How to Bond Plastics

Look for products with a recycling symbol. Different plastics require different adhesives. The simplest way to identify the type of plastic is by locating the recycling symbol on the product's label or packaging. This symbol is a triangle formed by three arrows; inside or beneath the triangle, there will be a number, letter, or both.

Learn how to bond plastics marked with number 6. The recycling symbol with the number 6 or PS indicates that the plastic is "polystyrene." This type of plastic bonds best with poly glue (also known as plastic glue), or specialized adhesives such as Loctite Epoxy Plastic Binder or Super Glue Plastic Fusion. Other effective adhesives include cyanoacrylate glue (also called "quick-drying glue") or epoxy glue.

Select an adhesive specifically for plastics marked with numbers 2, 4, or 5. If your material is marked with 2, 4, 5, HDPE, LDPE, PP, or UMHW, it is "polyethylene" or "polypropylene" plastic. These plastics are much harder to bond, and you need to find an adhesive that specifically mentions the type of plastic on the label, such as Loctite Plastics Bonding System or Scotch Weld DP 8010.

Choose the right adhesive for plastics marked with number 7 or 9. The group of synthetic plastics marked with 7, or ABS plastics marked with 9, can refer to various flexible plastics and may include additional letters to further categorize them. It is best to use epoxy glue or cyanoacrylate glue.

Try to distinguish the type of plastic by other means. If there is no recycling symbol, you will need to identify the plastic type of the item before choosing an adhesive. Here is a guide to help you complete this task:

• Lego bricks are made from "ABS" plastic, which bonds best with epoxy glue. Solvent-based adhesives for ABS plastic can also work, but they may distort the surface of the material.
• Fake glass, cheap toys, CD cases, and similar brittle plastic items are usually made from "polystyrene," which can be bonded with several types of adhesives. For the best result, use poly glue or adhesives specifically designed for plastic.
• For rigid plastics such as bottles, containers, bins, and food packaging, use adhesives specifically marketed for "polyethylene" and "polypropylene" plastics. Most common adhesives cannot bond these items, so don't assume that an adhesive labeled "for plastic" will work unless it specifies "polyethylene" or "polypropylene."

Learn more if you need to bond plastic to another material. If you need to bond plastic to wood, metal, glass, or even another type of plastic, further research is required. If you cannot find an answer online or seek help from a skilled craftsman, head to your hardware store to find the adhesive that you think will work after reviewing the steps above. Packaging usually indicates the materials that can be bonded to plastic.

• Visit the This to That website for general advice on which adhesive to use for bonding different materials. This advice is especially helpful for common plastics, particularly polystyrene.
• If you're unsure about the adhesive you've chosen, try using it on a scrap piece of the same material or apply it to a hidden corner of the object you're bonding.

Clean off any grease from the surface to be bonded. Wash with soap, use a cleaner designed for plastic, or soak the item in isopropyl alcohol. Make sure to dry it completely.

• Avoid touching the surface with bare hands afterward to reduce the transfer of oils.

Sand the bonding surface. Lightly sand the plastic surface with 120-200 grit sandpaper to create a bonding surface for the adhesive. Steel wool or sandcloth can also be used, but remember that only a light sanding is necessary.

Mix the two-part adhesive if necessary. Two-part "epoxy" glue will require mixing to activate its bonding properties. Carefully follow the instructions on the packaging as different epoxy types have specific mixing ratios. Some epoxy glues can be used for hours after mixing, while others need to be applied immediately.

• Refer to the section on Selecting the Right Adhesive to know what type to use. Skip this step if you're not using two-part adhesive.

Apply the adhesive to both surfaces. Use a small brush to apply a thin, even layer of glue to both surfaces that need to be bonded. For small pieces, like a broken part of a plastic model, a needle tip can be used.

• If using a solvent adhesive (not poly glue), first clamp the two items together, then use a syringe to apply a bead of glue along the seam between the pieces. This will allow the glue to be drawn into the gap. If you're using solvent glue on plastic pipes, refer to the section on Bonding Plastic Pipes.

Gently press the two items together. Press the two items to hold them in place and eliminate air bubbles. Do not press too hard, or the adhesive will spill out of the joint. If excess adhesive leaks out, make sure to wipe it off, unless you're using acrylic adhesive, as it will evaporate by itself.

Keep the two pieces completely fixed. Use clamps, vices, tape, or rubber bands to hold the pieces together. Refer to the instructions on the adhesive packaging for curing time. Depending on the type and brand of adhesive, the bond can form in as little as a few minutes or up to 24 hours.

• Many types of plastic adhesives continue to "increase in strength" for days or even weeks after application. Avoid applying pressure or heat to the bonded items for at least 24 hours, even if they appear to be securely bonded.

Identify the type of pipe. There are three main types of plastic pipes, each requiring specific adhesives. The easiest way to differentiate them is by looking for the recycling symbol on the pipe, which has a triangle of arrows, often accompanied by a number or letter indicating the type of plastic. Learn to use this information or other identification methods before choosing the adhesive.

• PVC pipes are commonly used in residential settings, though they should not be used for high-temperature applications or distribution. These pipes are typically white or gray for electrical or industrial uses. The recycling symbol for PVC is 6 or PVC.
• CPVC pipes are treated PVC pipes designed to withstand higher temperatures. They share the same recycling symbol as PVC (6 or PVC) but are often light yellow or cream-colored.
• ABS pipes are an older, more flexible type of pipe, usually black. These pipes are not suitable for carrying drinking water, and in some areas, their use for plumbing is prohibited. The recycling symbol for ABS is 9, ABS, or 7 (Other).
• PEX is the newest type of plastic pipe and comes in a variety of colors. PEX cannot be recycled or bonded; mechanical connectors must be used to join PEX pipes.

Select the appropriate adhesive. The material used to bond plastic pipes is called solvent adhesive. Find the right solvent adhesive after identifying the type of plastic pipe.

• ABS solvent adhesive is used to bond ABS pipes together. PVC and CPVC solvent adhesives are used for pipes made from the same material.
• Intermediate solvent adhesives are used to join ABS pipes with PVC pipes. The bright green color of the adhesive makes it easy to identify.
• If you cannot find a specialized product, multi-purpose solvent adhesives can also be used to bond PVC, CPVC, and ABS pipes together. First, identify the type of pipe to ensure it is not PEX, as PEX cannot be bonded and must be connected using mechanical tools.
• Check the adhesive packaging to ensure it is compatible with the pipe size you're working with.
• When connecting plastic pipes to metal pipes, you may need a specific adhesive for bonding that particular type of plastic to metal, or you may need to use a mechanical connection. Ask a hardware store employee for advice.

Follow proper ventilation safety measures. Primer and solvent-based adhesives release toxic fumes when used. It is advisable to work in a well-ventilated area (open doors, windows, etc.) or wear a respirator to block harmful organic chemical fumes.

Smooth the inner surface if the pipe has been cut. Insert 80-grit sandpaper into the pipe and sand both the inside and outside of the pipe where the adhesive will be applied. This step removes rough spots and sharp edges from the cutting process, which could trap plastic debris and cause blockages.

• Ensure the sandpaper follows the pipe’s shape before sanding.
• If sandpaper is unavailable, use a file or a utility knife to remove any visible sharp edges.

Mark the joint location if you’re connecting a curved pipe. If time is limited to adjust the pipes after applying adhesive, align the two pipes first, then mark the spot with a non-erasable marker. Rotate the pipes into the correct position before marking them.

Apply primer before bonding. Among the three types of pipes, PVC is the only material that requires primer, though CPVC also bonds better with it. Coat both the inside and outside of the pipe ends to be joined with PVC or CPVC primer (depending on the type). Allow it to dry for 10 seconds before proceeding.

Work quickly and neatly when applying solvent cement. Wear gloves and use a brush or cotton swab to apply a thin, even layer of cement to the inside and outside of the pipe ends to be joined. Apply only a thin, uniform coat; excess cement will be pushed inside the pipe and could cause future blockages.

Immediately connect the two pipes by rotating them a quarter turn from the marked position, then twist and hold them in place. Right after applying the solvent cement, position the pipes a quarter turn from the marked spot and rotate them until the marks align. If no marks were made, simply connect the pipes and rotate them a quarter turn. Hold them in place for about 15 seconds to allow the cement to set.

Adjust the length discrepancy by cutting to create space for attaching a new pipe section. The joint may contract slightly as the solvent cement dries. If the last pipe section is too short, cut it and extend it by adding a new fitting. If it’s too long, cut off a section and join the remaining pieces with a new fitting.

• Silicone adhesive is ineffective for plastic unless used purely for cosmetic purposes, as it doesn’t provide a solid bond.
• If acrylic glue accidentally drips onto the plastic where no bonding is needed, there’s no need to wipe it off. The adhesive will naturally evaporate.

• Always bond in a well-ventilated area or wear a respirator mask.

• 2 pieces of plastic
• sandpaper
• adhesive (see Choose the Right Adhesive)
• small brush
• clamps, vice, tape, or rubber bands.

For Plastic Pipe Bonding:

• plastic pipe section
• plastic pipe connector
• sandpaper
• PVC or CPVC primer (see the guide for details)
• solvent cement (see the guide for details)