Concrete Molding with Tough PLA on a MakerBot Replicator+

By Morgan Schwartz on

For many design projects, 3D printed parts made of plastics are not strong enough to withstand extreme impact, high heat or other stress factors. This can limit 3D printed parts, especially in PLA, to the prototyping phase of development. To put this challenge to the test, I created an experiment on concrete molding with tough PLA on a MakerBot Replicator+. This is what I found.

Experimenting with Tough PLA

For this experiment, I use 3D printing to create a mold for a more durable material, in this case refractory concrete. I then test this form in the intense environment of molten glass.

This idea originated from my background with glass art, where I often used molds made of graphite or metal that were expensive and not always ideal shapes. Using my experience with 3D printing and 3D design, I wanted to find a solution to this problem using the following steps:

Step 1: Designing the mold with SOLIDWORKS

Concrete Molding Using Tough PLAThe first step was to design the form for the negative mold using SOLIDWORKS. For this, I made a square and extruded it with an outward facing draft angle. I then hollowed out this shape to the desired wall thickness using the shell feature. On the inside of the box, I extruded a star pattern with an inward draft angle as my desired mold shape. The finished part is essentially a hollow cup. The draft angles are to help with removal of the concrete, much like a muffin mold is angled in for removal of baked goods.

Step 2: Printing the part with Tough PLA

Concrete Molding Using Tough PLA Img 2-323078-edited.pngNext, I printed the part I designed on the MakerBot Replicator+ 3D printer using Tough PLA material, comparable in strength and durability to ABS. While Tough PLA does require its own smart extruder print head, the print head and material is simple to install, and the print quality was indistinguishable from the regular PLA on our MakerBot.

Step 3: Molding with concrete

Once I had the part finished, I applied a mold release to fill in some of the layer lines and added lubrication to release the concrete from the mold. For this experiment, I used petroleum jelly applied with my fingers and a Q-tip.

Next, I mixed about two cups of high-temperature refractory cement, used for wood stoves and ovens, with a small amount of water until it took on a smooth, mixable consistency. I then poured the concrete into the mold and shook it gently until the concrete settled, and the top of the form looked smooth.

Concrete Molding Using Tough PLA Img  3.jpg Concrete Molding Using Tough PLA Img 4.png

The next day, after adequate curing time, I removed the cast concrete form from the mold. Heating the tough PLA  with a heat gun and pulling with a needle-nosed pliers helped with this process. The final form was slightly rough, but it did reveal the shape I was after.

Concrete Molding Using Tough PLA Img 5.jpg Concrete Molding Using Tough PLA Img 6.jpg

>> Watch our on-demand webinar for more on molding, layup and casting applications

Step 4: Testing with molten glass

Now, it’s time to see how this concrete form holds up to molten glass. I chose this shape to mimic an optic mold, which is a tool used to make glass millefiori. Millifiori is an Italian term for “thousand flowers.” For this technique, an artist makes a multicolored shape which is then drawn out to finer cane that can be nipped to reveal an extruded image in the cross section of the cane. Millefiori cane can then be bundled or used as components to make even more complex images.

For this stage of this experiment, I prepped a rod of white glass with a thick layer of black glass over it. I then sprayed the concrete mold with some water to help reduce dust and direct heat. I then got the glass very hot before plunging it into the concrete mold I created.  I was left with my desired star shape.

The angles on the glass were rougher than I was hoping, so using a butter knife, I cleaned up the ridge lines and coated the star shape with another layer of white glass. A final layer of black glass was applied before finally heating the form and stretching it out to about 12” of cane with a star in the cross-section. This completed a basic six-pointed star millefiori.

To take this a step further, I then bundled multiple short sections of this cane inside a clear piece of glass tubing and pulled it out again creating a more complex clustered pattern. This proved my hypothesis that you could make traditional glass millefiori using a 3D printed mold.

Concrete Molding Using Tough PLA Img 7-256245-edited.jpg Concrete Molding Using Tough PLA Img 8-329034-edited.jpg Concrete Molding Using Tough PLA Img 9-379285-edited.jpg Concrete Molding Using Tough PLA Img 10-156037-edited.jpg
Concrete Molding Using Tough PLA Img 11-199651-edited.jpg Concrete Molding Using Tough PLA Img 12.jpg Concrete Molding Using Tough PLA Img 13.jpg

Single star and clustered star millifiori cane with components and a finished pendant.


The final product was not perfect, however, I did have some interesting results while developing this process. The concrete I used was too brittle and course in texture to be ideal for this application and to keep nice crisp edges in the mold. There may be other higher quality refractory materials available that are better suited for this application. My guess is that this process would be better suited for casting material directly for the final form such as for silicone or concrete sculpture or other glass processes such as fusing or frit casting.

While the results weren’t a complete success, I did successfully produce a ridged and durable form from a Tough PLA 3D printed part that survived through extreme heat and abuse, which was the goal of this experiment. I look forward to trying this application with other forms and materials in the future.

Trying to decide which material is right for your industry and application? Download our 3D Printing Material Guide to compare textile strength and toughness of Stratasys materials.