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Old 12-28-12, 08:02 PM   #1
mdilthey
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Cyccomute explains patching and repairing your gear- Must read!

I found this post so enlightening and so informative, I had to share this. Thank you cyccomute for answering my question so thoroughly!

Original Thread:http://www.bikeforums.net/showthread...at-Thermarests


"No. It's not 'just glue'. Therein lies the problems that many people have with patching tires. First a quick lesson in materials. Lots of people...including me...are guilty of not really specifying what materials are. A Thermorest pad is not made of polyester. It's made of nylon. Ortlieb bags are polyester that has been coated with polyvinylchloride (PVC). Tubes (and tires) are made of butyl rubber. All three are very different polymers that react in different ways to adhesives. Polyester, for example, is tough to glue. To make stuff out if it you have to melt it (aka weld it) or stitch it together. Not many adhesives really bond to it. PVC is a bit better but still requires special glues. Nylon is easy to stick many adhesives to but not all. Hide glue, for example, doesn't stick to it but isocyanates (superglue) does.

And then there is rubber. You can bond adhesives to it but not very well. It's an elastomer so the adhesive has to stretch with the bond. Not many glues can do that. With rubber you 'weld' a patch in place by making new chemical bonds that make the patch become part of the rubber. The bond then stretches with the patch because it's just like the rubber around it. To accomplish this, you usually use a 2 part system. Each system may not be compatible with other systems. Your Park patch may not work with a Rema patch and vise versa. Rema...with which I am familiar...uses a specific mixture of compounds in the fluid and a specific mixture of compounds coating the patch surface. When these are brought into contact (without solvent interfering), the immediately start a chemical reaction that forms new bonds between the rubber of the patch and the rubber of the tube. If you use Park vulcanizing fluid, it may be missing a component that is necessary to start the reaction and won't make a good bond. If you use 'rubber cement', it will be missing components needed to initiate the reaction and won't bond at all. It will stick but it won't form the bonds needed.

If you were to put the vulcanizing fluid on your nylon pad, the reaction would start between the patch and the fluid but it wouldn't form any kind of bond between the pad and the patch. There's not avenue for a reaction between the nylon and the vulcanizing fluid since they are completely different materials.

Finally, the flexibility issue isn't just limited to rubber. Pads are rolled or folded or generally made smaller somehow for packing. The surface adhesive between the pad and the tape will move during all this manipulation. Eventually the patch is going to come loose...i.e. fail...and have to be reapplied. I'd use the patch from Thermorest rather then just any old tape in case they are doing something to make the bond more flexible and/or permanent. I also go to great lengths to avoid getting holes in my sleeping pad because they can be a bugger to find and fix."

-cyccommute
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