if you are looking for a strong mix then I would advise a 3/1 ratio (3 sand 1 cement) standard mix 7/2 ratio or super strong mix 5/2 ratio a strong mix would normally be for a free standing smaller and single skin outbuilding a standard mix would be for a double skin build (a house) and a super mix would be for a single skin wall no higher than 1.5 metres. hope this helps