JeffOYB

Yeah, it's an old one. And I see lots of hits for it in Google. But I just tried it and it didn't work.

What's the scoop?

OK, I've also complicated things a couple ways.

First, I'm trying to patch in a new valve. I cut out the old, leaving a 1" hole. I have a new one to patch in with 1" all around, giving at least a 1/2" overlap everywhere.

(Why am I doing this? For a third crazy reason. I have an irreplaceable Tufo cross sewup. I rolled it and tore off the valve. They're known to be tubeless. I open it up and it has a nice, regular tube. Stuck to the casing, but it readily peeled up. I have the section exposed and want to at least try splicing in a new valve. THEN I'll try sewing this tire shut. I'll lay in a section of thin fabric first. Yeah, funny, I know.)

Anyway, I glued it all up then glued it. It all laid in smoothly. After a day, it peeled up easily. I didn't sand the tubes. Also I neglected the talc angle. The tubes seem dry and clean and not talc'y, but who knows. So I used thinner and alcohol to clean off the old glue and sanded both surfaces good. Everything looked clean and spotless and dry.

I reglued. And let both surfaces dry for an hour. I reinstalled the patch. I clamped it for a day. Then I let it cure further for another day.

Today I tried to put a little air in to test. It held a bit but when the tube got a bit more of a bulge to it, it blew a half-inch gap.

I've now reglued and reclamped to see if I can get that section to hold.

I used Park patchkit glue the first time. I'm now using car-tire vulcanizing cement from auto parts store. (I use enough of this stuff that I finally bought some in bulk.)

Any hope for using a tube to patch a tube?

Is there an issue here of hole size? (Jobst talks about patches failing from the lip of the hole outward.)

Andrew R Stewart 

I've used tube pieces as patches, although never tried to patch in an entire valve. The tube piece gets the same prep as a tube would when using a typical patch. Roughen up the piece, apply glue, let dry. I might have applied a second layer of glue, don't remember. The tube gets the usual prep then the ready tube piece is placed onto the tube.

I did this years ago as a challenge from a coworker. The result ws an air tight job but a clunky/lumpy patch. Andy.

bud16415

That’s a tall order but I can see why you might be trying it. I have as a kid without patches $$$ and nothing but time used tube material to patch tubes. I was about 10 and my dad taught me how to patch a tube and the process was nothing like what was rolled up in the can on the directions. For what it’s worth dad way was to smear the contact glue on both parts and light it with a match. We watched it to look glossy black about a few seconds on fire and you blow it out and slam the patch or tube material on and roll it with the can. If you try a hot patch experiment with an old tube a few times first. You might have to put a piece inside or something so you wouldn’t bond it to the other side.

As my dad walked away after my lesson he said “And try not burning the shed down.”

Bill Kapaun

One of the main problems in patching failures in general is not cleaning the surface of the rubber well enough.
You have to be nearly brutal in cleaning off all old, oxidized rubber. Just because it "looks" clean doesn't mean it's clean enough.

JTGraphics

This is were I get most of my supplies from and you will find many use full other products for your projects also.
https://www.gemplers.com/tires-supplies

Spoonrobot 

There's a difference between tubular and tubeless, which you just discovered. Those tires are tubular tyres: https://en.wikipedia.org/wiki/Tubular_tyre

AlphaDogg

You misinterpreted what the OP meant. His tubular lacks a traditional tube like most tubulars have. It's just a thin rubber coating on the inside of the tire with a valve stuck in. OP: can't you just peel this up and stick in a regular latex tube?

gyozadude

The problem you're having is stretch. When you apply the patch, the tube is relaxed, unstretched. When you inflate it, especially around the valve, the tube expands and put a LOT of stretch that will form shear. Unless you get perfect bond and adhesion with no gaps and the two surfaces are truly vulcanized together, any gap that allows air to get from inside to the outside just works eventually to spread the patch from the tube, and it doesn't take much to allow all the air to come out.

This isn't a big problem with small pricks on the tube. But a 1 inch diameter hole is "big" to say the least. You may do better as someone suggested above and replace the tube and just sew it back up. But what a sewing chore. Good luck.

wroomwroomoops

It does work just fine, as long as you clean both surfaces with ethanol or isopropanol.

wroomwroomoops

+1

JeffOYB

I messed up at first perhaps by not cleaning. But then I used thinner to remove all old glue then sanded and scrubbed with rubbing alcohol. Any chance the thinner was a problem and maybe didn't get all removed? Is thinner ruinous to cement?

wroomwroomoops

The scrubbing with alcohol should have taken care of the (aliphatic, I imagine) thinner. Note that the two aren't really miscible (alcohols and aliphatic compounds), so the best thing is to just let it evaporate and then try the patching.
Note that both surfaces must be clean.

zebede

Rubbing alcohol contains glycerine (a lubricant), I would not use it as a cleaner for patch prep. I would use the ones recommended above. I have used acetone recently (because I had some) it also seems to work well. Don't know about paint thinner.

wroomwroomoops

Are you 100% sure about this? In Finland, it does certainly not contain any glycerine. It does contain denaturants, but they are all volatile solvents.

AlphaDogg

Alcohol is alcohol. Some rubbing alcohol does have glycerine, but it is advertised to contain glycerine. I buy only 90% alcohol (the other 10% is just water).

JeffOYB

OK, one half of my big patch seemed to stick. The other half has been giving me problems. I keep swabbing Vulcanizing Cement over both surfaces and letting them totally dry, or dry to tacky, or not dry, then I either pinch shut or I clamp shut and give it a day to set up. But the one half keeps leaking and the patch isn't sticking so hot. So I just pulled off the whole patch. The bad half was fairly easy to pull off. The good half was stuck on pretty good and seemed to hold air.

OK, I want to make a fresh start on this patch. Is there a good way to re-clean both surfaces? There's old glue residue on both. How to clean that off?

Then I'll want to reglue. Is there one best way? It kinda seems like various experts each have a different method. (Dry, tacky, wet. Clamp or pinch.) Or at least the people who post here do. I dunno if they're experts. I'm trying to give myself best odds here. Cure times?

Thanks.

wroomwroomoops

Tacky, definitely tacky. Honestly though, I never thought about the "level of dryiness" too much. It never gave me any issues, as long as it wasn't fluid.

If the vulcanizing glue sticks really well onto the rubber, you could just as well leave it there (unless it forms thick clumps). Whatever you do, try your best to keep grease off the surfaces involved.

If you use rubbing alcohol for cleaning, make sure yours is not that odd brand with glycerin AlhpaDogg has at home. Cheap denaturated alcohol works great.

Finally, make sure you apply at least a bit of heat while you press the surfaces together. I found that my body temperature is more than enough. If you are a vampire or a lizard, use a blow-drier or such.

AlphaDogg

I don't have rubbing alcohol with glycerine, I just mentioned that I've seen it in stores.

cyccommute 

Corrections:

Alcohols can dissolve in aliphatic mixtures like mineral spirits. The amount that dissolves is dependent on the alcohol used but even methanol...the most polar of the alcohols...has a high solubility in mineral spirits. Probably greater than 15% and likely closer to 50%.

Whatever is in 'rubbing alcohol' depends on the brand. I don't know of too many that have glycerine but I have seen it in the past. My wife has run across them when she didn't read the label.

Okay, I'm going full geek on you AlphaDogg because an alcohol isn't just an alcohol. Alcohol is a homologous series of compounds that have the general formula of CnH2n+1OH. The hydroxyl (OH) functional group is what makes the alcohol an alcohol. The names of the alcohols are derived from their aliphatic group names and the number of carbon atoms in that aliphatic chain. They can extend from 1 carbon atom to an infinite number of carbon atoms and can be saturated (having only single carbon-to-carbon bonds), unsaturated, cyclic, branched or have constituents that are not alcohols branched from the chain. They can even have multiple OH units hanging off the carbon skeleton. These are called polyols.

The more common alcohols we consumers run across are methanol, ethanol (drinking alcohol), isopropanol (rubbing alcohol), erythritol (Stevia sweetener), xylitol (a sugar alcohol used in gum and tooth paste), ethylene glycol (antifreeze) and even glycerine. There are, literally, millions of alcohols with many, many uses.

The main part of your problem is that you are using the wrong tools. Vulcanizing fluid is one part of a two part system. The vulcanizing fluid contains a promoter that accelerates the vulcanizing process but the patch contains the chemicals to actually do the chemistry forming the bonds to the rubber. Essentially, you are using a poor rubber cement to try to make the bond. And the formulations are specific to the product. Rema products are made so that the two parts work together. If you use a different glue, you won't get the same result.

Rema makes a valve replacement kit but it's not for a bicycle valve. Perhaps you could take a large patch and use a hole punch to create a hole for the valve. Leave some rubber around the valve and carefully glue the valve to the center of the patch while avoiding contamination of the rest of the patch so that the whole thing looks like the picture in the link. Then glue the rest of the patch to the tube. You may want to practice on some other tubes before you try the final product.

DannoXYZ 

Yes, the patch has uncured rubber and sulfur. That's the other half of the mixture needed to create vulcanized cross-linked bonds between layers of rubber. JeffOYB, try two tests with the exact same procedure. Start by sanding & cleaning off two 1.25" circles on a tube:

1. over one circle, apply a regular red patch using vulcanizing fluid
2. over the 2nd circle, apply a cut-up patch made from tube using the same vulcanizing fluid (clean that patch really well with sanding like the area on the tube)

Press on both for about 30-seconds after applying. Wait a day or two and peel them off. You'll find that the cut-up tube patch will come off. The actual patch+vulcanizing fluid combo will be bonded so permanently, that you'll end up ripping the patch and/or the tube when trying to separate them.

FMB42

Are you using a latex tube to make the patch from? If so, you might try doing so (according to J Brandt "patching-in" a tubular valve stem (with a latex replacement) has evidently been successful in the past. You might also consider extending the size of the latex patch-in beyond the previous "failed" patch area (if your initial latex re-patch attempt fails). Note: this may not work because of size of the hole you're working with.

wroomwroomoops

On Monday I am going to visit the physical chemistry lab and do the experiment with methanol and decane. That way I'll use the empiric method to prove you wrong.



The vulcanizing glue I use, always vulcanizes even when I use simple pieces of tube as patches. I assume that this happens because there is always a small but appreciable amount of sulfur in the tube rubber.