Body Filler Adhesion To E-Coat: What You Need To Know

Body filler is created by mixing polyester resin and a fill material. The choice of fill material determines the type of body filler. For instance, the original body fillers that replaced lead are filled with talc, which is a type of hard clay. However, fillers with talc are not waterproof. On the other hand, fillers with aluminium or fibreglass as the fill material are moisture-resistant.

Body filler should be applied in thin layers, ranging from 1/8 inch to 1/4 inch thick, with dry time between layers. It is designed to be used in temperatures ranging from 60 to 90 degrees Fahrenheit.

Regarding the application of body filler over e-coat, there are varying opinions. Some sources claim that body filler should not be applied over sanded paint, as it can cause repair mapping, which is often mistaken for sand scratch swelling or primer shrinking. However, others argue that applying body filler over sanded paint is acceptable, especially if it is an OEM substrate, which refers to a factory paint job that has never been repainted.

It is important to note that adhesion problems may occur if the surface is not properly prepared and cleaned before applying the body filler.

Body filler and epoxy primer

The traditional method of applying body filler is to grind or sand the damaged area down to bare metal and then apply the filler. This ensures good adhesion and prevents corrosion. However, some technicians have started applying body filler over sanded paint, as it is much quicker and does not disturb the factory zinc coatings and e-coat, which provide superior corrosion protection.

There is some controversy over whether body filler can be applied over sanded paint. Some people argue that it can cause repair mapping, where the chemicals in the filler react with the layers of paint, causing them to swell or shrink. Others claim that it works fine as long as the paint surface is an OEM finish and the filler is applied correctly.

One way to address the controversy is to use an epoxy primer as a base coat over the bare metal or blasted car before applying body filler. This provides extra corrosion protection and is often done for restoration work or when the car will not be completed for some time. However, for collision repair that is filled the same day, this may seem like an unnecessary step.

When applying body filler, it is important to follow the manufacturer's instructions and use the correct amount of hardener. The filler should be applied in thin layers, with dry time between layers, to ensure proper curing and adhesion.

Overall, there are pros and cons to using body filler over epoxy primer or bare metal. It is essential to consider the specific circumstances and make an informed decision based on the available facts and opinions.

Body filler and bare metal

Body filler can be applied to bare metal, but it is not always the best option. When filler is applied to bare metal, there is a risk of rust forming under the filler over time. This is because body filler absorbs moisture, which can then reach the metal underneath.

To avoid this, some people choose to apply a base coat of epoxy primer before applying the filler. This seals and protects the bare metal from rust. Epoxy primer can also be applied after the filler has been sanded, to further protect the metal from corrosion. However, this is not necessary if the filler is applied to bare metal and the car is going to be painted soon after.

If you are performing warranty work, you should consult the manufacturer's recommended procedure. Some auto manufacturers require body technicians to coat the bare metal surface with an epoxy primer before applying fillers.

When applying body filler, it is important to follow the manufacturer's instructions for mixing and application. The filler should be applied in thin layers, with dry time between layers. The area to be filled should be sanded and cleaned to ensure good adhesion.

Body filler and powder coating

Body filler is a substance used to repair dents, creases, and imperfections in metal surfaces, such as car bodies. It is created by mixing polyester resin and a fill material, with the specific type of filler depending on what the fill material is made from.

Powder coating is a painting process in which a paint powder is applied to a metal surface electrostatically and then cured in an oven at temperatures that can exceed 400°F (204°C).

When it comes to using body filler for surfaces that will be powder-coated, there are some important considerations. Firstly, regular automotive body fillers are not suitable for use under powder coating. These two-part fillers tend to shrink, pop out, burn, outgas, or leave visible rings through the powder coating. The powder typically does not adhere well to the surface of these fillers, resulting in visible damage and costly rejections.

Instead, a metal repair filler designed specifically for use under powder coating should be used. Examples of such fillers include Lab-Metal, Hi-Temp Lab-Metal, EPO Strong, Evercoat Metal 2 Metal, and All Metal. These fillers are able to withstand the high temperatures of the powder coating process and provide a suitable surface for the powder to adhere to.

It is important to follow the manufacturer's instructions when using these fillers and to consider factors such as the temperature and duration of the curing process. Additionally, proper surface preparation is crucial for good adhesion of the body filler. The surface should be clean and free of any wax, grease, or other contaminants.

By using a suitable metal repair filler and following the necessary preparation and application steps, body filler can be successfully applied to surfaces that will be powder-coated, resulting in a strong and durable finish.

Body filler and adhesion

The adhesion of body filler is dependent on good surface preparation. If the area is not clean and free of wax, grease, or other contaminants, the filler won't stick. It is important to remove all coatings several inches past the repair area to ensure that body filler is not applied over paint. Sanding the repair area with 24-, 36-, or 80-grit sandpaper is also crucial for creating a rough surface that allows the filler to grip and bond to the vehicle.

Standard-grade body filler is lightweight, easy to spread, and dries in around 20-25 minutes. While it sands down easily to blend seamlessly with the rest of a vehicle's surface, it doesn't offer stain resistance, and colour from the filler can stain the surface. It is also not recommended for use on galvanised steel.

Medium-grade body fillers are typically fibreglass-filled and offer better stain resistance than standard fillers. They adhere well to a variety of body surfaces like metal and fibreglass and are ideal for repairing small holes or cracks. However, the reinforced nature of this filler can make it more difficult to work with and requires some practice to get used to the more rigid formula.

Premium-grade body filler is made from top-quality resin with the highest stain resistance and is the easiest to sand down, offering the best adhesion. It is ideal for repairing larger areas of a vehicle but is also the most expensive option.

Before applying body filler, it is crucial to adequately prepare the vehicle's surface. This includes cleaning the area with warm water and a clean microfibre cloth, applying a good-quality primer, roughing up the surface using coarse sandpaper, and using a degreaser to ensure a clean, oil-free surface.

When mixing body filler, it is important to use a non-porous surface such as metal or plastic. The filler and hardener should be mixed in the exact proportions stated on the packaging to avoid problems with curing. Insufficient hardener can result in the filler not completely curing, while too much hardener can cause excessive heat during curing, more pinholes, and lower cured strength.

During application, the body filler should be pressed firmly and fully into the surface to prevent air pockets that will reduce adhesion and strength. It is also important to frequently wipe the edge of the applicator to remove any filler that has started to dry, as this will leave tramlines in the surface.

After the filler has fully cured, use a sanding block with coarse-grit paper to gently remove any protruding filler, sanding it back to the finished level. This process may need to be repeated with additional coats of filler to achieve the desired finish.

Body filler and corrosion protection

Corrosion protection is crucial for maintaining the appearance and structural integrity of a vehicle. It is essential to use up-to-date products and procedures to prevent rust and corrosion on the vehicle's surface and beneath it.

Body Filler Application

When applying body filler, it is important to follow the manufacturer's instructions for preparation, filling, and finishing. The surface should be thoroughly cleaned, removing any rust, dirt, or loose paint, and sanded to create a rough surface for better adhesion. Body filler should be applied in thin layers, gradually building up to the desired thickness, and feathered to blend seamlessly with the surrounding area.

Types of Body Fillers

There are several types of body fillers available, each designed for specific applications:

• Polyester fillers (Bondo) are versatile and suitable for repairing metal, fiberglass, and wood surfaces.
• Epoxy fillers are durable and have excellent adhesion properties, making them ideal for repairs in areas with high moisture levels, such as the undercarriage.
• Lightweight putties are similar to polyester fillers but are easier to sand and shape.
• Plastic body fillers are designed for surfaces like bumpers, mirrors, and trim where normal fillers won't adhere properly.

Corrosion Protection Techniques

To restore corrosion protection to a vehicle, several techniques and products can be used:

• Weld-through primer: Coats bare steel with zinc to protect against corrosion.
• Sealers: Fill gaps and seal seams to protect vulnerable areas from air, moisture, and road noise.
• Rust proofing materials (cavity wax): Waxy compounds that seal cracks and crevices in interior closed surfaces.
• Undercoatings: Compounds applied to exposed exterior surfaces to protect sheet metal from flying stones and other debris.
• Corrosion protection primers: Applied directly to bare and uncoated steels, such as self-etch primers and two-component epoxy primers.

Best Practices

To achieve the best results and ensure proper corrosion protection:

• Always follow the vehicle manufacturer's repair manual and recommendations.
• Consult with paint system manufacturers to ensure compatibility with weld-through primers.
• Use corrosion protection primers as a base before applying body filler.
• Featheredge the surrounding area of the repair to ensure a smooth transition.
• Apply a high-quality automotive primer after using body filler and before painting to enhance adhesion and provide additional protection.
• When painting, match the paint colour precisely and apply thin, even coats, allowing each coat to dry completely.

Frequently asked questions