Why is my tube patch cracking?
 

I patched up a few tubes maybe 6 months ago and hanged them up in the garage. Today I tried using one of them and the tire patch is dry-cracked and leaking air:

https://cimg1.ibsrv.net/gimg/bikefor...c24721e38.jpeg
what could have caused this? This is a Rema patch.

That's really odd. I haven't seen that before. Is that a Rema patch, and did you use vulcanizing fluid?

Update: BTW, did you spread vulcanizing fluid over the patch?


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Is the tube fairly narrow for the tire/rim section volume? How old was the patch kit? Andy

At first glance it looks like a patch rubber that has dried out and when installed in the tire a rather narrow tube expanded past the patch's ability to do so. But this is nearly moot. What does another tube and patch kit cost? Andy (who has attached a patch to a SLIGHTLY expanded tube to avoid edge stresses)

Huh, that's a new one on me!

Any chance the patch and tube have been folded over and had a weight on it? Perhaps on a workbench with a heavy tool on top? Otherwise I too an at a loss, though I've think I've seen that on one of mine (in a few hundred patches; many stored or ignored for years).

I used rubber cement. Would that cause this cracking? I patched quite a few tubes with rubber cement and had zero issues until now.

I always use Rema Tip-Top patches and glue.
Even during the times of greatest crises and scarcity, I've always been able to have and keep a small stock of those.
When I use that (along with Schwalbe or Continental tubes), I'm certain enough that any problems are down to my poor work/preparation, not some other reason (I usually do a good job and very, very rarely see problems with my patching jobs).

Apart from that:
I make sure my tubes are not kept in direct sunlight or near some heating elements.
Likewise, I keep tubes in a plastic bag, to prevent any extra oxidation.
This way, I've been able to use 3 tubes (2 on the bike, one spare) in rotation (spare tube goes on a bike, the punctured tube gets patched and becomes a spare tube) for a decade, on a regular basis.

I bought the box of patches last year I believe. Do these have expiration dates?

Never seen this before. I have used completely dried up patches before. They were so dry that after I removed the foil I covered them in Vulcanizing Cement to get them soft again. They never cracked like this. I have not used Rubber Cement for patches but I know many people successfully do. I suspect that the patch was cracked or damaged before its application. I have seen tires come apart longitudinally like this...

It might. Vulcanizing fluid is different than rubber cement. Those patches should be used with vulcanizing fluid, preferably the stuff made by Rema. I use that myself. Rubber cement can get hard and brittle and it dries out depending on storage conditions. That may be the culprit.

Did you apply the rubber cement to the top of the patch? The photo suggests that. I have used heptane (for practical purposes naphtha) to remove soft rubber grip material. The rubber absorbed heptane and you were able to tear the thick rubber with fingers and take it off. Harder rubber in a tube, when I tried, did not react much to heptane. Now a solvent, such as heptane, is likely there in the rubber cement. I wonder whether the rubber on top of the patch were not soft enough to absorb the solvent from the cement. I am just speculating here. The bottom of the patch is obviously made not to react adversely to the solvent.

Apply vulcanizing cement only on the tube, never on the patch.

Once a generous amount of vulcanizing cement has dried on the tube, just press a patch onto it.

Ideally the tube should be installed right away so a fresh patch can mold into shape.

When hoarding leaky tubes, I mark the punctures so I can patch them only when I desperately need them.

No, I spred the cement on the inner tube, waited for it to dry for 5-10 minutes , and then put the patch on.

Mmm.... so you only patch the tube when you need to use it? When I patch one tube, I find myself wanting to patch all the other popped tubes in the garage too while I have all the supplies lying around and I'm waiting for the glue to set.

Is this the only tube of your spares that the patch cracked or are some of the others the same? I have never had this problem before. I patch tubes months before they get used, roll them up, sometimes with the patch folded and no problems. I do use Rema patches and fluid as they just seem to be the most reliable. The tube gets kept in a plastic bag in my seatpack mostly just to keep it from getting damaged from the constant rubbing that goes on in there. I know some here swear by using rubber cement, but my experience is that you can get a long-lasting patch sometimes but is much less reliable than the proper paired patch with vulcanizing fluid. Your patch has some mystery problem and IMO should just get a proper patch kit and spend your time riding rather than trying to figure out what went wrong.

The outward force of the air pressure will mash a fresh patch tightly against the tire ply or rim, making the patch more secure as pressure is applied to a new patch for months, compared to the 20 seconds of your thumbs.

I patch tubes when it's faster to do that than getting a new one from a local supplier. Speed is of essence as I flip/retail about 100 bikes every season.

When I have time to kill, I go work on the next bike to sell, not waste it on punctured tubes I regularly toss out when the pile gets too big.

I can't see how the choice of adhesive (rubber cement vs. Slime vs. Rema etc.) could make any difference, assuming the air is leaking through the cracked patch. The glue is just holding the patch to the tube, and unless air is leaking out around the edge of the patch, the glue is working.

Since we're all just speculating here, I'd guess there was some incident during the hanging storage time. Heavy weight folding the patch over, and the inflexible patch cracking perhaps. Odd that it affected just the patch, unless the patch had been stored next to a blower motor, perhaps in the warehouse or store from which it was purchased. That kind of ozone exposure might harden the rubber in the patch, while the tube to which the patch was attached was safe and sound inside a bicycle tire.