I ran into this exact problem last summer when I tried patching a seam on my garage roof. It was pushing 95°F and the TPO felt like it could fry an egg. I figured I’d just work fast and get it done, but the welds looked sketchy and didn’t hold up after a week. Ended up redoing it at sunrise a few days later—way easier, and the seams actually bonded right. If I had to do it again, I’d just wait for cooler temps or shade, even if it means dragging the job out. Trying to rush in the heat just made more work for me.
I get where you’re coming from, but I’ve actually had decent luck welding TPO in the heat—mid-90s, even. The trick for me was dialing back the welder temp and working in short bursts. Not ideal, but sometimes you just can’t wait for a cool spell. The seams held up fine, though I did have to keep a close eye on them for a few weeks. Maybe it’s just luck or the brand of membrane, but I wouldn’t rule out hot weather entirely.
