Plasticisers, or water-reducing admixtures, are added to increase the workability of a mix, thus enabling easier placing and compaction. Where increased workability is not required, water reducers may be used to lower the water/cement ratio, giving typically a 15% increase in strength and better durability. The plasticisers, which are usually lignosulphonates or hydroxylated polymers, act by dispersing the cement grains. Some air entrainment may occur with the ligno – sulphonates, causing a 6% reduction in crushing strength for every 1% of air entrained.