Heard a drywall guy on a podcast say the fast-set stuff has a different crystal structure when it cures, makes it denser than the regular mud. That would explain why the sponge barely dents it. He said the trick is to hit it with the knife while it's still green, like right when it stops feeling tacky, and you can shave most of the ridges off before it fully hardens. Waiting even 20 minutes past that point is what turns it into sanding concrete.

Wait, a 6 AM email? That's wild.

Used to chase fancy coffee spots. Dave changed that.