Corrosion Preventatives

Castrol Rustilo Aqua 21

Castrol Rustilo Aqua 21 Soluble Corrosion Preventive Oil


Castrol Rustilo Aqua 21 (previously called Aquasafe 21) is a medium viscosity, mineral oil-based product containing film-forming additives and coupling agents, which is supplied as a concentrate for dilution with water prior to use. After the evaporation of the water phase, the product leaves an ultra-thin, oily film on ferrous components.


Rustilo Aqua 21 is an inter-operational, short to medium term corrosion preventive which is used as an emulsion. It is particularly recommended for protecting metal components from corrosion after other aqueous treatments. Rustilo Aqua 21 can be applied by immersion and low pressure spray.


Castrol Rustilo Aqua 21 Soluble Corrosion Preventive Oil Advantages:

  • Free from hydrocarbon solvents, complies with EC Solvent Directive (1999/13/EC)
  • Heavy metals free (for example, Barium), which may help to fulfil aspects of legislative requirements and waste treatment requirements that specify that these chemicals are excluded.
  • The emulsion is stable up to 80°C (176 °F)
  • Very good stability against inorganic salts. May be used even after applications where high levels of contamination could be expected, e.g. after heat treatment or electroplating processes
  • Excellent wetting properties
  • Rustilo Aqua 21’s protective film can easily be removed by an alkaline cleaning process
Metal typeCast Iron, High alloy steel / Stainless steel, Low / Med alloy steel
Corrosion protectionIndoor Storage
Formulated without BoronYes
Formulated without Heavy MetalYes
Product typeSurface Treatments
Applicable to these sectorsAerospace, Automotive Manufacture, Machinery, Metal Goods, Metals

User Advice

Always add Rustilo Aqua 21 to water (preferably at 30 – 35 °C (86 – 95 °F)) when making an emulsion. As Rustilo Aqua 21 gives a semi-stable emulsion, it is beneficial to keep the fluid bath in constant circulation, for example with a circulation pump, stirrer or by continuous component throughput. Check concentration, pH and bath level regularly, especially if the emulsion is used hot. The protective film must be completely dry before packaging. In order to minimize the risk of any stability or corrosion issues caused by increasing levels of water hardness and corrosive inorganic salts (i.e. chloride), it is recommended to top up evaporation losses with deionized water.

Additional Information

The claims on film thickness and consumption are average values. These are valid for smooth surfaces with good drain-off characteristics and simple geometries without holes or recesses. “Indoor storage” describes the storage of ferrous components in closed store rooms having a relative humidity of 60%. Full corrosion protection can only be provided when the water is completely evaporated. Increased protection times could be achieved by treating finished surfaces or storing the fully dried parts in a sealed pack.  “Outdoor storage” describes open storage, which assumes primary protection from the elements by tarpaulin or other form of cover.


To avoid product deterioration always keep the container/drum tightly sealed. For optimum product stability, store between 5°C / 41°F and 45°C / 113°F in a cool, dry place away from direct sunlight. Prevent exposure to frost and avoid water ingress. It is preferable to store the product indoors. For more details, please refer to the Safety Data Sheet for this product. This product was previously called Aquasafe 21. The name was changed in 2015.

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Product Data Sheet 

Safety Data Sheet

Castrol Rustilo Aqua 21 Rust Preventative Lubricant Oil

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