When it comes to adhesives, J-B Weld is much like any other in that it excels at bonding some items and isn't recommended for use on others. For many plastics, the original J-B Weld creates a strong bond that holds up over time provided that the item isn't required to flex or bend. J-B Weld is not designed for some types of plastic, but the company makes many other epoxies designed for specific situations involving many types of plastic.
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Preparing the Repair Site
Using J-B Weld on plastic requires that both project pieces are clean and free from grease, oils and residues. This holds true whether repairing a broken plastic component or adhering plastic to another surface, such as fiberglass or metal. Wipe down the areas to be bonded with rubbing alcohol or white vinegar, which removes greasy films that may not be otherwise evident.
If bonding two smooth areas together, first rough them up gently with some medium-grit sandpaper. Wipe away the residue with a damp paper towel.
J-B Weld Plastic Usage
Once you've prepped both surfaces to be bonded, it's time to prepare the J-B Weld. The original J-B Weld product comes in two tubes. Mixing their contents creates the epoxy that bonds things together. Squirt equal amounts from each tube onto a paper plate or another disposable material. Squirt out only as much as you'll need, as there's no way to put the materials back into their tubes, much like toothpaste.
Mix both substances together with a toothpick, cotton swab or plastic putty knife until thoroughly blended. Apply the mixture to the area you wish to bond on one of the pieces. Press the materials together.
Clamp the bonded items or find another way to keep the pieces together as the J-B Weld cures. The best clamping method varies depending on the shapes of the items being bonded. For flat items, a heavy weight may suffice, while in other instances, you may wish to squeeze the items in a vice or hold them together with rubber bands.
J-B Weld Cure Time
Although it sets in four to six hours, the J-B Weld cure time is 15 to 24 hours. Do not attempt to utilize the bonded item for at least 15 hours. If you need the bond to set faster, KwikWeld does the trick, although it's not quite as durable as the original J-B Weld.
Not for Certain Plastics
The original J-B Weld does not work well on polyethylene or polypropylene plastics. In many cases, these plastics are identified by the recycling codes on them. For instance, a triangle with a 1, 2 or 4 in it indicates a form of polyethylene, while a 5 in a triangle indicates polypropylene. In some cases, letters are used instead of numbers and triangles. PET, PETE, HDPE, LDPE and PE are all polyethylene, while PP stands for polypropylene.
These codes are usually found on the bottoms of plastic items, such as containers for food or laundry detergent. Polyethylene is often used for water or gas containers or garden sprayers. Polypropylene is a harder plastic, durable enough for use on some car radiator parts.
Using J-B Weld PlasticWeld or WaterWeld
J-B Weld offers a PlasticWeld product, geared toward bonding more types of plastics than the original J-B Weld formula. Although PlasticWeld is available in both an epoxy putty form and a two-part liquid epoxy, neither of these bond polyethylene or polypropylene plastic. The putty cures in three hours, while the liquid version cures in an hour.
WaterWeld is yet another plastic-ready product the company offers. It is ideal for PVC pipes or situations in which the plastic parts are wet or will get wet. Clean and rough up the surface of the PVC and then work the two-part epoxy putty together until it reaches a uniform color. Spread the putty over the areas being bonded.
For a leak in a pipe, press some into the hole using enough putty around the pipe to ensure the plug stays put once cured. WaterWeld sets in about 15 minutes and fully cures in an hour.