HG grout cleaner deep cleans and degreases grout joints. Yellow or brown dirt that is left behind after cleaning is lime scale . This can be removed with HG professional limescale remover (hagesan blue). Use HG mould spray for black deposits on grout. Dilute HG grout cleaner with luke warm water. Then apply with a scrubbing brush or a hand brush. Allow a few minutes for the product to work , scrub well and rinse off with water. One litre is enough for a surface area of 10 to 15 m2.