I was going to build a bunk over the dinette, but plans change, and luckily I hadn’t yet recycled the plastic interior end cap. Originally I had decided not to use the end cap, because it had been damaged by the previous owner upon removal. But plastic can be repaired, and here’s how I did it.
While the giant crack was the major concern, the first thing I knew I would need to do is stop all the little cracks from getting bigger. The best way to do this is by drilling a small hole at the end of each crack.
Next I needed to make sure the end cap was super clean so whatever I was going to use for repairing the crack would adhere to the plastic, so I went over it with soap and water, then TSP-PF, then denatured alcohol to remove any residue.
I research online quite a bit deciding how I would make this repair. There are many posts and videos on “plastic welding,” but I think that method is best for softer plastic like ABS. I tried plastic welding on a small crack, but this aged, brittle plastic just doesn’t take well to being melted by heat.
Next I thought about using a flexible backing and epoxy. I braced the crack from underneath as well as using some foil tape on the other side to make sure there was no movement during curing. Then I cut a patch of screen, and spread some two part epoxy over the crack before applying the screen. The idea was that the epoxy would stick to the end cap, and the screen would be embedded in the epoxy. I used foil tape and a brick to hold the screen and epoxy in place while it dried. I tested this method on the upper part of the crack. My thought was that I could finish the repair on the bottom (where separation was greater) with a different solution if this didn’t work well.
The epoxy and screen did work pretty well, but the more I thought about it, the more I worried that the cured epoxy would be brittle, and thus would just crack again with road vibration. The screen would likely keep the two pieces from separating, but the crack would become visible again from the front side. So I moved on to using something that I would actually need to purchase (what I had been avoiding by trying to use stuff I had on hand).
I also used a piece of steel (an Ikea wall cleat) across the entire front of the end cap to hold the crack closed and strengthen the structure.
I had used Fiber Fix rigid patch while on the road to repair a split in my turbo hose once, so I knew it did a great job of holding together, even under heat. The product had some pretty bad reviews online, but I think this was because people were not using it correctly. The product requires UV light to cure, and luckily, that is something I have a serious abundance of, living a mile closer to the sun here in Colorado. So I re-prepped the large bottom portion of the crack, and applied the patch as instructed. I then let the end cap sit in the bright Colorado sun for the entire day. The Fiber Fix cured extremely well, and I don’t think it will ever let go. It is seriously bonded to the plastic.
I then installed the end cap back into the Airstream, and finished the visible side with a couple of coats of Bondo before sanding smooth and painting.