Thermal mass (or thermal inertia) means the capacity of a material to prevent the passage of warmth, storing some of it, while keeping the temperature of internal spaces homogeneous, constant and comfortable, in spite of big variations in outdoor temperature.
This principle is a matter of application of materials, in this case bricks for the load-bearing walls, natural stone for the floors, wood for the ceiling beams and most of the custom furnishings (also salvaged from the few pines that had to be felled to make room for the houses), and local earth from the excavations.
The brick walls have been treated with a sort of veiled stucco created with this earth: “We experimented with more red, less red, trying different quantities of cement,” Barroso says, and the resulting mix has been applied to the walls by hand, obtaining a soft, irregular texture for both the interiors and the exterior surfaces.