Help on plumber's putty!

Posted in Custom Workstation

I've been using Plumber's putty for my sculpting, and so far, it was working great, but now, I accidentally left it out in the open without a cover.
In the morning, it was kinda dried out, so I squirted a little water on it, but then it became too umm... "cement-ty".
Like real cement, wet and gray.
I'm just wondering what happened to it?
Is it ever gonna go back to it's original form, the white clay like substance?