The Mexican tile on our back porch is displaying a green growth at the corners of the porch. The porch is outdoors, but is covered. What is this growth and how do I clean it off?

The green growth you see is probably algae. Algae usually grows were there is abundant moisture. My guess would be that the tile stays wet after a rainstorm, allowing the algae to grow. To clean it, prepare a solution of bleach and water; about one cup of bleach to a gallon of water should do the trick. Scrub the tile with this solution and rinse thoroughly. To prevent the algae from returning, it is advisable to seal the tile. Visit your local janitorial supplier and ask for a sealer that can be used outside. Be careful on this point, as many sealers are not recommended for exterior applications.