Mining firm claims to produce sustainable building materials from waste . He says that gypsum , `` a relatively common mineral geologically , '' is indeed a great heat insulator and can be very strong -- but only as long as it stays dry . Score: 6 Over 60 houses built so far , each one saving estimated three tons of CO2 , says firm .
Mining firm claims to produce sustainable building materials from waste . Score: 6 Over 60 houses built so far , each one saving estimated three tons of CO2 , says firm .