Patch fail by getting stuck to inside of tyre

[hubner]

Has anyone got a flat tyre because the patch got stuck to the inside of the tyre?



I got a flat after not riding the bike for a couple of days. I seem to get hardly any actual punctures these days but instead get leaking patches, or the tube has a tiny split just through age and wear and tear.

As I took the tube out, one patch on it was stuck to the tyre quite firmly. The edge of the patch was still stuck quite well to the tube but the centre had become completely unstuck and was smooth and slippery, and a silvery white colour.

[Biggsy]

I have patches sticking to the tyre, but they just peel off the tyre cleanly while staying fully adhered to the tube.  Chalk or talc doesn't last, by the way.

It's important to patch properly in the fiirst place.  My top two tips are:  1. The rubber solution should be almost dry, or completely dry, before applying the patch.  2. Do not test the repair by inflating before the tube is fitted in the tyre.

[Brucey]

I think the main problem is that the patch lifted from the tube rather than that it stuck to the tyre. 

The 'silvery colour' beneath the lifted patch is probably talc from within the tube (tubes often have talc inside them). When all the air in the tyre rushes out via the failed patch, it carries talc with it, and lots of talc ends up under the patch, showing clearly which parts of the patch lifted.

Looking at your repair I'd have to say that there is little evidence of

a) enough abrasion prior to applying the rubber solution or
b) enough rubber solution over a wide enough area and
c) that the patch lifted where  (and how) it did is because you stuck it on upside down!!!!

Normally the part of the tube beyond the patch will show signs of having been (weakly) stuck to the tyre, because it too will have been covered in rubber solution.

My tips are that

a) don't stint on the prep (abrasion)
b) two coats of rubber solution, letting them each dry completely before the next thing
c) if you are in a rush you can flash the solvent out of the rubber solution by applying a naked flame to the tube. Don't let the rubber solution burn for more than about one second. Repeat as necessary until the rubber solution is dry.
d) apply the patch (orange side against the tube!).

Even with the best prep, procedure and materials, the bond won't be as strong as the tube itself. Whilst the bond will strengthen over time, it ought to be good enough for immediate use, provided the tube isn't too stretched when it is installed in the tyre and inflated.

If you have a pinprick puncture, it makes sense to inflate the tube (to about the size it will be when installed) after step c) and then apply the patch.  This will ensure that the patch isn't being strained when the tube is installed.

If you are working at the roadside you have little choice about what materials you use etc (you will only have what you brought) but if you are working at home you can take your time and use different materials that are not practical to carry around with you. For example tyres often transfer mould release compound onto the surface of (otherwise clean) inner tubes and this will inhibit adhesion.  At home a good first step is to use a solvent to clean the tube. Cigarette lighter fluid (pound shop) is very good for this purpose. Meths is OK too.

cheers

[hubner]

Looking at your repair I'd have to say that there is little evidence of

a) enough abrasion prior to applying the rubber solution or
b) enough rubber solution over a wide enough area and
c) that the patch lifted where  (and how) it did is because you stuck it on upside down!!!!

I always spend quite a lot of time roughing up the tube but it's possible I didn't for this repair but I think it's unlikely. The perimeter of the patch was stuck quite well, it was actually quite hard to pick off the bits left on the tube. The photo shows the underside of the patch, which is also now also silvery white and completely non-sticky. I'm certain it wasn't stuck on upside down!

My theory is that movement of the tube inside the tyre had caused the tube under the patch to loosen because the patch was fixed in position in relation to the tyre but the rest of the tube was free to move around just tiny bit. Once the centre of the patch had loosened, the patch stayed stuck around the perimeter and this held but eventually gave way at one spot enough for air to esacpe.

Or it was a faulty patch that didn't have glue in the middle!

[Biggsy]

The only thing I know that can seperate a well-applied conventional patch from a tube is heat - sausage-burning amounts of heat.  So unless that happened I don't believe the middle of the patch was ever fully bonded, regardless of whatever the tyre did.

[Brucey]

there is a line in the tube that is still visible in the prepared area; this hints that tube maybe wasn't abraded enough.  I guess the patch just looks as if it was on upside down; sorry about that!

 I agree with Biggsy BTW, I don't think the middle of the patch was ever properly bonded.

However, to clear up a misunderstanding; patches don't have 'glue' on them.  The orange layer is unvulcanised rubber; it has many sites within its molecular structure that are free for bonding (this rubber will in fact react and harden all by itself over time) and it is also slightly porous. The black layer is a vulcanised layer; it is stronger and more airtight; without it the repair wouldn't be robust enough and it would also (gradually) leak air.

The tube normally moves inside the tyre as it is inflated and then stays put subsequently.  Only gross deformations of the tyre will then produce further movement; for example tyres that have been run nearly flat are usually obvious, because there is lots of evidence that the tube has been moving. The relative movement generates lots of scuffing on the outside of the tube and lots of little bits of rubber debris are generated. Your repair shows no signs of such relative movement.

If the patch isn't bonded well enough it will always lift first where the hole is. However if it is adhered very well at the edges, all round, this is usually a pretty good sign that the rubber solution wasn't  dry enough when the patch was applied. I think what happens is that the remaining solvent is able to diffuse away (through the orange layer) at the edges of the patch but not in the centre, so the edge of the patch may stick to the tube (and to the tyre perhaps) but the bond isn't necessarily any good elsewhere.

cheers
 

[Ham]

I always leave the plastic film on the back of the patches to minimise the chances of this happening

[Brucey]

I always leave the plastic film on the back of the patches to minimise the chances of this happening

the other thing this does is it alters the way the patch is strained vs the tube when the tube is stretched.  Normally if a patch starts to come away from a strained tube, it will lift in the centre first. However with the backing still in place, I think it sees more strain at the edges instead.

cheers

[mrcharly-YHT]

I always leave the plastic film on the back of the patches to minimise the chances of this happening

Ditto

[Kim]

I always leave the plastic film on the back of the patches to minimise the chances of this happening

I leave it on because peeling it off (even if done carefully, starting from the middle) puts needless stress on the edges of the patch.  It usually comes away next time I remove the tyre.

[hellymedic]

Brucey's patching technique is similar to mine. In addition, I recommend:

Shaving off any protruding seams and 'flashing' (I use an old Bic razor) prior to puncture repair to give the patch a nice flat 'bed' on which to stick.

If forced to patch a tube when it's raining, shelter your work with the peak of headgear and warm the tube from behind with fingertips kept warm by retaining your track mitts.

Don't think I've had a patch stick to the outer tyre for a VERY long time and it's never lifted the patch. I used to decant unwanted smelly talcum powder into film canisters.

Tubes are best repaired in a warm, well-lit kitchen, with copious supplies of TEA & BISCUITS, encouraging an unhurried approach and fully dried rubber solution.

[Biggsy]

I find cotton tyre casing is particular prone to sticking to bare inner tubes, let alone to any patches on them.  Talc/chalk only prevents it for a short while.  It's not a problem anyway.  There's even a theory that it's good (in some way that I can't remember).

[hubner]

I got a puncture today on the other wheel! A small bit of glass on wet roads.

As I took the tube out, I think at least one patch already on the tube had stuck to the inside of the tyre, I peel it off from the tyre and the patch didn't come off the tube. Also I don't think I've had a patch come off after being stuck to the inside of the tyre before. So maybe the patch in my first post wasn't stuck on properly.

[P Walsh]

I only use the patches that need "glue", not the self-adhesive sort. And when I put the patch on I peel it from the foil but leave the transparent plastic film on it as a barrier between it and the tyre.

[Samuel D]

I find cotton tyre casing is particular prone to sticking to bare inner tubes, let alone to any patches on them.  Talc/chalk only prevents it for a short while.  It's not a problem anyway.  There's even a theory that it's good (in some way that I can't remember).

The theory I heard is that it slows the escape of air in the event of a puncture, allowing you to bring the bicycle to a controlled stop.

Hubner: does that large triangular shape in the centre of the patch-site mark the hole in the tube? If so, that’s an unusually large hole that may generate large separating forces. The patch must have separated before you removed the tube from the tyre, since a large amount of talc has made its way between tube and patch.

[hubner]

The hole is actually a very small cut and hard to see; sometimes I cut out the top edges of the cut so I can see where it is.

[Samuel D]

Hmm. While convenient for the reason you state, the cut-out area will probably not adhere or not adhere well to the patch, thereby allowing air at 100 PSI to inflate that cavity and continuously worry at the edges of the vulcanised area. This may have been a contributing factor to this patch failure.

[hubner]

I've just found another patch where the perimeter edges is well stuck but the centre has become completely unstuck. And the tube is silvery white under the unstuck patch. This time the patch hasn't stuck to the inside of the tyre.

The patch was holding but had stretched in the centre so it's not flat (off the bike with no air).

[Brucey]

I hardly dare to ask this...... but did you stick it on the right way up?

cheers

[hubner]

It would be quite hard to, as the foil always comes off when you peel the patch not the plastic film.

And even if the  plastic film peeled off first, it would be obvious it's upside down after you've stuck it on the tube because you can't break the foil by pinching the patch.

[Brucey]

I have seen duff patches where the wrong layer peeled off in preference, but this is rare...

I reckon there are two main differences between the bond at the edge of the patch and the bond in the centre

a) the bond in the centre potentially sees higher strains because the patch is stiffer there (whereas the feathered edge is stretchier) and
b) the potential for any residual solvent from the rubber solution to diffuse  away from the patch centre is less than at the edge; the edge is made of thin, not very cross-linked rubber, through which diffusion is more likely to occur.

The patch anyway sees more stress if the tube is undersize vs the cover, or the patch is near the tyre bead (which strains the tube horribly).

So it is possible that the rubber solution wasn't 100% dry when you put the patch on and this has resulted in a weakened bond in the patch centre more than at the edges.  Modern rubber solution has a higher boiling point solvent in it than the TriCh that was used years ago.   Particularly when it is cool and/or humid, it can take a long while for the  modern solvent to flash off when applying the rubber solution.

 To hasten this process I usually (at home) / often (at the roadside) use a naked flame to drive the solvent off.  If you let the solvent burn for more than about one second there is a real danger that the inner tube will have a (much bigger) new hole in it....... ; you need to be ready to blow the solvent flame out almost immediately, and repeat (after a few seconds to allow cooling) until the rubber solution won't catch light any more.   Just then, the rubber solution is as dry, as moisture free, and as warm as it is likely to ever be before you apply a patch to it, which significantly increases the chances of getting a good bond.

You will know if you have slightly overdone it because the rubber solution will boil and blister if it is too thick, too wet, or is heated too much.

cheers