As it turned out the slate cleaned up real nice. The sealer gave the stone a nice briliance and made it look real good. It was clear that cleaning the floor will be much easier for the client.
BUT - I decided to re-colour the grout line as the soils and grease has penetrated to groutlines so deep and the marks were still vissible after the clean.
The grout re-colour worked like magic. After the colour cured I applied several coats of sealer to the floor.
