When I built my super-insulated home in 1984, my plan was to have a walkout basement with a finished concrete slab that would absorb the sunlight from four south-facing windows and act as a thermal mass. I placed a 4-inch slab over a 3-inch layer of sand and 6 inches of XPS insulation, and used an integral red dye in the concrete. In addition, I used a wax-sealing product made by the dye manufacturer that was supposed to match the slab's color and allow the concrete surface to be buffed to a high shine.I'm not sure what went wrong, but...

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