How to weld polyethylene

Written by alexis rohlin
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Polythene is a type of high-density plastic that is used to make kayaks, aquariums, hauling tanks, pipes and drain culverts. It can be used in a number of applications that require a lightweight, durable, noncorrosive material that is a poor electrical conductor. You can build items with polythene or repair them by welding the material with polythene spline. Polythene is welded together in the same way that metals are welded: a thin piece of the material is melted and used to fill the gap and make a joint.

Skill level:
Moderately Challenging

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Things you need

  • Safety goggles
  • Face mask
  • Electric grinder/sander
  • Cloth
  • HDPE welding gun
  • 3/16-inch polythene weld spline
  • Welding spline guide

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  1. 1

    Put on your safety goggles and face mask. Sand the surface areas of the polythene that you are going to weld together until they are both rough to the touch. Use the grinder to sand a 30-degree angle, or bevel, onto both pieces that you are going to weld together if you are going to weld a butt, edge or corner weld. Overlapping pieces or fillet welds do not need this bevel ground into them. Wipe off the surfaces with a cloth to remove any debris made from grinding and sanding.

  2. 2

    Preheat the area you are going to weld with the HDPE welding gun by holding it at a 45-degree angle to the welded area, slowly moving it up and down the weld joint area. Allow the hot air that the weld gun blows to hit the sanded surface of both pieces of polythene for two minutes.

  3. 3

    Insert the sleeve of the welding spline guide onto the end of the polythene welding spline. Touch the guide end of the spline onto the preheated joint. Hold the welding rod of the HDPE welding gun at a 45-degree angle to the polythene, about 1/4 inch to 3/4 inch above the material. Tack the polythene pieces together by placing small amounts, about 1 inch of melted spline, at both ends of the joint or gap between two pieces and in the centre of the joint. Hand-feed the weld spline into the joint of the polythene while taking care not to get your fingers too close as you may burn them on the hot material. The preheated polythene will make the spline start to melt. When it melts, start to move the spline over to the next tack section of the joint. Insert a new piece of welding spline.

  4. 4

    Place even pressure on the rod end of the welding gun, and when a bead of melted spline starts to form at the rod's end, begin to slowly move the welding gun up the polythene joint. Keep the bead visible along the edges of the welding rod as you go to ensure that you are placing enough melted spline into the joint to make it a strong weld. Allow hot air from the welding gun to blow onto the polythene. As you weld, lay down the melted spline at a rate of 1 inch every two seconds, moving down the joint at a rate of 4 inches per minute as you start to fill it in.

Tips and warnings

  • If you need to make another pass over the joint, take care not to overheat the polythene as this will create a weak weld. Let the polythene completely cool down before you make another pass to fill in any gaps that you may have missed during the first welding pass.
  • Work in a well-ventilated area as melting polythene will produce chemical fumes.

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