BioWash is recommended for use to clean light to moderate mold, mildew and biological soiling on all kinds of substrates, including grout and tile. It will not kill the biological soiling, but is made to clean it. How effective it will be on the grout can be judged after doing a test area. Prosoco distributors can get free samples of the product for testing purposes. The one thing about this product is that it can take up to 2 weeks before you see the final results.