Ngtjyty

Is there any special technique for using self-adhesive puncture repair patches?

Today, I've had two different tubes fail within a minute of being inflated because the air pressure had split through the glue, effectively forming a little pipe from the puncture out to the edge of the patch. These were both patches that had been on the tube between one and three months, and I've had other patches fail the same way.

I figure I've not done anything catastrophically stupid, since the patches haven't been failing immediately. I've followed the instructions on the patches as closely as possible ("Lightly scuff tube with sandpaper. Peel backing from patch and press patch firmly onto tube. Tube must be clean and dry for patch to adhere." – that's it). They're decent quality patches (Park Tool GP-2).

I've never had any problems with old-school glue and patches. Is there something I'm missing or are pre-glued patches just useless pieces of excrement?

This kind of failure is basically the reason sticker-type patches have a reputation for not being reliable.

Scrupulously sanding the area and getting it as clean as possible (ie, with alcohol or other residue-free solvent, cleaner than anyone can probably get it on the side of the road) wards off the problem but doesn't eliminate it.

Sticker type patches are essentially bad products. You can't trust the tube long-term, so you really should change it back out when you get home, because if you don't you'll likely get another flat sooner or later when it fails.

Vulcanizing is superior. The system of carrying a spare tube and a vulcanizing patch kit, using the patch kit only if you get multiple flats in the same ride (should be a very rare occurrence), and patching your punctured tube when you get home so it can become your spare is popular and time-honored because it works and is cheap. You almost never actually wind up using the vulcanizing kit on the side of the road, and when you do it's no big deal because you've developed good technique. Vulcanizing patches make the tube as reliable as new, so it's fine to leave the tube in there and forget about it.

I believe pre-glued patches were always intended to be a temporary fix to get you home. When they first came out on the market I remember explicit warnings that these were not a permanent fix.

Waiting for glue to set up on the side of the road is a pain, and these were intended to solve that issue by providing a quick fix to get you moving again. Afterwards you should replace the tube or properly repair the puncture.

Once applied these patches are easy to peel off again (a good indicator that they are not permanent fixes). A bit of sandpaper can remove any residual adhesive and as a bonus the surface has now been prepared for gluing with a proper vulcanizing glue and patch.

I have always viewed them as an option of last resort when you have run out of tubes and you need to quickly patch a tube so that you can keep going.

I practice I would never trust them to last more than a week after application.