Honestly, I’m not convinced just watching for gloss or flexibility is enough. I get that’s what a lot of folks say, but when I tried patching my TPO, it looked “ready” and then still peeled up a week later. I think the temp matters more than people admit, even if you don’t have a fancy heat gun. I ended up borrowing a friend’s IR thermometer and was surprised how much the temp jumped around, especially when the sun hit the roof or a breeze kicked up.
And about the color—my roof’s white, and it definitely seemed to heat up faster than the gray sample I practiced on. Maybe it’s just me, but I’d rather trust a temp reading than eyeball it. I know not everyone has the tools, but if you can borrow one, it takes a lot of the guesswork out. Otherwise, I’d say err on the side of less heat and go slower, even if it takes longer. Rushing it just made more work for me in the end.
That’s a good point about the color—my building has both white and tan TPO, and I’ve noticed the white heats up way faster on sunny days. Even with a temp gun, I still get nervous when it’s windy or the clouds roll in because the surface temp drops so fast. Out of curiosity, did you have any issues with seams after patching, or was it just the patch area peeling? I’ve seen more problems with overlap areas than with small repairs.
I’ve seen the same thing with white TPO—on a clear day, it’ll spike up 30-40 degrees hotter than tan, but then a cloud comes by and the temp gun reads way lower in seconds. Makes it tough to trust you’re welding at the right temp, especially if you’re working on a big patch and the sun keeps playing peekaboo. Wind’s even trickier. I’ve had welds that looked perfect, but then a gust would cool one edge and suddenly you’re chasing cold seams.
About the seams after patching—honestly, I’ve had more issues with overlap areas too. Especially on older roofs where the original welds are starting to get brittle. The patch itself usually holds up if you prep it right, but those factory seams or big overlaps can start to curl or even pop open if you’re not careful with your heat settings. I’m always a bit skeptical of “just follow the temp gun” advice because surface readings don’t tell you much about what’s happening underneath, especially with wind or if the membrane’s dirty.
One thing I’ve noticed: if I’m patching on a hot day and the roof’s already at 140°F or more, I’ll dial the welder down a notch or two. Otherwise, I risk frying the top layer and getting that weird bubbling or shrink-back at the edge of the patch. But if clouds roll in, suddenly you’re not getting any fusion at all unless you crank it back up. It’s a constant back-and-forth.
I wish there was a magic number for “too hot,” but honestly, I go more by feel and how the membrane reacts than by what the gun says. If you see smoke or the material starts looking glossy before you even touch it, that’s usually my cue to back off. But yeah, overlap seams are always my weak spot too—especially on repairs after hail or wind damage. They just never seem to weld as clean as fresh membrane.
Curious if anyone’s found a foolproof way to deal with those overlap issues, especially when weather keeps changing mid-job. I’ve tried everything from weighted rollers to pre-heating, but nothing’s perfect.
I’m always a bit skeptical of “just follow the temp gun” advice because surface readings don’t tell you much about what’s happening underneath, especially with wind or if the membrane’s dirty.
Totally agree—temp guns are helpful, but I’ve seen them lie to me more than once, especially with dust or even just a bit of morning dew. Overlap seams are tricky for me too. Weighted rollers help a bit, but I still get nervous about cold spots when the weather’s unpredictable. Sometimes I’ll do a quick test weld on scrap just to check how things are reacting that hour… not perfect, but better than guessing.
Yeah, I get what you mean about temp guns not telling the whole story. Last week, I was welding in the shade and my gun said it was fine, but the seam just wouldn’t bond right—turned out there was a thin layer of pollen messing with the read. I’ve started running my finger along the seam to feel for heat, not just relying on numbers. Sometimes it’s more about getting a feel for it than chasing perfect readings. Test welds on scrap have saved me more than once when the weather flips, too.