Originally Posted by
dddd
Are your tubes perhaps stretching greatly to fill the inside of the inflated tire? This would tug at the edges of the patch, so can eventually lead to a creeping failure of the bond surface.
How about your sanding procedure? Are you getting it sanded down to a very dark flat black? Are you fully sanding down the seam lines?
The glue is best applied with a piece of plastic bag stretched over your finger. Also, the glue needs to be fairly fresh, and needs time to etch itself chemically into the rubber surface. The glue should thus be spread initially in a thick enough layer, slowly so it doesn't go dry quite so fast, and the glue spreading should stop before the surface tacks up.
Lastly, never breath on the glue, the glue attracts and absorbs moisture that can compromise the bond (this is much better known in the auto/truck tire repair world).
Always allow plenty of time for the glue to dry completely before applying the patch, or the patches may fall off.
And, I'll say it again, some tubes have a gummy texture and do not abrade cleanly, even after much continuous sanding. Such tubes aren't the best candidates for repair.
As I said before, stretching isn't a problem with a good quality patch because the patch isn't just adhered to the tube but actually part of the tube. Creeping of the bond isn't possible.
The glue should be applied directly from the tube and not manipulated after application. Just allow it to dry for as long as you can wait. You can't wait too long. Allowing the glue to dry overnight won't do any harm. Don't touch the patch with your fingers because it interferes with the bond. Water and water vapor shouldn't matter since the compounds aren't particularly water absorbent.