Welding Plastics

The following process allows you to make structural repairs on most types of plastic components. The process is similar to gas welding. Caution: Plastic particles can be dangerous. Always were safety goggles when working with power tools.

Plastics are of two basic types: thermo-plastic plastics and thermo-setting plastics. Thermo-setting plastics include fibre glass and are not weldable because heat does not soften them. Most plastics used on cars, trucks, vans and SUVs are thermo-plastic plastics.

First you need to identify the type of plastic you want to weld. Most components have a code stamped on the back. This code is put there for recycling purposes but you can use it to find out what type of plastic you have for welding purposes. Here are the basic codes:

Your plastic welding kit will include all of the components needed, including the heat gun and the various welding rods for the above plastics. Tip: if you cannot identify what type of plastic your part is made of, find a rod that has a similar look and feel. Weld with that rod on an area that will not been seen and experiment to discover the correct material.

First sand off the paint from around the area you will be welding. Using your Dremel tool with the rotary cutting tool from the kit attached, form a 90-degree, V-shaped groove along the length of the crack. Use your electric drill to drill into the ends of the crack to prevent it from spreading.

To prepare the crack for welding, attach the burring tool to your Dremel tool and using a high speed, start a groove about 10mm beyond the end of the crack. Increase the depth progressively. At the correct depth, the welding rod should rest nicely in the groove with the upper curved face of the weld rod protruding 1mm to 2mm above the surface of the repair. This allows room enough for rod penetration and for the weld dressing. It also cuts down on the need for fillers.

The weld kits comes with a chart that tells you what temperature to use for the different types of welds and plastics. Reference your setting before you begin to tack weld and set the heat gun accordingly.

Fit the tack weld nozzle to the heat gun. Draw it along the base of each "V" groove. Hold the nozzle so its toe contacts the base of the groove and the heal is slightly raised. As you draw the nozzle along, the hot air will melt the plastic below the nozzle's heel; the toe brings the soft plastic together. Because the base of the "V" is quite thin, do not put pressure on the heat gun - you want to avoid pushing through it.

As you tack weld, you can adjust for minor misalignments. Simply hold the sections in place until the weld has formed and cools.