Calcite a bacterial bio-sealant is used to seal cracks and holes in buildings and monuments. We have attempted to enhance the production and application of bio-sealant from Bacillus sphaericus with concrete cubes using mix design for the target compressive strength of 50 MPa by response surface methodology. The optimized media was further optimized for pH and nickel concentrations. The column designed for calcite production was packed with mixture of fine Norris sand, fly ash, urea, CaCl2: and the immobilized bacterial species B. sphaericus. After 7 days of a production cycle, the flyash mixture containing CaCO3 was applied to artificially induced cracked cubes. The cubes were investigated for the variation in their compressive strength at 50 MPa and concluded that compressive strength of calcite applied cubes showed increase in strength compared with cement mortar application. The strength was further enhanced to 37.5% by adding 20% of carbon nano tubes to the total sealant. (c) 2012 Elsevier Ltd. All rights reserved.