Three parts white vinegar one part distilled water
Three drops of oil of cloves and 2 teaspoons of bicarb soda and a squeeze of lemon. Stir and separate batches so you can have one clean batch to finalise job.
Heavy Duty – not so chemical free:
Tile hydrochloric cleaner:
I used a solution blend of 3 parts warm water, I part hydrochloric acid (from pool shops) small amount of laundry powder or powder for auto dishwasher.
The caustic nature bleaches the stain out let sit for 10 min then refresh and scrub with very stiff broom. Finish with plenty of fresh water to flush the solution of the surface dry with old beach towel.