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.
Article ID: 584
Created: January 21, 2022
Last Updated: January 21, 2022
Author: Pam Freitag
Online URL: https://sr-manual.com/kb/article/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-584.html