cross-posted from: https://lemmy.dbzer0.com/post/52150351 [https://lemmy.dbzer0.com/post/52150351] > My bicycle was simply sitting at rest indoors when it exploded. A slit about ~6mm long was in the tube. I thought it might be too big to patch, but I happen to have some quit big patches to try. I cleaned the area w/denatured alcohol then roughened the surface w/the sanding tool. I covered the whole patch footprint area with rubber cement. Around 90 sec. later applied the patch and lightly clamped it down. About 5 min later: installed the tube and inflated to 4.5 bar. > > Couple min later it exploded again. As the image shows, it blew exactly along the line of the original slit. AFAICT, I could not have applied this patch better. That is, the air went through the patch instead of around it. > > Why did this happen? The patch is thicker and harder than the tube. So if the adhesive does its job well, then I would expect the patch to be stronger than the rest of the tube. The elasticity is lower in the patch, so I suppose that must be the problem. > > So I have to wonder: would it be more or less effective to cut previously damaged spare tubes to use for patching, instead of a patch? I wonder if larger holes need patches with more elasticity. > > #### Rubber cement vs. contact glue > > Patch kits include a tiny tube of “rubber cement”. The instructions say to wait 3 min before applying the patch. That’s similar to contact glue instructions. The only difference is contact glue instructions direct us to glue BOTH surfaces then press them together a few min later, whereas the repair kits never say to put glue on the patch (why is that?). > > Are the two glues chemically different? I ask because it may not make sense for me to buy another patch kit when I happen to have a very big tube of contact glue for shoe repair. >