Introduction: Automotive Plastic Welding Repair

About: I am an automation engineer but I will give anything a go. I don't know if you call if pessimism or just being an engineer, but I look for problems everywhere, then I look for some weird, left field way to sol…

This is the inside of my boot lid.

I drive a commercial 4x4 and somewhere in its life, something heavy fell against the door and cracked the plastic door card.

The crack started small but over time and a large amount of off road driving through construction sites and quarries has made the crack so large that the door card has started to fall off.

I looked for a replacement and the cheapest I found was over E250, used!

Time for the Maguyver in me to come out, let's make a weld repair!!!

Step 1: Let's See What We Are Working With

The first job was to remove the door card, it would be nearly impossible to repair it in place and even though I wasn't looking to bring it back to looking new, I wanted to make the repair to the back as it doesn't look too great when finished.

Using a prybar, I removed the snap fasteners and dropped the cover off.

There was some sound deadening bonded to the inside so I cut this, I forgot to take a picture but I stitched this back together with zip ties before I replaced the part.

The crack was not aligned so the first job is to make the sides of the crack line up as best you can.

Step 2: Welding

We are going to use a soldering iron with a large tip to make the weld.

WARNING!!!! Melting plastic releases toxic gasses, depending on the plastic in question it may even release cyanide so work outside or with extraction and wear a mask.

Also, the soldering iron and ultimately the plastic will get hot so be careful of burns.

Start out with a low wattage soldering iron, maybe 25 or 30W, the hotter irons will vaporize the plastic and do more damage than repair.

Turn the iron so the flat is pointing to the sky and press very gently into the plastic. You want to melt about 50% of the way through.

Start before the end of the crack and continue past both ends, this will seal the ends of the crack and stop it spreading beyond the repair.

Keep moving the iron and pushing the newly melted plastic towards the last melt, this will produce the "stack of pennies" look you get with TIG welding and is very strong.

Step 3: Dressing

Once complete, the plastic repair will be strong but the crack will still be visible on the other side.

To clean this up a little, I flipped the part over and using the flat of the iron, melted the joint a little.

This looked like a line of sealer in the end but it closed up the crack and leveled off 2 high points left from the repair.

It's never going to win a beauty pageant but it is fixed, strong and it was free!

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