Seeing your post reminded me I have the same problem and needed to sort it sometime (one of those things you just forget about). I don't think it's going to weaken your line any, unless it opens up and the line starts hingeing on that point, wearing the braided core.
Looking for a soloution I found this post:
fly line repair
That's the heat tratment method covered. I'd like to see someone do a repair like this before I get a box of matches out. Sounds like a good idea.
Chemical option:
Re-plasticisers work by softening up the pvc coating - which will re-seal small cracks etc. It may repair your problem is you apply some into the cut itself.
Phthalates are the most common plasticisers, and are not pleasant. They are being fazed out in the US and EU.
Generally anything making pvc less stable (to liquify it in essence) will release more phthalates and other chemicals, some of which may make your voice and octave higher... OK, I made that last bit up, but they do have cumulative effects in the body - including changing hormone levels! So not nice stuff to play with if you can avoid it really.
I'm going to buy a new fly line from Pitsford Pirate, and then get the box of matches out and see what I can do with just some
mild heat I think. I stress mild - don't want to burn PVC - that also releases some very nasty toxins!
Fly line help
Is there anything I can do to prevent this becoming a weakness in the line?
Linear Mode
