so i was being stupid and my vacuum sucked up a string that was for LST . It snaped off a side branch at the main stem and scraped a good 6 inches of the outer layer of the main stem. The inside of what ever is under that skin is now exposed.. will it heal fine? Do I need to keep it out of light? it still is supporting the rest of plant but i dont want to it to lead to other problems - bugs/mold. as for the the side stem that totally snaped off, i tryed to place it back and tape it up and am supporting its weight, but its not looking good, a lot of dropping, i dont know if it will make it though the night. there is already a lot of weight on that stem to id stay an 8th now and if not double that by the time it would have been ready. did i mention im 4 weeks into flower - its a sativa looking at 5 more weeks till ready.
Since you're in flower I highly doubt it will grow back together like it would if it were vegging. So I say get rid of the broken branch and put a lightly damp papertowel over the wound and mist it with ph'd water to keep it lightly damp. It should heal quickly.
I've used tree limb paint to protect my citrus trees from infection when I prune it or a branch breaks. The stuff is basically aerosol tar. I don't know if it would be a very good idea to use on cannabis. It might make your bud taste nasty.
try to make it fit just like it did before water it good then tie it and tape.. I broke my main stem in half during LST tieing and i just waterd and tapped the shit out of it liek a bandaid and its still fine. about 4 weeksinto flowering. GL man.