Bicycle Mechanics - Why can I not patch this tube?

Patching an inner tube is a simple process. Or at least it should be. I have a tube with the tiniest pinhole puncture that simply won't reseal. I've tried patching it several times with a proper patch kit, with the same result: the air pressure simply blows a hole in the patch. Having run out of patches, I cut up an old inner tube. The 'patches' that result from this are thicker, but just won't seal properly- air always leaks out from somewhere.

I've patched tubes before, and tried every conceivable method on this one with no effect. The hole is on the inside of the tube, so I've inspected the rim and found nothing that would repuncture the tyre. I'm loathed to buy a new tube for the sake of a pinhole, so what exactly am I doing wrong here?

The only thing I can possibly think of is that the tube may be too small for the width of the tyre: the tubes are marked 26x1.5/2.1 and while the tyres are 26x1.9, the tube is on the skinny side. Is it possible the tube/patch is being overstretched as it's inflated?

Your tire is within the tube's range and I've even used "undersized" tubes from time to time without an issue so I don't believe that is the cause of your problem. It is not clear whether the patches are developing a hole or just leaking around the edge. If they are developing a hole, there is something external causing that. Identify it and your should eliminate the issue. If you are getting leaks around the edge, you aren't preparing the tube adequately or are not getting the patch on properly. I assume you are using glue patches, correct?

I've had some tubes that refuse to be patched easily. I don't know if it's just the tube, or a result of the new style (ie. weak but enviro friendly) glues. What does seem to work on these is pressure. Got a spring clamp? Use it. Patch normally, clamp it, take it off after a while.

In my experience, I have never been able to patch a tube on the inner (rim) side. It flexes too much when inflating it, so the patch just won't hold.

Could be coating on the tube to prevent the rubber from reacting too fast to ozone and other stuff that might make it crack during storage. Or it could be one of those pesky seams. If the hole is right there, it allows for a small pocket to remain and air bleeds slowly into that pocket and eventually lifts the patch off. You might scuff that area flat with emory cloth more, and you might use some small amount of acetone to buff the spot before trying to use cement. Thinner patch will also stretch more easily to hold just long enough to prevent leaks until pressure pushes the patch tight against the tube.

But at some point, I usually scratch my head, toss out the old tube and get a new one.

The problem with ANY patch is that there's mold-release on the tube, and the adhesive sticks to the mold-release instead of the tube. That's why they put the abrasive paper in the patch kit; they want you to rub off the mold-release. Cleaning with acetone or equivalent makes the patch stick much better.

In my experience, I have never been able to patch a tube on the inner (rim) side. It flexes too much when inflating it, so the patch just won't hold.

My experience also.

Get a new tube. Patching the inside is a waste of time.

Its funny how diverse the views are surrounding flat repair and how one person's "must-do" is not that important to the next person. I've never heard that repairing a tube on the inner "rim side" was more challenging than repairing it on the outer "tire side." I've never found that it took that much pressure to get the patch to stick and patching over seams hasn't been a problem either.

After scraping the area around the puncture with the metal scrapper, I put glue on both the area surrounding the puncture (in the tube) and also on the patch (I read somewhere to put glue on both surfaces although a lot of instructions just day to put it on one surface). I find that a patch that is around 1 cm in diameter will be big enough for most punctures (I don't know if smallish patches work better than bigger patches). One big "must do" is to let the glue "gloss over" or dry for a bit before applying the patch, I think you could wait 10 minutes or more, but I usually get impatient after a couple of minutes. Sometimes I blow air on the glue to help it dry faster. After pressing the patch to the tube using my thumb and forefinger I inspect the repair. I'll gently roll the repair area in my fingers to see how it reacts to the stress. I don't know why (maybe I should use more glue initially, or maybe more pressure would help after all) but usually I find that some of the outer edge of the patch is not adhering completely to the tube. I apply some more glue into any gaps (and maybe use a toothpick to work it in deeper), give it a little more time to dry, press the patch to tube again, and inspect again, usually at this point it passes the "rolling fingers" test. The whole "re-glue the edges" deal is my "must do" and I've never had a patch-repair fail once it passes the test.

still no progress on the tube this morning. I left it clamped in a vice overnight, and while all seemed well and good inspecting it this morning, it developed a leak again at around 20psi. It seems the air always finds some tiny weak spot to enlarge and seep around the patch :S Is anyone else having problems with halfords' tubes? I'm half tempted to take it back and complain as if a tube can't be patched properly it's not fit for purpose as far as I'm concerned.

Can you still get hot patches in the UK? I don't think you can here in the US but that tube sounds like a good candidate for one the old fashiond "real" patches. I remember when hot patches became hard to get we would light the glue with a match after smearing it on the tube, but I think they finally made the glue so safe that it would no longer burn. For many years, a match, was essential to a quality tire repair.

I generally use an abrasive paper or cloth and sometimes denatured alcohol or acetone to clean the repair area these days if I'm working in my shop. Otherwise I have had success cleaning the area by simply scraping it with my pocket knife before applying the glue to both surfaces. In either case I apply the new "safe" glue to both the tube and the patch, let them sit for a bit, then apply the patch and roll it down with something. If there is time, and I am in the shop I will sometimes press the patch down with my old hot patch clamp and let it sit for a bit, just because it is there(just about any kind of clamp would work as well).

... it developed a leak again at around 20psi. ...
Were you testing it? Inflating it before installing?

Were you testing it? Inflating it before installing?

This was after installing it in the tyre.

Get a new tube.

I have come across a few tubes that would not take a patch no matter what I did to prepare the tube.

Finally fixed it :)

Got some self-adhesive patches from the LBS, who were as confused about the situation as I was. It seems the rubber compound in this particular tube (Halfords 26x1.5/2.1) and the rubber cement (also halfords) weren't talking to each other. The self-adhesive patches seem to have done the trick so far.

Edit: spoke too soon...

Subject: Patching Tubes
From: Jobst Brandt
Date: March 15, 2005
The question often arises whether tubes can be practically and safely patched. I suppose the question comes up because some riders have had leaky patches or they consider it an imprecise exercise. Either way, it need not be difficult if simple rules are followed.

Why patches come loose

Tubes are made in metal molds to which they would stick if mold release were not sprayed into the mold. The release agent is designed to prevent adhesion and it can do the same for patches, some of it having transfered on and into the surface of the tube. To make a patch stick reliably, mold release must be removed. For this reason patch kits have sand paper that is not there to roughen the surface but to remove it. Failure to remove the 'skin' of the tube is a main cause of leaky patches.
Tube surfaces often have ridges at mold joints and near the valve stem that prevent effective sanding. This usually presents no problem because rubber glue and the plasticity of the orange (REMA) patch material are enough to seal those gaps. However, a plastic disposable (BIC) razor works well to remove such ridges and, with handle removed, makes a handy addition to a patch kit.

Once mold release has been removed, rubber solution can be applied with the finger by wiping a thin film over the entire area that the patch is to cover. After the glue has dried, with no liquid or jelly remaining, leaving a tacky sheen, the patch can be pressed into place.

Patches can be made from tube material but this must be done carefully following the same procedure as preparing the tube. However, butyl tube material, unlike commercial patches, is impervious to rubber cement solvents and will not cure if the glue on the tube and patch is not completely dry. This presents a substantial problem.

Patches

Patches commonly have a metal foil cover on the sticky side and a cellophane or impervious paper cover on the back. The foil must be pulled off to expose the adhesion surface before pressing the patch into place. The backing paper or cellophane often has perforations so that it will split in half when tube and patch are manually stretched. This makes peeling the cover of the patch from inside to outside possible and prevents peeling a newly applied patch from the tube.
REMA patches, the most commonly available in bicycle shops, have a peculiarity that not all have. Their black center section exudes a brown gas that discolors light colored tire casings in daylight. This causes the brown blotches often seen on sidewalls of light colored tires.

Leaky Patches

Assuming a patch was properly installed, it may still leak after a few miles, if used immediately after patching. Because tubes are generally smaller than the inside of the tire to prevent wrinkles on installation, they stretch on inflation, as does the patch. The stretched tube under the patch wants to shrink away from the patch, and because there is no holding force from inflation pressure at the hole, the tube can gradually peel away from the patch starting at the hole, while the tube under the remainder of the patch is pressed against it by air pressure.
Flexing of rolling bias ply tires also loosens patches. Laying a standard 3.5x2 inch paper business card between tire and tube will show how severe this action is. After a hundred miles or so, the card will have been shredded into millimeter size confetti.

If the puncture is a 'snake bite', chances of a leak are greater. Pinch flats from insufficient inflation or overload are called snake bites because they usually cause two holes that roughly approximate the fang marks of a snake. Although a single patch will usually cover both holes, these will be closer to the edge of the patch and have a shorter separation path to its edge.

In a rolling tire, the patch and tube flex, shrink, and stretch making it easier for the tube to separate from a partially cured patch. To test how fast patches cure, a patch can be pulled off easily shortly after application, while it is practically impossible after a day or so. For reliable patches, the freshly patched tube should be put in reserve, while a reserve tube is installed. This allows a new patch more time to cure before being put into service.

A tube can be folded into as small a package as when it was new and practically airless, by sucking the air out while using the finger opposite the stem to prevent re-inflation. This is not done by inhaling but by puckering the cheeks. Although the powders inside tubes are not poisonous in the mouth, they are not good for the lungs, but then that's obvious.

Patch Removal

The best remedy for a leaky patch is to remove it and start over. However, after several days of curing, a patch is hard to remove. With heat supplied by a hot iron or heated frying pan at moderate temperature, patches come off easily. Pressing a patch against a hot surface with the thumb until the heat is felt will allow the patch be pulled off easily. Patch remnants can be cleaned off with rubber solution (patch glue) or sand paper.
Minutiæ

Separating patches are often hard to find because separation always stops at the edge, air pressure preventing further separation. Slow leaks that occur, often close when the tube is inflated outside a tire, so the offending patch cannot be found. Old tubes to be discarded often reveal patch separation when cut through the center of a patch with shears, to reveal talcum powder from the inside of the tube under most of the patch.
Although talcum powder on the outside of tubes does nothing useful, it is essential on the inside, where it is found in any butyl tube. Without it tubes would adhere to themselves after manufacture and not inflate properly. Externally, talcum may prevent adhesion to the tire, slight as it is, and may help prevent sudden air loss in the event of a puncture but it does nothing for the wellbeing of the tube. When inflated, tubes act like an integral part of tire casings with or without talcum.

Tires are less flexible at a patch so tread may wear slightly faster there, but patches have no effect on dynamic balance since wheels naturally have a greater imbalanced than patches can cause and have no effect on the heaviest position of the wheel which is either at the valve stem or the rim joint. Heat from braking can accelerate separation of a fresh patch but this generally does not pose a hazard because leaky patches usually cause only a slow leak.

Having posted that, I feel I must add to it one thing............


http://www.youtube.com/watch?v=uLso0ZBqOi4

I just took the entire wheel back to halfords for them to look at. The staff there were very helpful- they tried fixing the puncture themselves with the same outcome as I'd had. In the end even they gave up and replaced the tube for me.

Did you let the glue dry? Dumb question, but I have to ask.

Did you let the glue dry? Dumb question, but I have to ask.

I tried every possible method- letting the glue dry, sticking the patch when tacky, glueing both patch and tube etc etc. I've patched tubes before with no difficulty whatsoever, but this one didn't want to patch no matter who attempted.

Not to be a jerk - but tubes are 6 bucks - replace it and ride!!

Not to be a jerk - but tubes are 6 bucks - replace it and ride!!

Good idea....send him $6 bucks.

Not to be a jerk - but tubes are 6 bucks - replace it and ride!!

Sometimes it is easy to get caught up in the challenge. Just replacing the tube would feel like a cop-out once a couple of attempts at repair have failed. I would probably still be trying to make that old tube hold air, even if I did put a new one on the bike...:lol::lol:

Many attempts at the same site could have made it hard or impossible to patch it. It may not be possible to remove all the residue.

My technique is:

- scrape the area with emory paper or sand paper
- spread glue liberally throughout an area larger than the patch I will apply
- let the glue dry
- apply no glue to the patch
- peel the foil wrapper off the patch
- apply the patch and press hard
- ensure that the edges have adhered
- don't test it without putting it in the tire.

- don't test it without putting it in the tire.
I understand your reason for this but, if I am patching at home, I'll inflate the tube to 50% larger than it would be in the tire and hang it in the garage for a few days to make sure if it holds air before deflating, rolling and returning to duty.

Honestly, it's usually OK, but it bears a small risk. Just so you know.

You can not patch a hole on the inside of your inner tube.

Actually you can patch a hole on the inside of an inner tube, but the patch will not hold.

I've never heard that repairing a tube on the inner "rim side" was more challenging than repairing it on the outer "tire side."

You learn something new every day.

It is pretty rare that a tyre will resist being patched if you follow the right steps and patching the rim side should not present issues.

I don't get many flats and think the last one was the first in well over 5000 km (on the same bike and tyres)... I carry a spare tube and when I have time will patch the tube which then becomes my spare tube.

I can get tubes here for $3.50 retail (but pay cost) while a patch costs pennies and will provide a permanent repair (glued patches)... I can prep the tube by sanding and pre-gluing and then go do other things and come back to the tube in 5-10 minutes and apply the patch.

The whole process only takes a minute of my time which costs 75 cents.