What Causes Bubbling in Body Filler?
2 Answers
Bubbling in body filler can occur due to the following reasons: Insufficient drying of body filler: Applying paint over body filler before it has fully dried. Damaged metal panels: When performing bodywork, if the vehicle's metal panels are damaged and not properly welded before applying body filler. Improper surface preparation: Failure to completely clean the primer surface before applying topcoat paint. Poor quality body filler: Or due to excessively humid air during painting, incorrect paint mixing ratios, etc. Solutions for addressing paint bubbling: Rust prevention treatment: Remove the bubbled paint area, apply rust prevention treatment, then fill with body filler. Wait until the filler is completely dry, sand it smooth, and finally apply automotive paint. Filing a claim: If paint bubbling occurs due to paint quality issues or improper repair work, you may file a claim. It's recommended to have the issue assessed at a professional auto repair shop or 4S dealership for proper handling by specialists.
That day when I was repairing my old car, I found that the body filler had blistered, mainly because the surface wasn’t cleaned properly, and oil or moisture was trapped under the filler, causing it to expand and bubble when heated. I recalled being lazy in the past, rushing the job without waiting for the base layer to dry completely before applying the filler, especially during the high humidity of summer. The bubbles couldn’t escape, and once it dried, it blistered. When mixing the filler, patience is key to stirring it evenly in the right ratio. I was impatient and careless, resulting in too many bubbles. Applying it too thick also caused the outer layer to cure quickly while the inside remained wet. Poor-quality materials were another issue—cheap fillers with lots of impurities tend to react badly. When repairing a car, it’s best to wear gloves, clean the base layer thoroughly, and wait for dry weather before working. After the blistering, I had to sand it all off and start over, wasting time and money. It would’ve been much better to be careful from the beginning. This experience taught me that details determine success or failure—don’t cut corners when repairing a car, or you’ll face endless trouble later.