Concrete and masonry structures are naturally subjected to moisture during and after the construction phase. This moisture will lead to the deposition of white or greyish-white salt on the surface of the concrete and masonry which is known as efflorescence. This article is about efflorescence, where we will deliver the types, causes and the most important part “how to remove it” from the affected concrete and masonry surface.
What is Efflorescence?
In chemistry, efflorescence is the process where some solid compound loses the water of crystallization when expose to air or a dry environment. This results in the formation of a white powdery substance on the surface of the compound.
Efflorescence is a natural phenomenon of crystalline deposition of salt, usually white or greyish-white, on the surface of masonry, concrete or plaster after evaporation of water. This water moves to the surface carrying dissolved salt through capillary action in the concrete, masonry units, brickwork, and mortar. It often appears just after the completion of the structure within 48 hours.
The salts responsible for efflorescence can come from a variety of sources, including the raw materials used in the masonry, the mortar used to lay the masonry, and groundwater that permeates the masonry. When water carrying these salts evaporates on the surface of the masonry, the salts are left behind and form the characteristic white deposits.
Efflorescence is a surface issue that does not affect the structural integrity of the masonry. However, it can negatively impact the aesthetic appeal of buildings and lead to long-term damage. In severe cases, the salt deposits can absorb water and expand, causing the masonry to deteriorate over time and the surface to flake or spill.
Definition of Efflorescence
As per ACI 116R-25, it is defined as “a deposit of salts, usually white, formed on a surface, the substance having emerged in solution from within either concrete or masonry and subsequently been precipitated by reaction, such as carbonation, or evaporation.“
As per ACI CT-13, it is defined as “ a generally white deposit formed when water-soluble compounds emerge in solution from concrete, masonry, or plaster substrates and precipitate by a reaction such as carbonation or crystallize by evaporation.“
Chemical Compound
The most common salts deposited are calcium carbonate, sodium sulphate and potassium sulphate. During the hydration of concrete, calcium hydroxide ((CaOH)2) is formed which is slightly soluble in water. The compound gets dissolved in water and is carried to the surface, where it reacts with carbon dioxide (CO2) in the air forming calcium carbonate (CaCO3) and water. Water escapes in the form of vapour and leaves insoluble calcium carbonate on the surface. This phenomenon is called efflorescence.
This insoluble salt (CaCO3) cannot be washed with plain water. Thus it requires a weak acid solution or abrasion to wash or clean it from the concrete surface. However, salts formed from potassium or sodium are soluble in water and are easily removed by washing with plain water.
Types of Efflorescence on Salt Content
There are three main types of efflorescence:
Calcium Carbonate Efflorescence:
This type of efflorescence occurs when calcium carbonate is present in a material formed by the hydration of Portland Cement and reacts to form calcium hydroxide. The insoluble calcium carbonate is formed when exposed to moisture and air where water escapes leaving the calcium carbonate efflorescence on the surface.
Calcium Sulphate Efflorescence:
This type of efflorescence occurs when calcium sulphate is present in the material and is exposed to moisture and air. Calcium sulphate efflorescence is formed on the surface after the escape of water.
Silicate Efflorescence:
This efflorescence occurs when alkali silicates in the material react with carbon dioxide in the air to form a white, powdery deposit on the surface.
Types of Efflorescence on Occurrence.
There are generally two types of efflorescence occurrence on the concrete or masonry surface. The occurrence of efflorescence is dependent on the time which is classified as primary and secondary efflorescence.
Primary Efflorescence
Primary efflorescence is a type of efflorescence that occurs when there is excess water used for curing concrete members. This excess water dissolves the soluble salts in the concrete mixture and brings them to the surface of the concrete as the water evaporates. As the water evaporates, it leaves behind a powdery white deposit on the surface of the concrete, which is typically seen within 45-72 hours after excessive curing.
Although primary efflorescence is primarily a cosmetic issue and does not usually affect the structural integrity of the concrete, it can still be unsightly and may require cleaning to restore the appearance of the concrete.
Secondary Efflorescence
Secondary efflorescence is a type of efflorescence that occurs due to an external source of water, such as rain or condensation, that penetrates into the concrete and dissolves the soluble salts present in the concrete mixture. As the water moves through the concrete, it carries the salts with it and deposits them on the surface of the concrete as the water evaporates. This results in a powdery white deposit on the surface of the concrete.
Unlike primary efflorescence, which occurs shortly after the curing process, this type can occur months or even years after the concrete has been installed. This is because secondary efflorescence is typically caused by a change in the surrounding environment, such as increased moisture levels or exposure to water.
Secondary efflorescence is more concerning because it indicates that there may be an issue with the integrity of the concrete. The presence of external water can weaken the concrete and compromise its structural integrity, potentially leading to cracks, spalling, or other forms of damage to masonry units.
Causes of Efflorexcence
Both primary and secondary types occur in the presence of three conditions. If any one of the conditions is removed, it will not occur on the surface of the masonry and concrete materials.
- There must be soluble salt/compounds in the masonry or adjoining materials.
- There must be water available to pick the salt in the solution.
- There must be evaporation or hydrostatic pressure that causes the solution to migrate to the surface.
Factor Affecting Efflorescence
- Moisture: Water is a key factor in the formation of efflorescence. When water penetrates the brickwork, it can dissolve salts within the bricks, which then move to the surface as the water evaporates.
- Salt content: Bricks that have high levels of soluble salts are more prone to efflorescence. These salts can come from the raw materials used in making the bricks, the mortar used to lay them, or from groundwater that permeates the brickwork.
- Temperature: The rate of efflorescence can increase with higher temperatures, as more water evaporates from the surface of the bricks.
- Airflow: Poor ventilation and airflow can cause moisture to become trapped within the brickwork, which can contribute to the formation of efflorescence.
Preventative Measure
Preventative measures such as using high-quality materials, ensuring proper drainage, and applying appropriate sealants to protect against water penetration can help avoid the occurrence of efflorescence. Efflorescence can be prevented by taking certain measures such as:
- Using high-quality materials: Using high-quality masonry materials that are less likely to contain soluble salts can reduce the occurrence of efflorescence.
- Proper drainage: Ensuring that the building has proper drainage systems in place can help prevent water from seeping into the masonry and causing salt deposits to form.
- Applying appropriate sealants: Using appropriate sealants on the masonry can help protect against water penetration and prevent the formation of efflorescence.
- Controlling moisture: Avoiding excessive moisture around the masonry by controlling the humidity levels within the building can help prevent efflorescence.
- Proper cleaning: Regularly cleaning the masonry can remove any existing salt deposits and prevent them from building up over time.
How To Remove Efflorescence
- Dry brushing: A stiff-bristled brush can be used to remove efflorescence from the surface of the masonry. This method should only be used on dry masonry to prevent pushing the salt deposits deeper into the masonry.
- Water washing: Lightly washing the masonry with clean water can help dissolve and remove the salt deposits. However, care should be taken not to saturate the masonry with water, as this can cause the salts to dissolve and penetrate deeper into the masonry.
- Chemical cleaning: Certain acidic cleaning solutions can effectively dissolve and remove efflorescence from masonry. However, these solutions should be used with caution and should not be left on the surface of the masonry for too long, as they can cause damage.
- Sandblasting: In severe cases, sandblasting may be necessary to remove efflorescence. However, this method should only be used as a last resort, as it can cause damage to the surface of the masonry.
FAQs:
Q: Is efflorescence bad?
A: It does not cause any damage to the strength of the concrete, however, it spoils the aesthetic of the finished concrete surface.
Q: Should efflorescence be removed from the concrete?
A: Yes, it should be removed if the building develops efflorescence on its finished painted surface because it makes the building looks awful, old and unwelcoming.
Q: How long would efflorescence occur?
A: It will not be stopped from occurring unless the moisture movement is stopped on the concrete surface. However, as time passes the intensity of salt deposition will decrease.
Q: What is efflorescence?
A: Efflorescence is a crystalline deposit of salts that forms on the surface of porous materials such as concrete, brick, and stone.
Q: How can efflorescence be removed?
A: Efflorescence can be removed by brushing or washing the affected surface with a solution of water and muriatic acid or other commercial efflorescence remover products.
Q: Can efflorescence come back after it’s been removed?
A: Yes, efflorescence can come back after it’s been removed if the underlying moisture issues are not addressed or if the conditions that caused the efflorescence to form in the first place are not corrected.
Also, read:
- What is Bleeding in Concrete?
- Concrete Laitance | Definition | Cause | Remedy
- Types of Bricks Used in Building Construction
References:
- ACI 116R-25. Cement and Concrete Terminology
- Efflorescence. (2015). Methods to control efflorescence in alkali-activated cement-based materials. https://www.sciencedirect.com/topics/chemistry/efflorescence
- Efflorescence. (23, June 2022). Designing Building.https://www.designingbuildings.co.uk/wiki/Efflorescence
- Efflorescence. (12, November 2022). In Wikipedia. https://en.wikipedia.org/wiki/Efflorescence
