PLA is beautiful and gluing has been a topic on some of our favorite manufacturer’s channels. For example, Stefan from the CNC kitchen and Joel the 3D Printing Nerd.
Here is some information from them along with my own experiences. Most of these glues are not exactly specific to PLA and work with many other materials as well. Be careful with PLA containing infill, although this can seriously alter the properties.
Which adhesive to use for PLA?
The easiest way to glue PLA is to use an adhesive, so the question is what kind of adhesive to use. We have tested different types of adhesives and can recommend the following: Cyanoacrylate and special adhesives for plastics. However, this only works reliably and durably if you use plastic glue with solvents. Normal modeling glue or glue on a purely biological basis, unfortunately, does not work or only to a very limited extent. We use UHU-Hart to glue together parts printed with PLA.
Step 1: Safety first!
Some of these methods work with chemicals that can irritate the skin (resin, cyanoacrylate), have irritating fumes (acetone), are flammable (acetone), and others.
Use proper protection when working with these! Protect your eyes and respiratory tract, as well as gloves if necessary. Read the manual for the products you are working with!
For most glues, it is advisable to prepare the surface: sand to increase surface area, remove grease from fingerprints, etc. Follow the manual!
Yes, “one type for all” is also a solution for PLA: Superglue. However, look for the type you get! Some are clearly better than others and using an accelerator can change the properties of the glue spot. Along with talcum powder, CA glue can easily fill gaps.
CA is not stable under heat and when heated too much it breaks down into a rather noxious smoke! This can be useful for breaking metal-CA-metal bonds in machining small parts, but keep this in mind if you want to use inserts or plastic insole parts in the same areas! Do not bond with CA in these cases.
Epoxy is preferred for very hard bonding, a few droplets can stick a car on the roof. And it gets hot in the cure. If you get a slow-curing resin, you can safely use it to glue PLA without the part warping.
2-component urethanes offer strong yet flexible bonds and work great according to Joel. Their curing process is also exothermic, so be careful not to “cook” your part.
In similar vein come 2-stage putties like Green Stuff or Miliputt, which harden after mixing. Their heat generation is not too great and they allow you to easily fill gaps. My favorite stuff, however, is not the expensive molding putty, but the home depot stuff: things like Pattex Repair for that or UHU Repair Tutti Powerkitt harden in an hour, are surprisingly cheap and have a smooth surface.
We all know you can sand and glue ABS with acetone or an acetone-ABS suspension. Tom (Thomas Sanladerer) has done some experiments with it. He found that it works ALSO for PLA: apply some acetone in one spot and press the second piece (also prepared in this way) and they will fuse together after a while.
In Germany there is a type of glue commonly called “Kraftkleber” or “Alleskleber”, for example UHU Hart or Pattex Kraftkleber German. While they often stick to PLA, I personally don’t like their bonding power and often find them quite messy to work with.
Glue? Why glue is important?
What better way to combine parts than soldering or welding?! Often none. My personal favorite PLA glue of all time is PLA itself, using it as a PLA solder. This method also works for most other types of filament, but is not recommended for ABS and other plastics that give off fumes without wearing respiratory protection. Here the method is discussed step-by-step as follows:
- Take the pieces and make sure there is a cavity on both sides that can be filled.
- Take a soldering iron and set it to about 200°C.
- Take a piece of the PLA filament.
- Melt the filament with the soldering iron and use it as a solder when combining the two pieces. Make sure at least some of the filament gets into the cavities and sticks there – it can help to stick the soldering iron in the hole in there to force it to fuse with the filler/walls and press it together to fill goop pieces of hot PLA against the iron before pulling it out, pressing the pieces together.
- As the PLA cools and hardens, the joint is generally harder than the actual boundaries of the layer.
Instead of using a soldering iron, you could also use a 3D printing pen one that eats the filament, not one for PCL or some gel, but I don’t like those personally.
Which adhesives should be used for PLA?
Cyanoacrylate is the technical term for adhesives that we know as SuperGlue, or superglue. It is an adhesive that is suitable for all materials, including PLA. This adhesive, which we almost all have at home or in the workshop, makes it possible to glue PLA in a simple and fast way
Many adhesive brands offer special adhesives for plastics, as they tend to be a bit more difficult to glue. I personally tried UHU for hard plastics, but you can equally use another cyanoacrylate adhesive.
Bonding PLA with epoxy
If you decide to glue the PLA parts with epoxy resin, you will have 3 additional advantages:
- You get a stronger bond than with traditional glues and adhesives.
- You can fill small gaps if the two joining surfaces are not smooth enough or have cracks
- You can also use the epoxy to improve the surface finish of the parts with the epoxy smoothing technique (you apply an outer layer on the part to remove the marks of the 3D printed layer)
But you have to accept one major drawback, which is that epoxy preparation, handling, and application are much more cumbersome and must be done in a room that can get dirty and is well ventilated so you don’t breathe in the fumes it emits.
There are many epoxy resins available on the market to smooth 3D printed parts, and each does the job. This allows you to kill two birds with one stone. The most popular product I’ve tried is SmoothOn’s XTC-30 resin, and there’s the Spanish alternative from 3DSmooth. But for both gluing and smoothing, you can use any epoxy resin with the right consistency (you have to be able to apply it with a brush and work the piece for 10-15 minutes).
How to use a hot glue gun?
The hot glue gun is a must-have in any workshop. It is good for making quick connections, covering holes, gluing cardboard, insulating electronic components and much more. It’s not usually used for visible connections, but it’s especially useful for prototypes and in areas you can’t see. You can get hot glue guns on Amazon, prices are around €4 and up.
PLA can be glued with hot glue, the only thing to be aware of is that the plastic starts to soften at 60-70ºC, so you have to be careful that the areas of the parts you want to connect don’t get too hot.
Gluing PLA with Acetone
Gluing PLA with acetone is an experimental technique that you can discover in the video by Thomas Sanladerer, one of the most popular YouTubers involved in 3D printing.
Acetone is available in online stores, drugstores and specialty stores. Nail polish remover that contains acetone can also be used.
As you can see, the original intention of the video was to smooth the PLA parts with acetone, but the result is not very satisfactory. However, the surfaces of the parts become soft enough to be glued together.
The Dremel method for PLA welding
This technique does not require glue or any other material, it consists of friction welding the PLA with a Dremel or other rotary multi-function tool. A piece of filament is inserted into the mandrel of the Dremel and rotated into contact with the part so that the filament, melted by friction, fills the gaps and joins the PLA parts. We have the Dremel 3000, but any rotary tool will do.
You have to be able to personally test this way of gluing PLA, but no one was very convinced of it: it’s a bit cumbersome (you have to stop and change the filament every time it runs out), people didn’t get a good connection or result. Maybe for projects where areas of the part need to be filled in or where it can be sanded down later, it might work, but I don’t see the point of welding the parts this way instead of using one of the three methods above.