One of the most impressive aspects of plastic products, from small boxes to furniture, are the clean glue joints that make up each piece. While this work is normally done by professionals with years of practice, there’s no reason you can’t create clean glue joints with a few simple techniques and a little practice. This technique works the same for a variety of plastics from acrylic to polycarbonate. All it takes is a little effort and a few inexpensive tools to get started.
- Skill level:
Things you need
- Acrylic cement (low viscosity)
- Gap filling acrylic (medium viscosity)
- Syringe or squeeze bottle applicator
- Micro-tip applicator
- Gluing jig
- Blue painter's masking tape
- Grease pencil
After having the pieces cut to the sizes required for your project, remove any protective backing from pieces that are going to be glued together. The backing on the plastic can cause the glue to pool under it, which can cause blush marks (especially with polycarbonate). Blush marks are raised, white splotches and are difficult to remove. The backing can also become glued to your project.
If you’re using a squeeze bottle applicator, fill it up to the halfway point with acrylic cement. If you’re using the thicker Weld-On 16 cement, unscrew the top and place a Micro-tip applicator on the end of the tube. The cement is ready for application.
Inspect the surface of the plastic you’re joining together for dirt or anything else that will get caught in the glue joint. Next check the edge that will be glued to the surface for any imperfections that will keep it from joining completely flat to the other surface.
Set the gluing jig (a block that has a 90 degree angle) against the piece so it is perpendicular to the surface you’re gluing to. Clamp the upright piece to the jig (squeeze clamps work best). Make sure the edge and surface you’re joining are flush with one another. If you’re gluing a butt joint for a box, make sure the edge and surface are lined up before you cement the materials together.
If you tip the squeeze bottle over, glue may drip on to your plastic as you work. To avoid drips, squeeze the bottle, raising the level of the liquid up to the rim and then slightly release your grip. A vacuum will form, keeping the liquid inside the bottle until you squeeze it out. Follow this procedure and you’ll keep the cement from spilling on to the surface of the plastic. If you’re using the thicker Weld-On 16, you don’t have to worry about spillage.
Place the tip of the squeeze bottle at the beginning of the joint formed by the two pieces of plastic. Gently squeeze the bottle while pulling the tip along the glue joint. If done correctly, you’ll see the cement come out and disappear into the joint. Capillary action pulls the cement into the tiny open spaces created by the saw use to cut the sheet plastic. If you’re using Weld-On 16, carefully lift the piece attached to the gluing jig and apply a thin line of cement. Set the jig and plastic carefully back in place. Allow the glue to dry at least an hour before handling your project.
Tips and warnings
- Acrylic cement is a solvent-based cement that fuses the plastic together.
- Store sealed cans and tubes of acrylic cement in zip-lock bags to avoid evaporation.
- You can trim the backing only off the area being cemented, leaving the majority of the backing on the plastic to protect against dripping glue. The backing must be removed wherever the cement comes in contact with the plastic.
- Use a grease pencil to mark gluing positions.
- Acrylic cement should be used in a well-ventilated area. Wear eye protection to avoid getting the cement in your eyes.
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