What Causes Bubbling in Body Filler?

[KimberlyMarie]

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.

[DiWyatt]

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.

[LeAriana]

I've been in this line of work for years, and there are only a few common causes for filler blistering. First is inadequate cleaning—dust and grease left on the car body will cause bubbles when the filler is applied. Second is incorrect mixing ratio—too much or too little hardener affects curing, making it prone to air bubbles. Third is environmental factors—high humidity during rainy seasons lets moisture seep into the filler layer and expand, or uneven high-temperature baking. Skillful application is key—thin coats, multiple layers, and careful sanding. I’ve seen beginners apply it too thick, causing the outer layer to harden while the inner stays soft, leading to blistering. Don’t skimp on material quality either—cheap fillers contain impurities and degrade easily. Prevention is simple: clean the surface with degreaser, work in low-humidity conditions, and mix the filler thoroughly. Though a small issue, it’s frustrating—just sand it down and reapply fresh filler promptly.

[AllisonMarie]

Bubbling in body filler often occurs when the substrate is dirty, trapping oil or moisture that expands. Incorrect mixing ratios or uneven stirring can cause bubbles, and applying too thickly leads to fast outer curing but slow inner drying. Humid weather or large temperature changes also contribute. From personal experience, clean the surface thoroughly and let it dry before applying filler, using a small fan to remove bubbles and prevent blistering. Choose high-quality filler to avoid impurity issues.

[SanLayla]

I often encounter issues with body filler blistering during car repairs, mostly due to neglected cleaning: oil stains or water droplets get covered by filler before drying, causing bubbles when heated. Mixing errors like stirring too fast trap air bubbles, while incorrect ratios lead to uneven curing. Uneven application worsens the problem. High humidity or poor-quality materials exacerbate it. For prevention, always clean and dry the base layer thoroughly, mix filler evenly, apply in thin multiple coats, and choose sunny days for work. When fixing, sand carefully to avoid damaging the original paint. After learning the hard way, I've developed a habit: being meticulous with every repair to avoid rework and save time and effort.