on. You need to do these steps before any sanding of the vehicle takes place. If you say to me that you’re not getting paid to wash cars, let me ask, how much are you getting paid for comebacks?

Mixing the Product

After your panel is prepped, measure out and mix the body filler and hardener. Locate a nice, clean surface to mix your product. Several manufacturers have low-cost products that allow mixing of filler and use during the application process. It is not recommended to use plastic, metal and glass surfaces to mix your product. It’s easy for contaminants to be lodged in the surfaces of these materials. Cleaning and reusing these surfaces is also not recommended as the cost of solvents and labor time outweighs the consumable costs for temporary mixing surfaces.

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Using cardboard for mixing your body filler is never recommended for a number of reasons. Cardboard is a porous surface that will allow the resin to soak in. In addition, cardboard surfaces contain debris such as dirt, sand, dust, ink, loose cardboard particles, etc. Any of these items can ruin a great repair and cause the car to come back in six months or more. Why take the chance using leftover cardboard to save $1 in consumables? I recommend using some disposable paper sheets designed for the mixing and application of body filler. You’ll be surprised just how quickly the cost of cleaning reusable surfaces comes down and labor time is reduced.

When physically mixing the materials, look for a nice, uniform product color during the mixing process. It’s recommended that you fold the product and not whip the product like a cake. Whipping (swirling with a screwdriver for instance) adds air to the product. Unnecessary air can introduce pinholes and adhesion issues during the application and curing processes.

Upon having a nice, uniform mix of the product, spread it out into a thin layer on your disposable mixing surface. The more concentrated the materials are on your disposable mixing surfaces, the faster the materials will cure. Our goal is to get the most time available with the product before it sets up, so a thin layer is the ticket to getting you the most time possible. Typically, that’s only three to six minutes, so every second counts.

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Applying the Product

With changing temperatures and humidity levels, body filler needs to be worked differently. When I say “worked,” I’m not talking about adding or reducing the amount of hardener that’s used. I’m talking about the amount of time that a technician has to use the product before needing to apply another layer.

In summer, you may need to apply smaller coats – depending on your manufacturer – than you do in winter. The product is going to set up faster, and you want to make sure you have maximum adhesion of the product to the panel. Rule of thumb is if you can’t cover the area within the three- to six-minute time window, use multiple coats to complete the repair process. Depending on the manufacturer, consider sanding each layer before applying additional filler. This promotes adhesion between the layers.

Spread thin layers of body filler onto your panel, removing any spreader trails as these can trap air into the panel surface. The maximum recommended thickness for body filler is .25”. If you feel the need to go thicker than .25”, you should really look into using a glass-reinforced filler before the application of body filler.

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Again, sand between each application layer of filler. After completing your layers, allow drying time, sand and finish as necessary. For those who like to shape-sand during drying stage, be sure to check out newer body filler products that present increases in sandability after the drying has been completed. Finally, be sure to check for any signs of repair mapping before sending to paint for refinishing.


Contributors to this article include Carl Seaboldt – senior product manager, Evercoat;  Ricky L. Miller – senior technical service engineer, 3M Automotive Aftermarket Division; Brian K. Lewis – technical services manager, U.S. Chemical; and Gary Holt, Clean Sheets.

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