3D printing process occurs by placing layers on layers to make a part. Each layer is made up of roads that are the beads of plastic that is laid. This process creates many tiny creases, allowing water to seep in. 3D printing is not an ideal for making waterproof parts.

The diagram outlines why FDM printed parts cannot be waterproof from the print bed. These layers, and beads of plastic that make up the print, leave a numerous open voids and locations for water to permeate.

With that being said, it is possible to produce waterproof parts with 3D printing. In this experiment we are going to research FDM process of producing. But the other methods of 3D printing is more application to produce 3D printed waterproof parts. SLA and SLS can make waterproof parts since the method of fabrication relies on laser curing plastic onto the body of the part. This process produces a watertight part off the print bed. 

For this experiment, we are going to investigate how to make waterproof parts with post processing FDM parts. A common practice is to coat the part with epoxy. Epoxy will fill the gaps in the FDM printed parts that water can enter and provide a waterproof barrier. 

The experiment consist of a 3D printed cube, 5 cm by 5 cm by 5 cm. This cube is going to be printed out multiple different ways. There are a total of 6 cubes, with one cube printed in PLA plastic. Because this type of plastic is sugar-based, it will decay over time, thus making it a poor choice for any working part.  For the purpose of this experiment, however, it is a good baseline, since it is extremely easy to print with. 

The rest of the cubes are printed in PETG plastic. This is great plastic to print with and to use for functional part. It’s very commonly used in everyday life; one of the most common uses is for water bottles. 

All of the PETG cubes are printed on two different 3D printers and printed at different parameters that would affect their water-resistant properties. Testing was wall thickness, layer height, nozzle diameter and the difference between 3D printers. 

The Ender 5 printed with .2 mm layer height and has a nozzle diameter of .4mm. Lulzbot Taz 6 printed with a .3 mm layer height and has a nozzle diameter of .5mm.
Each printer setting was set to the same, so there can be constantly between the prints. Such as print speed, printing temperature, infill (35%) and other parameters. 

Each cube was submerged in water for 30 minutes under 15 centimeters of water. This test is to ANSI/IEC 60529-2004 “Degrees of Protection Provided by Enclosures”. This test used IP 7 water-resistant standards as the base line for this test. 

The six cubes were weighed before and after they were submerged. After the cubes where submerged and weighed, they were dried in a food dehumidifier for 24 hours.

After the cubes were dried, they were coated with JB Weld 5 Minute epoxy. Each cube was applied an average of 8 grams of epoxy. The epoxy was applied by a brush, and each side was painted on one at a time. 

 After the cubes’ epoxy cured, the same IP 7 water resistant test was repeated to the same cubes now epoxy coated. In Graph 3, all the weights are recorded in grams:

The differences between the water weight gained with and without the epoxy is shown in the graph.  It shows how much water each cube acquired when it wasn’t protected with epoxy, and how much the epoxy did to prevent water intrusion. 0.05 grams is the weight of a drop of water. 

To the left, cube 4 gained the most water, resulting from the holes in the top layer of the cube. This happened during the printing process— the plastic didn’t fully bridge the gap between the infill lines, creating holes.

FDM 3D printed parts are not waterproof. Precautions may be taken to make parts more water-resistant, but they are not inherently waterproof. This experiment showed exactly why: the parts have small defects and holes, with too many entry points for water intrusion. 

Coating the parts with epoxy is the right step for waterproofing parts, but 3D printing tolerances go up since there is a human interaction involved. This makes working with parts that need tight tolerances more difficult. 

There are other 3D printing methods that are more effective at making waterproof parts such as SLA or resin-based machines. FDM is not a good choice for this application.