The counter is poured in two sections. The first half (4") is normal concrete, I actually used high strength concrete mix, in which the reinforcing bars (rebar) are embedded. The top layer is a mix of cement and vermiculite. The latter is a mineral derived from mica which holds heat, The recommended mix is 3 parts vermiculite to 1 part cement. I used this mix for the edges of the counter top, but in the middle added more vermiculite to closer to a 4:1 mixture, for more heat mass. All concrete and cement was mixed by hand!
