Here's what it looked like shortly after finishing, after Lisa handed over the tools for me to clean.
Today, it appears to have hardened well. It will take some days before it completely dries. Lisa's plan is to eventually fence off this area under the stairs and use it to store propane bottles and other flammable items so she doesn't have to keep them in the garage/workshop.
Now we hope to put this knowledge to work on the main project, about which more when it's done because I don't want to jinx it.