Patch fail! Advice?
Sorry, this is kind of elementary. Last night I was helping my son patch a tube (goathead puncture). It would have been faster (and apparently better) if I just did it myself, but I want him to learn so he can become self-sufficient on the road.
Anyways, he found the hole, roughed up the area, put the vulcanizing glue on (Park VP-1), and then when he put the patch on, he missed the hole. So we quick ripped it back off, put some more glue on, and slapped another patch on. Seemed to hold. So he put the tube&tire back together and pumped it up, 35psi (mtb front tire), seemed ok.
This morning, flat.
OK, so, any advice on how to recover from a patch fail like that? If the patch goes onto the vulcanizing fluid and then gets ripped off, is the area just unpatchable afterwards? Is this tube trashed now?
More generally, something I've always wondered. When you find a hole (which is usually hard enough to find and see when air is coming out, but completely invisible when deflated) how can you mark the location of the hole, in a way that will remain visible even through abrasion and applying glue, so you can confidently center the patch on the hole?
My two ideas (probably bad) are: white chalk -- but you have to make a fairly big bullseye and aim for the center. Or: use scissors to embiggen the hole to like 1-2mm diameter, so it's obvious.
Any other handy tips?