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Puncture Repair On Seam - May be A Daft Question

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Puncture Repair On Seam - May be A Daft Question

Old 04-24-19, 04:02 PM
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Witterings
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Puncture Repair On Seam - May be A Daft Question

Apologies if the answer's obvious .... but if you don't know / haven't been taught it's not obvious at all .... several times I've watch Who Wants To Be A Millionaire and known the answer to the £125 or £250k question because it's a subject you're familiar with but could have been floored on the £1k question and never would have got there because you didn't have a clue.

I've always considered the "Seam" on an inner tube as a weak spot and also assumed the sanding paper was to rough the area up so the glue has something to take to but I saw a comment a few days back that said if the patch straddles the seam to sand it flat .... Is this correct???

I totally get the concept it creates a raised area that it's easy for air to find a channel to escape down and once as a kid tried re-patching the same place many, many times before I finally gave up and bought a new inner tube but I've always been scared to sand the seam as I've considered it a weakening area.

I'm also asking as I'm doing more and more mileage and about to do my 1st mini tour but don't want to end up carrying multiple spare tubes because I haven't learnt the art of puncture repair properly.

Again .. apologies if the answer is obvious but just interested to have some clarity so I know for the future.
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Old 04-24-19, 04:16 PM
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The seam isn't a weak spot. It's just a result of the molding process. The mold is made of multiple pieces and liquid rubber is poured in, a small amount of rubber leaks into the joins in the mould. Once set the mold comes apart to release the tube and the leaked rubber is left standing proud of the tube surface..
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Old 04-24-19, 05:26 PM
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I'll have to answer the $64 question as I don't deal in pounds sterling. Don't worry about the seam. You don't even need to sand it flat as the patch is flexible enough to mold over the small ridge. I never bother to use the sandpaper or rasp that comes with the patch kits. It's better to clean the area around the hole with a Q-tip soaked in a solvent such as paint thinner or nail polish remover. It will not hurt the tube. It leaves the tube much cleaner than attacking it with sandpaper so you get a better bond with the patch.
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Old 04-24-19, 05:48 PM
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Originally Posted by VegasTriker View Post
I'll have to answer the $64 question as I don't deal in pounds sterling. Don't worry about the seam. You don't even need to sand it flat as the patch is flexible enough to mold over the small ridge. I never bother to use the sandpaper or rasp that comes with the patch kits. It's better to clean the area around the hole with a Q-tip soaked in a solvent such as paint thinner or nail polish remover. It will not hurt the tube. It leaves the tube much cleaner than attacking it with sandpaper so you get a better bond with the patch.

That'd be the £49.61 question at today's rate of 1.29 doesn't quite work like that does it

I get that solvent / cleaner is better ... I'd use isopropyl alcohol at home after I'd rubbed it down as I've always thought that whilst sanding it creates something for the glue to wick into the flip side is it creates a load of dust which isn't attached to anything and is detremental to the glue / surfaces mating so best to clean it .... but don't carry it in the field so use a smidge of water to get rid of "the debris" and wipe dry before applying a patch.

Get what you're saying about the patch should mould around it but I did have the one I mentioned that really wasn't going to seal ... I think I tried 5 times before I gave up and we always cycled through woods and were constantly getting punctures so was very familiar with repairing them ... probably more so then than in my older years.

Might be that occasion was the anomaly as the hole was so close to the seam but maybe sanding it down might have made the difference in that one off situation.

Last edited by Witterings; 04-25-19 at 02:20 AM.
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Old 04-24-19, 09:18 PM
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Originally Posted by Trevtassie View Post
The seam isn't a weak spot. It's just a result of the molding process. The mold is made of multiple pieces and liquid rubber is poured in, a small amount of rubber leaks into the joins in the mould. Once set the mold comes apart to release the tube and the leaked rubber is left standing proud of the tube surface..
This is true. It's flash, a print from the surface of the mold's joins. However, due to the science of the process, it does actually affect the structure of the rubber all the way through to the inner surface. And an inner tube can split along these 'seams' as a result..

That said, i treat it like it's purely outer surface inconsistency, and simply sand off the flash with the sand paper whilst prepping the area, so there's no notable groove in the glue between patch and tube.
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Old 04-25-19, 01:43 PM
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Isn't the patch itself going to reinforce any potential weak spot there?
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Old 04-25-19, 03:16 PM
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I remember a suggestion from some years back that one could use a disposable razor to trim the flashing off an inner tube seam near a hole that needed patching. I tried it a couple times; it worked the first time, and the second time I cut a new hole in the tube. The tube it worked on, though, that was its second or third patch, and the fix held up for nearly ten more patches before I gave up on the tube!
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Old 04-25-19, 05:39 PM
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Originally Posted by BlazingPedals View Post
Isn't the patch itself going to reinforce any potential weak spot there?

This is actually a very good point and something hadn't thought about .. someone who definitely thinks outside of the box ... Engineer???

I think possibly this coupled with the right sandpaper concentrated on the seam and avoiding hitting either side too much is probably the way to go.

Cheers to everyone for their input / help .. always \ appreciated
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Old 04-25-19, 05:50 PM
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Originally Posted by VegasTriker View Post
I'll have to answer the $64 question as I don't deal in pounds sterling. Don't worry about the seam. You don't even need to sand it flat as the patch is flexible enough to mold over the small ridge. I never bother to use the sandpaper or rasp that comes with the patch kits. It's better to clean the area around the hole with a Q-tip soaked in a solvent such as paint thinner or nail polish remover. It will not hurt the tube. It leaves the tube much cleaner than attacking it with sandpaper so you get a better bond with the patch.
I'll go out on a limb and propose it's easier to keep a 1" square piece of sandpaper in your saddlebag than a bottle of paint thinner and some qtips.
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Old 04-25-19, 09:23 PM
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Originally Posted by Sy Reene View Post
I'll go out on a limb and propose it's easier to keep a 1" square piece of sandpaper in your saddlebag than a bottle of paint thinner and some qtips.
Well, yes, but a couple of alcohol swabs belong in every seat bag. You can find them in any drugstore in America, along with the other diabetic supplies. I've got some from a decade ago that are as fresh as new, though the sealed packets are somewhat soiled.
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Old 04-26-19, 05:57 AM
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Originally Posted by Trevtassie View Post
The seam isn't a weak spot. It's just a result of the molding process. The mold is made of multiple pieces and liquid rubber is poured in, a small amount of rubber leaks into the joins in the mould. Once set the mold comes apart to release the tube and the leaked rubber is left standing proud of the tube surface..
Not quite correct. Tubes are not molded, they are extruded as a long tube. The ends are joined and then the raw sticky rubber tube is vulcanized. This last process is where those lines develop.
of the process. Tubes start at 7:37.

To the OP: I have found that if you use a quality patching system like Rema, you won't have many failed patches. Don't worry about any flashing marks, just sand lightly and get on with the patching
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Old 04-26-19, 06:37 AM
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A single edge razor blade with a hook burnished edge works good to remove flashing. How to make one: Rasor Blade Scraping
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Old 04-28-19, 04:42 PM
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Originally Posted by Sy Reene View Post
I'll go out on a limb and propose it's easier to keep a 1" square piece of sandpaper in your saddlebag than a bottle of paint thinner and some qtips.
LOL!! Exactly, it is far easier to simply use a small 1" square piece of sandpaper, and it takes up next to nothing in space in your bag.

There is also no need to take a razor blade and cut down the seam, this is just crazy talk. Any patch will hold right over the seam. And when you sand the tube all you're doing is removing the shine off the area of the tube where the patch will be, don't have to sand it down into the rubber, just take the shine, or sheen off.
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Old 04-28-19, 09:43 PM
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As a recycler -or some would say cheapskate - I hate tossing still good tubes. I've used tubes with 10 + patches on them, so I applied 100's of patches, some of them at the seams. No problem at all.
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Old 04-28-19, 11:11 PM
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Originally Posted by Moe Zhoost View Post
To the OP: I have found that if you use a quality patching system like Rema, you won't have many failed patches. Don't worry about any flashing marks, just sand lightly and get on with the patching
Exactly my experience. I do find it easier to do it at home than along the road, mainly because I use a screen spline tool to to really get the patch set/feathered on the edges.

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Old 04-29-19, 09:21 PM
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Originally Posted by Reynolds View Post
As a recycler -or some would say cheapskate - I hate tossing still good tubes. I've used tubes with 10 + patches on them, so I applied 100's of patches, some of them at the seams. No problem at all.
You're not alone, I do the same thing, I keep patching till the tube is no good usually due to valve stem failure, on a rare occasion either a puncture into a patch, or one on the back of the valve stem, and seams don't matter.
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Old 04-30-19, 12:22 PM
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Originally Posted by scott967 View Post
Exactly my experience. I do find it easier to do it at home than along the road, mainly because I use a screen spline tool to to really get the patch set/feathered on the edges.

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Screen spline tool is ideal, but you can also roll a screwdriver handle tip over the patch to press it good.
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Old 04-30-19, 12:26 PM
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Life is too short to waste time patching tubes.
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Old 05-23-19, 02:35 AM
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Funny I posted this thread a couple of weeks ago .... I was out at the weekend and had a nail go through both sides of my tube with both puncture holes near the seam. I didn't have any sandpaper with me but patched it with skabs (the "jagged" piece of metal included in the skabs packet was fine for roughing up the area but no good for smoothing it off) and continued the ride doing another 30+ miles and it was fine ... the next morning it was totally flat.

I pulled the tube out and the patch had bunched up either side of the seam creating "channels" the air was escaping down, I managed to get the skab off, sanded it down and used a conventional patch / glue and it's been fine since.

Not surprisingly I'll now carry a small patch of sandpaper with me as well
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Old 05-23-19, 11:32 PM
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I just rub the tube on the concrete if I can remove it from the wheel easily. Kerbstones and brick walls are good.
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