The cement portion binds with the soil and gives the block its sturdiness. Mixture Design and Selection ISSB Block Strength Soil (parts) Sand (parts) Cement (parts) Soil (organical material) Remarks Mix 1 x20 x1 x2 Mix 2 x6 X1 x4 Mix 3 x5 x1 Looks 20% sturdy Costs . These figures are based on cost and availability in Zambia.