Extreme conditions !
The outer earth coverings undergo extreme conditions. Considering the frost, the snow, the sun, the rain, you needa reliable solution which resists at best in time. The stone floor of outside is the ideal solution.
Today there are two types of installation in the choice :
The installation in the glue on concrete slab or on screed in the mortar (sealed, traditional method)
The installation on fine gravel or on adjustable blocks, method non sealed, more and more used today