Obviously, it is better not to stain slabs in the first place, but if staining occurs then there are several solutions. Ideally the stain should be removed as soon as possible by extensive flushing and scrubbing of the affected area. If this is not possible to remove immediately, then physical abrasion or a mild brick cleaning acid may be required to remove. These can sometimes do more harm than good to the slab as they may have to be excessively strong to remove the stain and hence a small trial area is recommended. In general, the longer the stain is left before treatment, the harder it will be to remove.