What can happen if filler is applied too thick?

• A. It may crack or fail
• B. It improves durability
• C. It dries faster
• D. It hides rust

Answer: (A)

Filler is meant to be applied in thin coats so it cures evenly, adheres well, and can be shaped with simple sanding. If it’s applied too thick, the outer layer can harden while the inner portion is still curing, creating internal stress that leads to cracking, crazing, or eventual failure of the repair. Thick applications also don’t cure uniformly and can delaminate from the substrate or chip off with vibration. This option doesn’t make the repair stronger or faster to dry; it actually reduces durability and can trap moisture or air pockets. And filler isn’t a rust solution—rust must be treated separately, since filler won’t stop corrosion.