Causes of Efflorescence on Facing Bricks and 5 Methods to Remove It

One of the most important factors affecting the quality and beauty of facing bricks is efflorescence, since facing bricks are widely used on building exteriors. Therefore, understanding the causes of efflorescence and methods of removing it is of great importance.

On Which Types of Bricks Does Efflorescence Occur?

Efflorescence is caused by organic compounds and minerals present in the clay of bricks, which appear after the evaporation of water absorbed in the bricks. Bricks that contain lime in their raw materials are prone to efflorescence. When bricks effloresce, their color may change to yellow, white, green, or brown. This problem not only affects appearance but also impacts durability.

Another cause of efflorescence is cement-mixed water used for brick pointing, which penetrates the bricks and, after evaporation, leaves efflorescence on their surface. Poor-quality mortar used for installing facing bricks can also lead to efflorescence.

Substances That Cause Efflorescence in Bricks

• Potassium sulfate (formed by the reaction of clay bricks and cement)
• Nitrate (originating from mortar water)
• Calcium sulfate (from salts in brick clay)
• Sodium carbonate (from pointing mortar)
• Potassium carbonate (from pointing mortar)
• Calcium hydroxide (from cement)
• Manganese oxide (from the brick itself)
• Iron oxide (caused by contact with iron)

Types of Efflorescence on Bricks

1. Carbonate Efflorescence

When mortar or grout containing lime is used, the carbonates left after evaporation of water cause efflorescence. To prevent this, mortar with little or no lime should be used.

2. Chloride Efflorescence

If hydrochloric acid (muriatic acid) is used to clean carbonate efflorescence, it may react with lime deposits and create calcium chloride efflorescence, which must then be washed with water. If concentrated hydrochloric acid is used, the wall should be completely dry beforehand; otherwise, residues may remain in joints and later appear as efflorescence. Also, if the water used for brickmaking, mortar, or pointing contains high levels of chlorine, chloride efflorescence will occur.

3. Sulfate Efflorescence

If gypsum mortar and sulfate-rich water are used for wall construction, and lime is added to accelerate setting, rainfall may trigger sulfate efflorescence, which continues until all gypsum has converted into efflorescence.

4. Nitrate Efflorescence

Sodium nitrate (Chile saltpeter, NaNO₃) is a white powder or colorless crystal with a sweet odor, highly soluble in water. It absorbs wall moisture and later appears as nitrate efflorescence on the surface. The best way to prevent this is to use purified water in brickmaking.

Methods of Removing Efflorescence from Bricks

Brushing

Efflorescence can be removed with a dry plastic or wire brush. The brush should not be applied too harshly to avoid leaving marks on the brick surface.

Wire brush

Water Jet Cleaning

One of the simplest methods is washing the surface with pressurized water. After cleaning, the wall must be dried properly to prevent water residues from spreading and causing more efflorescence.

Hydrochloric Acid (Muriatic Acid)

A diluted solution (1 part acid to 12 parts water) can be brushed on the wall and then rinsed with chlorine-free water after drying. Incorrect use may cause discoloration of bricks.

Brick Cleaning Solutions

Special brick cleaning solutions can remove mold and efflorescence, leaving the wall clean and shiny. The solution is brushed on and then rinsed after drying.

Sandblasting

Also called abrasive blasting, this method uses fine sand particles propelled with compressed air to clean the wall.

After using any of these methods, applying a nano-brick waterproofing sealer is recommended.

Conclusion

Efflorescence occurs mostly on bricks made from clay with impurities or when water with salts, chlorine, or lime is used in production or mortar. To remove it, methods such as brushing, sandblasting, water jet cleaning, hydrochloric acid solution, or specialized cleaners are used.
Facing bricks fired at higher temperatures, like Azarakhsh refractory bricks, have lower water absorption and therefore show minimal efflorescence compared to ordinary bricks.