How to Glue PLA 3D Prints Together

by | Jan 14, 2021

Sometimes we need to print a big dimension part, that exceeds the 3d printer size. we need to print in separated objects, then connect them together with different angles. Gluing is the easiest way for this problem.

In this guide, you’ll learn how to glue PLA 3d prints in easy steps and the commonly used plastic glue for PLA material.

What is plastic glue?

plastic glue
Regular adhesives can not bond with plastic effectively due to its smooth and non-porous surface. To glue plastic, a special adhesive called plastic glue must be used. 

Plastic glues are best known for their bond strength and durability. It also has better resistance to temperature, chemical, and moisture exposure than common adhesives. When working with plastic, it is important to use plastic glue.

There are many different kinds of plastic glue. However, only a handful of them works well with PLA plastic.

How to choose the right PLA glue

First, make sure the plastic glue you intend to use is compatible with PLA. Otherwise, you might deform your project or burn a hole through it. You can check the product box or ask your local hardware store if it is compatible with PLA before buying it. 

Second, weigh your priorities. Do you prefer a quick turnaround time? Then a fast-curing plastic glue may be best for you. If precision matters more, a slower curing time would be more beneficial. 

Third, consider where the final product will be used. Will it be used both indoors and outdoors? If yes, you might want to use a temperature resistant and waterproof adhesive. Will your project be subject to frequent vibrations–like in a vehicle? If yes, choose an adhesive with a high bond strength and good impact and stress resistance.

We list all the pros and cons of PLA compatible glues below. It should help you choose the right fit for your project.

Common PLA glues we use

Below are a list of commonly-used PLA glues, and their pros and cons for reference.

1. Cyanoacrylate Glue

Cyanoacrylate Glue

Cyanoacrylate is a strong, fast-acting glue that works well with almost any material (including PLA). How fast is fast? Cyanoacrylate can bond two surfaces in as few as 10-20 seconds. If you are working on a rush project, this might be the right plastic glue for you. 

Cyanoacrylate is also very popular. In fact, you have probably already used this at least once in your life. You may know it as “crazy glue”, “instant glue”, or “super glue”. It is commonly used for general home repairs, industrial needs, and even medical emergencies. Regardless if you will choose this glue for your PLA project, it is a good idea to have this at home.

Pros

  • CompatibilityCost-effective 
  • Bond strength 
  • Bond speed 

Cons

  • Brittleness
  • Poor peel strength
  • Poor temperature resistance
  • Poor solvent resistance
  • Rapid bonding to skin

2. Two-Part Epoxy

Two-Part Epoxy
Epoxy glues are best known for their extraordinary strength and load resistance. In fact, epoxy glues are so strong, they are used to bind the blades of helicopters and wind turbines. If they can glue steel, they can definitely glue PLA plastic. 

There are two kinds of epoxy glues. Two-part epoxy, also called two-component epoxy, will require you to manually mix a resin and a hardener together. One-component epoxy comes pre-mixed but requires heat to activate the hardener. Since PLA has low heat resistance, using one-component epoxy with PLA is not ideal. Stick to two-part epoxy if you are gluing PLA.

Pros

  • Impressive bond strength
  • Good for filling gaps
  • Waterproof
  • Chemical resistant
  • Solvent resistant
  • Temperature resistant
  • Shock and impact resistant
  • High tensile strength

Cons

  • More expensive
  • Requires accurate mixing
  • Short pot-life when mixed
  • Long curing time
  • Hazardous to health

3. Urethanes

Urethanes
Urethane and polyurethane adhesives, also called PU adhesives, are known to be strong and versatile. Just like epoxy, they are called “reaction adhesives” because they cure through chemical reactions. 

Urethane adhesives have unique characteristics that set them apart from other plastic glues. For one, PU adhesives are waterproof and UV resistant, making them perfect for outdoor projects.  Moreover, they can be sanded, painted, and stained. If aesthetics matter to your project, you may wish to work with urethanes.

Urethane adhesives may not be as strong as epoxy, but they have impressive impact resistance. If urethane adhesives are good enough to hold a car’s windshield in place, surely they can effectively glue your PLA project too.

Pros

  • Fast and strong initial adhesion
  • Fast curing
  • Stress and impact resistant
  • Paintable
  • Temperature resistant (maximum 125 degrees celsius)
  • Chemical resistant
  • Water and moisture resistant
  • Suitable for both indoor and outdoor use

Cons

  • Lower bond strength compared to epoxies
  • Maximum shelf life of 1 year
  • Hazardous to health
  • Hazardous to environment
  • Subject to government regulation

4. Acetone

Acetone
While acetone is more commonly used as a cleaning or paint-stripping tool, some claim it is also possible to glue PLA together with the help of acetone. However, PLA in its pure form is not reactive to acetone. Only impure PLA with traces of ABS plastic can be solvent-weld with acetone.

Moreover, the strength of the bond depends on how much ABS is in the PLA material as well as the amount of acetone applied. It can also distort or warp the plastic being bonded. You may choose to use acetone as a bonding agent as an experiment, but it may be smarter to just use the right adhesive for PLA plastics.

Pros

  • Cost-effective
  • Invisible seams

Cons

  • Questionable bond strength
  • Will not work with pure PLA
  • May distort plastic
  • No prescribed curing time

PLA Gluing Step-By-Step

 1: Prepare your model

Whether you are designing one from scratch or downloaded a pre-designed template, check which parts you need to print and bond. Prepare all components and supplies needed for the next steps.

2: Prepare the surface for bondling

Adhesives work best with rough surfaces. Use sandpaper or steel wool to roughen up the surface you’d like to bond. Brush off or wipe the dust from the surface once you are done.

3: Check if your model is ready for gluing

Remove excess or uneven parts or edges with the help of flush cutters and needle-nose pliers. Make sure parts fit well together. If not, you may need to sand them down.

Remove all dirt, dust, and debris by wiping the surface clean. Avoid touching parts with your bare hands after.

4: Hold components in place

The last thing you would want when you are putting on glue is for your project to fall apart. That is why it is absolutely crucial to secure all components before gluing. 

This is similarly true for the curing process. Most adhesives take time to cure. It is important that your project keep its shape while curing. Otherwise, the glue may harden incorrectly and your project may end up deformed.

Depending on your project, you may use rubber bands, clamps, straps to secure each part together. For larger projects, you may need to use a combination of these.

polyurethane glue pla

5: Start gluing

Apply glue evenly throughout your model. Spot glue by putting a small amount of adhesive at regular intervals around your model. Use just the right amount of glue to avoid having to clean up the excess.

Start from the middle and work your way towards the edges. Make sure you have put glue on all seams.

6: Check all seams to make sure they are properly glued.

If there are seams that do not seem fully bonded and secure, apply step 5 to those seams.

7: Fill seams if needed
This step is completely optional. You can use Bondo to seal and smoothen gaps for a better looking final product.

8: Use an accelerating agent

This step is completely optional. Use an accelerating agent if you want to speed up curing.

9: Wait for the curing process to finish

Check the glue’s box for the curing time of your adhesive. If you don’t follow the prescribed curing time, it may lead to a weakened bond. Do not move your project or remove fasteners while curing is not yet complete.

10: Inspect your final product

Once the curing process is complete, remove the fasteners and inspect your final product. Test the strength of the bond to see if it fits your quality standards. Look at the aesthetics: are there rough edges that need sanding or excess glue that needs cleaning up?

Improve what needs to be improved. Repeat steps 4 to 9 if needed. Don’t stop until you satisfy your own quality standards.

Finishing

Finishing is the process of polishing your work to make it look as good and professionally done as possible. For gluing PLA, this can mean any of the following:

Friction Welding

You can use a Dremel rotary tool to friction weld PLA. Spin the two surfaces fast enough to melt into each other, creating a strong bond without adhesives. This is very useful when two printed parts don’t fit well together. By the end of the process, it will be hard to tell where each individual surface ends and begins.

Filling and Sealing

You can also use a Dremel or similar rotary tool to close gaps. Gently drag a spinning piece of PLA onto the seams you wish to weld. The heat will dissolve the PLA onto the seams, filling the gaps in successfully. This process is called friction surfacing.

Sanding and Polishing

To smoothen out the edges and surfaces of your project, sand them down. You can use 100-150 grit sandpaper.

After sanding, you can smoothen its appearance with the help of superglue or a heat gun. Use a heat gun with caution as PLA is more sensitive to heat than other plastics.

Tips You Need To Know

Some last-minute reminders to make gluing your PLA parts easy and effective:

1. Make sure your surface is clean and dry.

Remove all dust, dirt, oils, and residue with alcohol or a plastic cleaning agent. Once the plastic surface is clean, do not touch the surface with your bare hands to avoid the transfer of oils.

2. Roughen the surface.

Use sandpaper (120 to 200 grit) or steel wool. You can also use Loctite’s two-part plastic bonding system, as that comes with an activator that helps roughen up the surface. As with step 1, remove excess dust and debris by using a brush or gently wiping the surface clean.

3. Apply the right amount of glue.

To avoid putting too much glue, use a smaller squeeze bottle or applicator. You can even use a paintbrush or needlepoint as an applicator.

4. Prepare the glue as stated in the manual.

Read the instructions carefully. Some glues come with two parts and require manual mixing. Follow the exact mixing ratios stated in the box to maximize the effectiveness of the adhesive.

5. Follow the curing process.

It is important to secure components together with rubber bands, straps, or clamps while the curing process is ongoing. Read your instruction manuals to find out how long you have to wait for the glue to completely dry and cure. Do not touch or move your project before the curing process is complete.

6. Keep safe

Follow the safety precautions stated in the instruction manual. When in doubt, use gloves, eye protection, a mask, and protective clothing. It is also preferable to glue in a well-ventilated area.

7. Protect the surrounding area.

Wipe off any excess glue immediately before it hardens using isopropyl or denatured alcohol. Make sure your plastic glues are properly sealed and stored in a cool and dry location, preferably with a temperature between 75°F (24°C).

Summary

If you choose the right PLA glue and follow the steps. Gluing 3D printed PLA together will not be a hard task.  

Lastly, remember that finishing and post-processing PLA are equally important.