Plastic Welding Technique provides extreme strength

The following information was provided to a customer recently asking a “Technical Question – Weld Strength” (hot air plastic welding) –

The customer thought the reply he received was very helpful, so we’ve decided to share this with you all –
(Hi Tim, Fantastic, substantive reply. Rare these days. Thank you for that and the links to additional resources. Have a wonderful day, Tom)

Question :

I was impressed by your video on Youtube. Thought you might be able to answer a basic technical question for me regarding strength of a plastic weld seam.

My question:
After the weld is completed, assuming it was done as expertly as is possible by anyone, what percentage of strength would you expect the welded seam to have, compared to the material in the center of either board? An exact figure is not needed. I’m trying to understand the basic concept of whether plastic welds can perform as well as a non-welded piece of HDPE could. If you could send or refer me to any documentation on the subject, that would be wonderful.
Thanks for your help, Tom

Answer :

Hi Tom,

Thanks for your email.

Plastic welding, carried out correctly, can provide extreme strength. It is used in repair of automotive parts, including plastic bumber bars, which are required to hold high strength after welding.

Equipment and the material itself can also have an impact on weld strength. Poor or incorrect welding procedure, eg. Poor weld area preparation, can result in poor weld strength. Also low grade material can also dictate welding results, as can incorrect welding rod selection.

Weld testing on the material first, using one of our Rod Test Kits – this helps the welder to select the most appropriate rod…. Also try welding it to itself. You can achieve best results with the most compatible welding rod materials – you cannot be more compatible when welding the material to itself – so a weld test to the parent material, from a slither of the parent material will display ‘best’ possible welding results of that meaterial – if this type of test shows a poor weld strength , then it shows either a low grade material or perhaps a material which has some kind of content filler. Which can sometimes impede weld quality.
Click here to see the Rod Test Kit

We have a great text book – its called ‘The Plastics Fix’ It is currently the most comprehensive plastics welding text manual available.
Click here to see the Plastics Fix text book

On one of our websites ( or on the home page – there is a bit more on ‘how to weld plastics’
Click here to see our detailed section on ‘How to Weld Plastics’    … It shows some short video clips covering each step..

We also supply tensile testers, which can be used to accurately test weld strength.. I have been able to weld at 98% strength of the parent, and while my own knowledge and training was achieved in Switzerland (to dvs worldwide welding standards ie. the technique we teach) – i am not welding all day everyday.
Click here to see our Weld Testing Equipment

I hope this is helpful.

Tim Fastnedge


VIDEO: How to Weld Plastics