Can You Use Bondo On 3D Prints? Guide To Fixing Print Gaps!

Finishing can take a print from amateur to professional. Removing flaws, filling in gaps, painting and smoothing out rough edges can elevate your work and literally make it shine. 

Filling in gaps is one of several steps in post-processing a print. Though used primarily for repairing auto body panels, Bondo spot and glazing putty can also be used to fill gaps in 3D prints. One characteristic that makes Bondo popular is its ease of use. Unlike other fillers, Bondo is not a two-compound filler that requires mixing before use. 

Bondo is quick-drying, becoming ready for sanding in 30 minutes. It is also non-staining which means it will not alter the color of your prints. It sands well which allows you to get a smooth shiny finish on your prints. 

The biggest downside to it is its toxic odor. You want to be in a well-ventilated area when working with it. You should also use gloves and a dust mask while you’re working as Bondo has been known to cause headaches from prolonged exposure.

On a side note! If you’re looking for a reliable and high-quality 3D printer, we highly recommend the Official Creality Ender 3 V2 Upgraded 3D Printer (Amazon Link).

This printer is an upgraded version of the popular Ender 3 model, with a range of new features and improvements that make it even easier and more convenient to use.

The Ender 3 V2 is an excellent choice for beginners, kids, and experienced users.


There is, however, more than one way to finish a print and Bondo is not the only filler. There are several other alternatives as well as methods that do not require filler at all. What are they? Read on to find out.

How Do You Fix The Gaps On My 3D Prints? Printer/Slicer Settings

Gaps in prints can be prevented by adjusting printer or slicer settings before printing. This includes adjusting the layer height, fill density, print speed, print temperature, filament quality and shell thickness. Filler can be used to fix gaps that remain after printing.

The simplest way to fix gaps is to minimize their occurrence. In this way you spend less time fixing them in post-processing. Your slicer settings are your biggest ally in reducing gaps in your prints.

There are the main settings you should look to adjust. 

Layer height

Layer height sets the height of each layer in your print. It is like the resolution in a camera. The thicker the layer height, the lower the resolution giving your print less detail. The thinner the layer height, the higher the resolution bringing more detail into your print. A thinner layer height increases the chances of failure or gaps in your print. 

One rule of thumb you can use with regards to layer height is to use a height that is 20% smaller than your nozzle diameter. For example, if your nozzle is 0.3mm then you would not go past a height of 0.24mm. 

Print speed

This is how fast the print head moves when extruding filament. You want to print at an optimal speed depending on the filament and the model. 

You can print faster without compromising your print if it is a simple model with less detail. The more complex and detailed the model is, the slower you want to go. The best way to figure out the optimal speed is to experiment.

Print temperature

You also want to print at the right extrusion temperature for the type of filament you’re working with. In some cases you might need to print slightly under or over the filaments extrusion temperature. Here again, you need to experiment to find the optimal setting.

Fill density

Infill percentage or fill density is how much material is printed on the inside of a model. It determines how hollow and heavy a model is. The higher the percentage the more solid it is. If set to 100% then your model will be solid. 

Setting your infill too low can lead to a weak model that topples or droops as it’s printed. This inevitably causes layer gaps or holes. You want to set your infill high enough so your model supports itself. Cura printers have a Gradual Infill Steps setting that steps up the infill as you go higher in the print. 

Shell thickness

This is the thickness of the layers of the outer shell of the print before you infill. The thicker the outer layers are the sturdier your print will be, reducing the likelihood of print failure. 

Filament quality

While this is not a slicer or printer setting it does play a big role in the success of your prints. Using a better quality filament reduces the incidence of print failure.

We also highly recommend that you check out our post “Signs Of Bad PLA Filament: What To Do About It!

We’ve covered the bases in terms of preventing gaps in your 3D prints. But what about filling the ones that do occur?

What Filler Should I Use On 3D Prints?

Automotive body filler is typically used to fill holes or fix layer separation in 3D prints. The most common automotive fillers used include Bondo spot and putty, Bondo body filler, and Rust-Oleum Automotive 2-in-1 Filler. A popular alternative to automotive fillers is wood filler. 

Wood filler is a great alternative because it is odorless and easy to use. Like automotive fillers, it is quick drying and you can sand it within 15 to 30 minutes of application. Source

Also, check out “Can You Use Spackle On 3D Prints? How To Smooth A 3D Print!

How Do You Fill Gaps In PLA?

Gaps in PLA are filled with wood, automotive or epoxy fillers. The fillers are applied to the gaps before being sanded down to produce the desired finish. An alternative to using fillers is a 3D pen. With a 3D pen, filament rather than filler is applied to the gaps. As with filler, the filament is sanded to get the desired finish.

Generally, these are the steps to follow when using filler for filling gaps in PLA:

  1. Apply the filler to the desired areas. Apply just enough to cover the gaps but not so much that you lose the detail you want to keep and have to sand down a lot of filler afterward.
  2. Once you’ve applied filler to all the affected areas, wait for it to cure. Curing time depends on the filler so check the label.
  3. After it has cured start sanding with sandpaper. Go from a harder to softer grit sandpaper as you get closer to your desired finish.

What Can You Use For PLA Fillers?

Both automotive and wood fillers can be used as PLA fillers. Apoxie Sculpt is an alternative option to either wood or automotive fillers. Used in a variety of applications including bonding, sculpting and filling, the specific advantage of Apoxie is that it can be mixed and comes in multiple colors. This is especially useful for prints that will not be painted. 

Another advantage of Apoxie is that it is water soluble before it dries. This makes it particularly easy to sculpt and mold your print with it.   


I am a very well experienced techie civil engineer who's extensively interested in 3D printing technology and even more captivated by the potential of 3D printing livable structures

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