I had to solder some copper water supply pipes recently. Fortunately, none of the connections leaked. I am using a standard butane (blue) torch.
With most joints, when I touched the solder to the heated metal, the solder was drawn into the joint just as it should be. But on a couple of joints, the melted solder seemed to ball up on the surface of the pipe (though these connection still did not leak).
Why would this happen? -Did I not clean the surface properly? -Did I not apply enough flux? -Did I overheat the joint before applying the solder?
Thanks for your help.