Originally Posted by
dddd
Firstly, even using Rema patch kits exclusively, the bond strength varies a lot, a long cry from the patch being "part of the tube".
I see creeping patch failures often enough even after all the proper instructions were followed. Many tubes don't give such good adhesion.
I have tubes in my tires and in my box o' tubes that have as many as 30 patches on them. I patch around 100 per year and I've been riding bikes for 30 plus years. If creeping patches were a problem, I suspect that I'd have seen some by now. The only patches that I've had fail have failed because I rushed the job and didn't allow the solvent to evaporate or I contaminated the glue by touching it. The fact that the bond is instantaneous and permanent is sometimes a problem if you don't get the patch oriented properly.
Originally Posted by
dddd
The only "manipulation" of the glue is to spread it around, hopefully with the solvent having a bit of time to do it's thing before becoming almost dry (why thickened glue doesn't work as well, but works acceptably if spread on thickly at first, giving more time to "etch" into the tube surface).
By 'spreading it around' with a piece of plastic you
are manipulating it. Put it on, let the solvent evaporate, and stick the patch to it. That's all it takes and the patch is permanently in place. If you try to remove it, you'll likely rip the tube rather than pull the patch off. I know because I've done exactly that.
Originally Posted by
dddd
The rubber compound isn't "particularly water absorbent", but the solvent is, and the bond can be compromised (why auto patching instructions specifically warn against this, and most patch kits say "allow to dry", not "you may accelerate drying by blowing on it".
The solvent used is xylene or toluene. Both are highly hydrophobic and do not mix well with water nor absorb water. Yes, the instructions say to allow it to dry but that is mostly an admonition against doing something silly like setting it on fire or breathing the vapors or trying to use an air nozzle to blow the solvent away (with the vulcanizing fluid). I don't blow on the vulcanizing agent myself because the solvent will evaporate quickly enough without extra help but blowing on it won't hurt anything.
Edit: The
Rema document on patching says not to blow on vulcanizing fluid with a heat gun because this will harden the surface and allow wet fluid to lurk under the surface. They also say to not use air from a compressor because the air is contaminated with oils which will interfere with the bond. I'd suspect that using polyethylene which is what most plastic films are made of could cause a similar problem.