Aquamix makes very good products that may help in your circumstance. They're sold at better tile shops or you can contact the company for instructions and tips. Here's a link that may help you out.
http://www.aquamix.com/for_home_use/...asp?sfid=35733
Since Mexican tiles are porous and not glazed they are softer and more subjected to scratching than glazed tiles. You may find it hard to totally eliminate the problem.