Introduction: Testing the Best Glue for PLA 3D Printed Parts


I wanted to know what is the best glue for PLA (Polylactic acid). So I did some Googling and found that an adhesive called Weld-On 16 is the best. However I have a bunch of adhesives kicking around and I was wondering how well they would work.

What better way than to do some testing of my own.

There are other ways to join PLA together like friction welding but I'm going to concentrate my testing on off the shelf glues.

Step 1: Materials

In no particular order the following are the adhesives I am testing:

  • Weld-On #16
  • Epoxy
  • Polyurethane Glue
  • CA - Cyanoacrylate (Crazy Glue)
  • All Purpose Goop
  • Plastic Model Cement
  • Contact Cement

The PLA I used was just some regular generic PLA.

The pieces were printed on the Anycubic Mega-S printer (affiliate link).

Step 2: Testing Methodology

I struggled with coming up with a testing methodology, as there can be a few different variables to account for. The variables I found that impacted the testing the most were the flexibility of the PLA pieces and surface preparation (sanding).

I ended up retesting some glues but more on that later after my initial testing.

I printed off a bunch of flat pieces of PLA, 40 mm x 20 mm wide by 3 mm thick.

Two tests would be performed on each glue, one on sanded PLA and other on un-sanded PLA.

All the PLA pieces were then glued using the different adhesives, clamped and left to fully cure as per the directions of each glue.

Step 3: The Results

Once the glues were all cured and set, I did some destructive testing by first pulling on the pieces to try and separate them. If the held up, I then applied more force with a twisting and prying motion. I also included how fast the glue sets as that can be important if you have parts that can't be clamped.

The results are as follows as ranked from best to worst for strength:

  1. Weld-On 16 - Excellent bond, it really was like it was welded, the PLA broke before the glue. Very Fast setting.
  2. CA (Superglue) - Excellent bond, the PLA broke before the glue. Fast setting.
  3. Contact Cement - Excellent bond, the PLA broke before the glue. Very Fast setting, immediate bond.
  4. Model Cement - Ok bond, the glue broke, PLA was intact. Slow setting.
  5. All Purpose Goop - Bad bond, the glue broke, PLA was intact. Slow setting.
  6. Epoxy* - Bad bond, the glue broke, PLA was intact. Fast or slow setting depending on type.
  7. Polyurethane Glue* - Bad bond, the glue broke, PLA was intact. Very slow setting.

*These glues I expected to perform much better and this was due to the pieces of PLA were flexible and not sanded rough enough. The flex in the PLA allows for the glues to "peel" away from the PLA pieces.

At this point I wasn't happy with the results and decided to do more testing...

Step 4: More Testing and the Results

I revised my testing and printed off some rectangle boxes and really roughly sanded them to give the PLA the best chance possible for success. I've had great luck with epoxy and polyurethane glues joining different types of materials together so I want to be see how I could get them to join PLA successfully.

The results of this test were much more promising, the combination of the rigid PLA and rough sanding made the PLA pieces very hard to break, I was unable to break the glue joint with my hands. I also retested the Plastic Model Cement to make sure and it broke at the glue seam so not really much improvement from the last test.

I also re-tested the epoxy and polyurethane glue with the flexible PLA pieces by sanding them much rougher than the first test. The results were much better with the glues holding stronger and with the pieces of PLA breaking first. However I was still able to break the bond between the glue and PLA for both Polyurethane and Epoxy.

Updated Rankings:

  1. Weld-On 16
  2. CA (Superglue)
  3. Contact Cement
  4. Epoxy - coarsely sanded and rigid applications
  5. Polyurethane - coarsely sanded and rigid applications
  6. Plastic Model Cement
  7. All Purpose Goop - IMO don't bother

So in summary it depends on the situation but the general rule is the rougher the pieces of PLA are sanded and the more rigid the pieces of PLA the better the glues will perform, i.e. proper surface preparation.

Weld-On 16 actually melts the PLA and the resulting solid bond is almost PLA to PLA so it holds incredibly well. I personally would use the top three glues when gluing PLA to PLA.

I did a video if you are interested in watching all the testing I did: