When it's fresh, just starting to itch, vinegar poured on it works.
It burns/stings a little then it stops and the poison ivy is not a
problem anymore.
Perhaps the combination helps--we always use vinegar to neutralize the
alkalinity of the cement powder on our skin. My sense of it is that
when the cement powder dries, the weeping is stopped and the itch does
not occur. I did it because it was expedient. It worked. Now, a few
days later, the rash is diminishing. The duration seems shorter.