Sodium Sulphate (Anhydrous Na2SO4) is commonly referred to as salt cake. Sodium Sulphate reacts with cement hydration products such as calcium hydroxide to form calcium sulphate. The calcium sulphate reacts with aluminates having an expansive effect on cement. Improved cement bonding is one of the benefits of using Sodium Sulphate in cement slurries. Typical treating rates range up to 10% by weight of cement.
Sodium Sulphate is used as a drilling mud additive to assist in hole stability while drilling through evaporite beds and stringers such as anhydrite. The Sodium Sulphate reduces the anhydrite solubility, thus reducing the hole enlargement through the evaporate.