Body Fillers

Body filler is an essential product for repairing dents, scratches, rust damage, and panel imperfections before painting. Whether you are restoring a classic vehicle, repairing minor car park damage, or preparing panels for a respray, using the correct automotive body filler ensures a smooth and durable result. Repco’s range of body filler products includes solutions for metal, plastic, and fibreglass surfaces, allowing you to match the filler to the repair.

From standard car body filler and lightweight finishing car putty through to reinforced fibreglass filler and plastic bumper filler, Repco’s range supports both minor cosmetic touch-ups and more involved structural repairs. Choosing the correct auto filler for your specific repair improves adhesion, flexibility, and long-term durability.

What is body filler and what are some variants of this?

Body filler, often referred to as car bog, automotive bog, or bog filler, is a polyester-based compound used to fill and level damaged areas on vehicle panels. It is typically supplied as a two-part system consisting of a filler base and a cream hardener. When mixed, the compound chemically cures into a sandable, rigid material.

There are several common variants available in Repco’s range:

• Standard automotive body filler for general dent and surface repairs on steel panels
• Metal filler or metal body filler formulated for strong adhesion to bare steel or aluminium
• Fibreglass filler, also known as fibreglass bog or fibreglass body filler, reinforced with glass strands for added strength
• Plastic filler or plastic body filler designed for flexible components such as bumpers
• Lightweight finishing filler or car putty for minor imperfections and final surface levelling

Fiberglass body filler variants are particularly useful where extra structural support is required, such as repairing rust holes after metal patching. Plastic bumper filler is formulated to accommodate movement in modern bumper bars without cracking. Selecting the correct car filler ensures the repair remains stable under vibration and temperature changes.

How to use body filler to repair dents

Effective dent repair begins with surface preparation. Sand the damaged area back to bare metal where necessary, removing paint, rust, and contaminants. Use 80-grit abrasive paper to create a keyed surface that promotes adhesion. Clean the area thoroughly with wax and grease remover, ensuring it is dry before application.

Mix the body filler with the supplied hardener according to manufacturer ratios, typically around 2 to 3 percent hardener by volume. Over-hardening can cause premature curing and brittleness, while under-hardening can prevent full cure. Only mix what you can apply within the working time, usually 3 to 5 minutes depending on temperature.

Using a body filler applicator or spreader, apply the automotive filler in thin, even layers. Avoid applying excessively thick coats, as this can trap air and create weak spots. Allow each layer to cure fully before sanding. Initial shaping can be done with 80-grit paper, followed by 120-grit and finishing with 240-grit to refine the surface.

For deeper repairs or areas where metal has been welded, a fibreglass filler or metal bog may be applied first to provide strength. A finer auto body filler or car putty can then be used to achieve a smooth finish before primer application. Repco’s range of automotive body filler products supports this layered approach to ensure strong and accurate repairs.

Why do I need to use the right body filler?

Using the correct filler is critical for adhesion, flexibility, and durability. Steel panels require a metal body filler that bonds securely to bare metal and withstands panel vibration. Aluminium panels may require specific metal filler formulations to ensure proper bonding.

Plastic components such as bumper bars expand and flex with temperature changes and minor impacts. Using standard car bog on these areas can result in cracking. A plastic bumper filler or plastic body filler is formulated to retain flexibility after curing, making it suitable for bumper repair kit applications.

Fibreglass filler or fibreglass body filler is appropriate when repairing fibreglass panels or reinforcing rust repairs. The embedded glass strands provide added strength, helping bridge small gaps and restore panel integrity.

Repco’s range of body filler options allows you to select the right automotive filler for each stage of the repair. Matching the product to the panel material ensures the repair remains stable over time and reduces the risk of shrinkage, cracking, or paint failure.

Tips for effective body filler usage

Preparation determines the quality of the result. Always remove rust completely before applying bog filler. If rust remains, it will continue to spread beneath the repair. Use clean mixing boards and tools to prevent contamination.

Apply filler in controlled layers rather than one heavy application. Keep the spreader at a consistent angle to minimise air pockets. Sand in a cross-hatch pattern to maintain panel shape and avoid low spots.

Temperature affects curing time. Warmer conditions accelerate curing, while cooler conditions slow it down. Store automotive bog and hardener in a cool, dry environment. Always wear gloves, eye protection, and a suitable respirator when sanding.

Repco’s range of auto filler products includes options for both small touch-up jobs and larger panel restorations, giving you flexibility whether you are repairing a single dent or completing a full respray preparation.

What is body filler made of?

Most body filler products are made from polyester resin combined with talc or similar mineral fillers. The cream hardener contains benzoyl peroxide, which initiates the curing reaction when mixed. Once cured, the material forms a rigid yet sandable surface that adheres strongly to prepared substrates.

Fibreglass filler includes chopped glass fibres within the resin matrix to provide structural reinforcement. Plastic body filler formulations include additives that maintain flexibility after curing, making them suitable for bumper and trim repairs.

This composition allows automotive body filler to bond securely to steel, aluminium, fibreglass, and certain plastics when properly prepared. Repco’s range of body filler products is compatible with automotive primers and topcoats, allowing you to complete repairs with professional results.

To complete your repair properly, consider pairing your body filler with automotive primers, sanding and surface preparation tools, and touch-up or spray paint products from Repco’s range to ensure a consistent and durable finish across the entire panel.