oldgit

i have a brazilian black slate floor in my house its been laid about 3 years.
the floor was hg impregnated but not sealed,i know i should have but it looked great with just the impregnator.
the floor is now looking a bit dull so it needs a deep clean and then seal,what is the best product and the best method of cleaning.
the tiles are flat and un-riven so its only surface grease and grime.
i have tried a small hand held steamer and it seemed to work fine,any opinions on the steamer.
and what is the best long term sealer i have around 100 mts to do in 4 rooms.
time is not really a problem as it is in my own house so 1 room at a time.
thanks