Why must body filler be mixed properly?

• A. To ensure proper curing and strength
• B. To accelerate painting
• C. To reduce weight
• D. To change color

Answer: (A)

Body filler is a two-part polyester system that cures through a chemical reaction between resin and hardener. The mix ratio controls how completely that reaction occurs. When mixed properly, the filler hardens to its intended strength and stiffness, providing a stable, sandable surface that will hold up to primer and paint. If the mix is off, the cure may be incomplete or uneven: too little hardener leaves a soft, gummy filler that can crack, lift from the metal, or absorb moisture; too much hardener can create excess heat, leading to shrinkage, cracking, or an overly brittle surface. Either scenario makes sanding and finishing unreliable and can compromise the repair’s durability. Following the manufacturer’s recommended mix ensures proper curing and strength.