HOW do I maintain my cremeof marfil exterior courtyard floor and how do I seal it? How can I make it more slip resistant when wet?
Dear Joy:
First off, you never seal a polished marble floor. It is actually technically impossible to seal it, because, due to the natural density of the stone (marble is very dense, contrary to popular misconception) teamed with its high surface tension consequent to the polishing, no impegnator (a.k.a. sealer) will ever stand a chance to get absorbed by the stone. (Sealers for stone are strictly below-surface products and must be absorbed by the stone to go there - below the surface, that is.)
Second, you never seal stone outdoors - even stones that could be sealed.
Stone needs to "breathe" to endure and the consequent slow down of the osmosis due to the presence of the impregnator may create irreversible problems.
Third (or first, maybe), Crema Marfil is not the right type of marble to be installed outdoors on grade, unless you provided to put a water-proofing membrane between the subfloor and the setting material. And even so it is not the right stone for outdoors. Without mentioning the consequences of the natural acidity of the rain, if you lose even a little grout, you will be in a world of hurt... :-(
Af for the reduction of the slipperiness, there are special treatments to make the surface of the marble dull and rough through a strong acid bathing. I don't have any link that I could offer you about that, though (it's probably because I really don't like the principle...); but if you inquire with the merchants who sold the tiles to you they should know.