Travertine Repair How Do I Clean Travertine?

How do I clean travertine? - travertine repair

I installed travertine tiles and I had no time to seal it. Now its 6 months later, and I think it needs a thorough cleaning before sealing. Some tables have also cracked. I went with cement? What is my best approach? I read with a machine polished travertine is not sure it's the best thing for me.