Work in the business world long enough and you'll discover that oftentimes a less than stellar reputation is not deserved. The automotive industry is rife with examples.
Consider the dim view American consumers held for years for Fiat products. Ridiculed for decades as substandard, poorly engineered import mistakes, Fiats in reality were solid little vehicles. Their bad reputation, according to fans of the Italian compacts, was mainly the product of an embarrassingly weak dealer network that offered little support. Making a bad situation worse, new owners frequently created additional problems by putting their own questionable mechanical skills to work on these vehicles or by turning them over to technicians who guessed their way through repairs because they didn't have time to run down the OEM instructions.
In collision repair, body fillers sometimes have been stuck with similar undeserved criticism. Mention fillers to customers and you're likely to set off negative perceptions borne from witnessing the worst of filler repairs--namely, jobs performed by DIYers who misuse these products or fly-by-night used vehicle lots that overuse/misuse fillers to disguise deeply flawed cars requiring more professional work.
The truth is body fillers are vital, central parts of collision repair that manufactures have significantly improved over the past several decades. When given the attention they require, they can perform flawlessly.
Refer to the following application steps, recommendations and tips to get the most from the latest fillers.
Application basics
Sticking to the instructions from each filler manufacturer is vital. The following steps, supplied by 3M (the manufacturer of Bondo), provide the basic instructions for most filler applications.
Step 1. Clean the area. Begin by using hot soap and water to clean the filler area. Then, use a residue remover to eliminate any remaining wax, grease, tar or other residue. Remover is especially important here since road and other debris can "contaminate" the filler and hinder its adhesion.
Step 2. Sand the area. Using 80 grit paper on either a block or orbital sander, remove all paint in a 2 in. area surrounding the area to be filled. When finished, be sure to remove any grit debris from the area using the residue remover.
Step 3. Mixing and application. Because filler begins hardening as soon as it's mixed with hardener, dispense only an amount that can be applied within three minutes (normally a pool with a 4 in. diameter). Make sure the mixing surface is clean and nonporous. Spread the initial layer of mixed filler over repair area, applying firm pressure to ensure maximum adhesion. Add additional layers to build the repair. Avoid over application since you'll sand off any excess. Allow the filler to dry for 15 to 20 minutes, depending on humidity and temperature, before sanding.
Step 5. Shape the repair. Using a sanding block suitable for the size of the repair, attach an 80 grit sheet and begin shaping the repair area. Make sure to keep the block flat to the surface, and do not over sand. Examine the repair area, looking for any low spots that will need filler applied. If necessary, apply the additional filler and repeat the sanding/examination process.
When complete, fit a 180 grit abrasive sheet to the sanding block and level off the area and remove any remaining 80 grit scratches.
Step 7. Featheredge. Using the same 180 grit abrasive sheet, featheredge the paint away from the body filler. Remove any straight line scratches.
Step 8. Final cleaning. Remove any remaining sanding debris. 3M also recommends using glazing and spot putty to fill any pinholes or minor imperfections.
Professional recommendations
Basically, most filler jobs involve prep, mixing the filler and hardener, application and sanding. As simple as that may be, there's plenty of room for mistakes if shops don't attend to other rules and recommendations during this process.
Fresh product. When properly sealed and stored, filler remains usable for some time. Hardener, on the other hand, can begin "breaking down" and losing its effectively even before it's opened. Always check the manufacturer recommendations on both with a special eye on hardening products.
Mixing the filler. Resin can begin separating from filler in both used and unopened containers. Before using, use a paint stick to stir the filler and blend the resin back into the compound. Never shake the container to blend the filler. According to US Chemical and Plastics Product Manager Bob Olszak doing so (especially with a can shaker) creates pin holes in the filler that will need repaired.
Catalyst ratio. Pinholes also can result when filler and hardener aren't mixed correctly. Brian Lewis, a technical manager for US Chemical and Plastics, says the most common mistakes he helps customers address deal with mix ratios. Ideally, the ratio of filler to hardener for most products is 50:1. Lewis notes that using too much hardener produces pin holes and bleaching of the paint. Use too little, he says, and the result is staining and de-lamination of the paint.
Typically, shops measure out hardener by forming the filler into a circle (4 in. in diameter) and squeezing out a bead of hardener from one edge of the circle to the opposite side. Because there is some guesswork here, Lewis says his company has responded by creating hardener tubes with openings designed to consistently deliver an accurate amount.
After the hardener has been placed on the filler, the two must be mixed by continually folding and pressing them together until the color of the filler has changed throughout. Never "stir" the filler and hardener together since this creates air pockets that later produce pin holes.
Layered effect. Filler always must be applied in multiple layers, with firm pressure placed on the foundation layer to push out any air pockets. Ricky Miller, Senior Technical Service Engineer, 3M Automotive Aftermarket Division, notes that one of the biggest mistakes shops make is creating a primary layer that is too thick since forcing air out a thick layer can be particularly difficult. Any air that remains could blister and damage the repair.
Miller also notes that repairers need to smooth out spreader trails between layers. As the technician completes each layer, a small edge is produced by the smoothing action of the spreader. This edge needs to be rolled over to push out any remaining air (that, once again, creates pin holes).
Depth dimensions. As tough as filler is once it hardens, repairer must never exceed the recommended usage. Repairable dents can be no deeper than 1/4 in. Putty can be applied to scratches no deeper than 1/8 in. Exceeding these limits means risking the integrity of the filler, which can begin to crack over time.
Proper temperature. Extremes in temperature and humidity can affect hardening times in fillers, making application difficult. In warmer climates where the filler can begin hardening quicker than normal, technicians compensate by cutting back on hardener to slow the process. In colder areas, techs add a bit more hardener speed up a process slowed by cooler temperatures. With a little experience, determining the revised ratio of hardener to adjust the filler's working time should be no problem (also contact the manufacturer's tech line for recommendations).
(photo courtesy of 3M) Use 180 grit sandpaper to level off the repair area and remove any of the 80 grit scratches.
Lewis points to a low temperature problem some small shops experience when they choose to perform filler work at the end of the day, with the intent of letting the filler dry overnight to be painted the next morning. In normal shop working temperatures (around 70 degrees F) this practice would be fine. If night time temperatures dip below 55 degrees F and shop turns down its heat, the filler will stop drying. In the morning, the shop will have to continue to wait for the filler to dry to be painted.
High humidity is a much larger factor since it has the potential to greatly extend curing times. In some cases (such as the high humidity areas of South Florida), the filler won't dry properly on its own, and the job will need to be re-done. Olszak recommends shops located in these climates use a heat lamp on the filler after it has been applied.
Paint prep. Before any filler is painted, Miller says shops need to examine the work one more time to find flaws. Because the lighting in some shops is poor, Miller recommends techs or paint prep workers blow off any remaining grit and use a small flashlight to look for pin holes or grit scratches. Aim the flashlight at the side of the repair, not directly on it, for best results.
New products. Many of the challenges shops have traditionally faced using fillers have been addressed by new products designed to make this work easier and even more practical. Miller says 3M's Dynamic Mixing Systems now include products designed for use in hot and cold temperatures. For example, 3M's Dent Filling Compound - 95 provides 3.5 minutes working time when used at 95 degrees F. The cool weather version can be used in temperatures as low as 55 degrees F, with the product being ready for sanding after 15 minutes.
Lewis says shops interested in powder coating can turn to US Chemical and Plastics' All-Metal filler. Fillers typically can't be powder coated since they don't work properly with the 400-450 degree F heat required (the substrate cools before filler and pulls away, creating a gap). All-Metal filler can and therefore gives the collision market, especially specialty and restoration shops, an important product option.
Of course, both of these fillers and many similar products making their way to the market must be used correctly. When they are, they can help your business build the kind of great reputation they too deserve.
