A few weeks ago, I picked up a POE Ether Thermo 6 long insulated air mattress at the REI garage sale with a reported bad valve. The valve was damaged and I though it was worth the gamble to try a repair.
I ordered a Therm-a-Rest valve repair kit. It came with a tube of hot glue that you put in hot water for a few minutes and go-for-broke to install the valve before it cools. The instructions for the Therm-a-Rest said to grab the old valve and give it a good jerk to remove it. That worked with the POE mattress too, which has an aluminum valve in a block of plastic, much like the Therm-a-Rest. I was surprised how easy it was to pull out. I used channel-lock pliers and gave it a twist as I pulled.
The Therm-a-Rest valve is about 1/8" smaller in diameter than the POE valve and I assumed that the Therm-a-Rest glue wouldn't fill the gap. I tried silicone adhesive and let it dry overnight. That didn't work-- the silicone just peeled free of the plastic on the valve and the air mattress.
Plan B: JB Weld epoxy. JB Weld is great stuff. When we run out of that and duct tape, sheet rock screws and zip ties, our civilization will come to a grinding halt.
I digress. I mixed up the epoxy and folded the air mattress in half lengthwise, and then rolled it up so the valve was on the outside. I put some shipping tape around it to keep it rolled. This was all to keep the valve hole pointed up while the glue dried. I buttered the valve neck with epoxy and rotated it a bit as I pushed it into the air mattress. You need to watch the depth carefully, so the valve cap can go down far enough to seat. Once in place, I put a strip of shipping tape up and over the valve to keep it from sinking further. I let it dry overnight and it held nicely.
So I inflated the mattress and let it sit. I found that the valve wasn't the only problem. Upstairs to the bathtub and a leak-finding session. Of course, I found multiple leaks in the bottom side of the lower section. Scratching head.... shorter!
Back down to the basement, measured for my side sleeping preference, and lopped 13" (and 5oz) off the bottom. Got out the clothes iron, turned off the steam features and while it was warming up, I opened the bottom of the mattress and tucked 3/4" of the poly insulation up into each tube, folding it over a bit and making sure that there were no strands left on the fabric where I wanted to create the seam. This was easier than I imagined. I thought it would be a chore to get the insulation off the fabric, but it peeled free with little left over.
I put an old towel on top of the washing machine lid and started sealing the bottom edge, only working on a couple tubes at a time, so the insulation wouldn't shift and get into the seam. I went with a 3/8" seam, about double what the manufacturer used, assuming it would be stronger and more forgiving of my first-try technique. I made diamond points into the vertical seams to reinforce things a bit and avoid 90 degree angles with more stress on the corners. I had the iron set on the highest temp and it went well. It was almost too easy!
I let it cool, filled it up tight, and everything held :) The finished project came out to 49"x20" and 15.3oz. Total cost $17. It's gonna be a comfy summer!