Originally Posted by
bulgie
I think I heard somewhere that the flux from the rod doesn't soak off in water, or not well. (Also true of some generic paste or powder flux like you'd get at the local welding shop.) I gather you're expected to hammer it off? Thinwall bike tubes don't like that treatment very much.
Yes, some fluxes don't dissolve easily. Really hot water and a wire brush can get most of it off; what remains is usually glass-like blobs. I've used a file with simple downward pressure on the blob to make it shatter and fall off, but it can get tedious. That's what I like about the Gasflux Type B paste: besides being a very effective flux, it comes off easily with hot water and a brush.