After determining the maximum height of the stairs based on the project board dimensions, I established the height of the foundation, which turned out to be four inches. Using inch-thick styrofoam, I cut and glued it to the bottom of the second base kit.
I decided on more rubble and salvage from the 1906 San Francisco earthquake, and was pleased to also repurpose some foundation stones from an abandoned early build. I used the recommended Foamtastic glue, which I’m pretty sure is just an extra-thick tacky, and as a result my thumb joint is sore from *squeezing* the bottle all day.
Here’s the upside-down completed foundation, with a first coat of paint drying, an entire two-ounce bottle of Delta Ceramcoat “Mudstone”. (I’ve since added a wash of “Espresso” to good effect, but lost the light and will have to wait until tomorrow to show you.)