Bondo Body Filler
Our original automotive bondo formula has been the trusted choice of professionals and DIY enthusiasts since 1955. This two-part epoxy filler repairs dents, rust damage, holes, and surface imperfections on metal, fiberglass, and wood surfaces.
The smooth, creamy consistency spreads easily and sands to a feather-edge finish. Our automotive body filler cures in 15-20 minutes and provides a rock-solid foundation for primer and paint. Each quart includes a tube of hardener cream for precise mixing and application.
Automotive body filler specifications
Materials & Formula Composition
Bondo automotive body filler uses a two-part polyester resin system engineered for maximum adhesion and durability. The base compound contains micro-fine talc particles suspended in polyester resin, creating a smooth, non-sagging consistency that holds vertical surfaces without slumping.
The included red cream hardener contains methyl ethyl ketone peroxide (MEKP), which catalyzes the curing reaction when mixed with the base filler. We recommend a 2% hardener ratio by volume—approximately a golf-ball-sized dollop of filler to a 1-inch ribbon of hardener. Our formula bonds directly to bare metal, E-coat primer, fiberglass gel coat, and properly prepared wood surfaces.
Application & Surface Preparation
Cleaning & Sanding
Proper surface preparation determines repair longevity. Grind or sand the damaged area to bare metal using 36- to 80-grit abrasive. Remove all paint, primer, rust, and loose material at least 1 inch beyond the visible damage. Feather the paint edges to create a gradual transition.
Clean the sanded surface with wax and grease remover. The metal must be completely dry before applying automotive bondo. Any moisture, oil, or contamination will prevent proper adhesion.
Sanding & Finishing Techniques
Begin sanding when the filler reaches a firm, cheese-like consistency—typically 10-15 minutes after application at room temperature. Use 36- or 40-grit sandpaper for initial shaping while the material is still slightly soft. This “cheese-grater” technique removes excess material quickly and prevents loading your sandpaper.
Once fully cured (30 minutes minimum), switch to 80-grit for general shaping, then 120-grit for smoothing, and finish with 180- or 220-grit for final surface prep. Sand in crossing patterns to maintain a flat, even surface. Our automotive bondo sands to a true feather edge at the repair perimeter, creating an invisible transition to the original panel.
Complete Your Auto Body Repair Kit
Rated 4.8 by verified buyers
Questions About Bondo Body Filler
Mix approximately 2% hardener by volume—about a 1-inch ribbon of red cream hardener per golf-ball-sized amount of filler. The mixture should turn uniform pink when properly combined.
Using too much hardener (over 3%) causes the cured filler to become brittle and prone to cracking. Too little hardener (under 1.5%) extends cure time excessively and may result in soft, under-cured material that won't sand properly. Temperature affects cure time, so adjust your working pace accordingly in hot or cold conditions.
No, you must remove all rust, paint, primer, and loose material down to bare substrate before applying body filler. Sand or grind the area with 36- to 80-grit abrasive, extending at least 1 inch beyond the damage.
Bondo automotive body filler bonds through mechanical adhesion—it grips the microscopic texture created by sanding. Rust, paint, and contamination prevent this bond, leading to eventual delamination. For rusted areas, treat bare metal with an epoxy primer or rust converter before applying filler to prevent future corrosion from underneath.
Apply automotive bondo no thicker than 1/4 inch per layer for optimal curing and adhesion. Thicker applications trap solvents and may cure incompletely in the center, resulting in shrinkage or cracking weeks after painting.
For repairs deeper than 1/4 inch, build thickness gradually in multiple layers. Allow each layer to fully cure (30 minutes minimum) before applying the next. For very deep damage exceeding 1/2 inch, use fiberglass resin and cloth for the base layers, then finish with body filler for the final 1/4 inch.
Bondo body filler becomes sandable in 15-30 minutes at 75°F, depending on hardener ratio and ambient temperature. You can begin initial shaping with coarse sandpaper (36-40 grit) when the surface reaches a firm, cheese-like consistency—usually 10-15 minutes after application.
Cold temperatures below 60°F significantly extend cure time. In temperatures above 85°F, working time decreases to 3-5 minutes, so mix smaller batches. For final sanding and primer application, wait at least 30 minutes to ensure complete cure. The filler should be rock-hard with no soft spots.
Standard Bondo automotive body filler is not recommended for flexible plastic bumpers made from TPO, polyurethane, or polypropylene. The rigid cured filler will crack when the flexible bumper flexes during normal use.
For plastic bumper repairs, use Bondo Flexible Filler, which is specifically formulated to remain slightly pliable after curing. It bonds to plastic substrates and moves with the bumper material. For semi-rigid plastics like fiberglass or SMC (sheet molded compound), our standard body filler works perfectly.
No, you must apply automotive primer over cured and sanded body filler before painting. Bondo is porous and will absorb paint solvents, causing poor paint adhesion, discoloration, and eventual failure.
After sanding the filler smooth with 180- or 220-grit sandpaper, clean the surface thoroughly and apply two coats of automotive primer. Epoxy primers provide the best adhesion and corrosion protection. Once primed, you can apply any automotive paint system—single-stage, basecoat-clearcoat, or custom finishes.
Seal the container tightly after each use and store in a cool, dry location between 60-80°F. Avoid heat sources, direct sunlight, and freezing temperatures.
Once opened, use the product within 12 months for best performance. If a watery layer develops on top or the filler shows separation, discard and replace. Never pour unused mixed filler back into the container—the hardener will contaminate the entire batch. Store the cream hardener tube with the cap tightly sealed; replace if it becomes thick or discolored.