What Is Efflorescence Its Causes Examples and Differences
The migration of a salt to the surface of a porous material, where it forms a coating, is known as efflorescence (which means "to flower out" in French). The most important step entails dissolving an internally held salt in water or, on rare occasions, another solvent. The salt is now kept in solution in the bath, which migrates to the surface and evaporates, leaving a salt coating.
Water is the invader in "primary efflorescence," and the salt was already present internally; "secondary efflorescence," on the other hand, is a phase in which the salt is initially present externally and then brought inside in solution.
Efflorescences can be present in both natural and man-made environments. It can often indicate internal structural weakness (migration/degradation of component materials) on porous construction materials, but it can also present a cosmetic outer issue (primary efflorescence causing staining). As seen in the spalling of brick, efflorescence can clog the pores of porous materials, causing internal water pressure to destroy the materials.
In this article, we will study mineral efflorescence, masonry efflorescence, brick efflorescence, white efflorescence, anti efflorescence and efflorescence treatment in detail.
Efflorescence Treatment
Cleaning the wall with high-pressure water has long been a popular method for removing efflorescence. However, since the salts are water-soluble, there's a chance they'll seep back into the wall and reappear as crystals later. As a result, the first line of protection should be to clean the walls with a stiff brush to eliminate the rest of the white. Water pressure washing can then be used to remove any remaining salt from the walls.
When calcium carbonate or calcium sulphate is the source of efflorescence, it is more difficult to remove. It sticks to the wall very firmly and is difficult to scrape with a brush. In this scenario, an acid-based treatment is recommended.
Masonry Efflorescence
Brick Efflorescence
In efflorescence, magnesium sulphate, calcium sulphate, sodium sulphate and carbonate (and sometimes chloride and nitrates) are commonly found. These salts have been connected to the brick itself, construction sand, base soil, groundwater, construction water, and loose earth left in contact with brickwork. Bricks containing more than 0.05 per cent magnesium sulphate should not be used in building. Sand should have a soluble salt content of less than 0.1 per cent (chloride and sulphate combined).
Efflorescence in Cement
As water percolates into poorly compacted concrete, cracks, or poorly constructed joints, the lime compounds in the concrete leach out, resulting in efflorescence (the formation of salt deposits on the concrete surface). Calcium hydroxide Ca(OH)₂, one of the hydration products that is slightly soluble in water, migrates to the concrete surface through the capillary mechanism, causing this.
The solid Ca (OH)₂ reacts with atmospheric carbon dioxide CO₂ to form calcium carbonate CaCO₃, a white layer on the concrete surface, after evaporation.
Efflorescence on Walls
White marks on internal walls can be caused by efflorescence on plaster, which can occur behind paint and wallpaper.
These white, fluffy salts are "crunchy" to the touch, and the crystals that form underneath wallpaper or paint are strong enough to force these coatings off the plaster, or "pop" the plaster. This type of sulphate crystal formation can occur in any building, regardless of age, where water enters the structure. Evaporation would cause the water to leave the wall, leaving the salts behind. While the salts can be rubbed off, they often reappear and cause more harm to the décor.
Efflorescence Plaster
Efflorescence on plaster surfaces is caused by the presence of salts in lime, cement, sand, bricks, and often even water used in building. The soluble salts dissolved by moisture are drawn to the surface through pores after the plasterwork is completed and fully dry. These soluble salts absorb moisture from the air and store it in patches as a white crystalline material when it dries. The surface is marred by unsightly efflorescence patches. This weakness allows the structure to deteriorate over time. It is usually of a transient type, as it vanishes in rainy weather and reappears in dry weather.
Efflorescence on Stone
Efflorescence will cease in all but the most severe cases as crystallised salts block capillaries in the stone. The white deposits will slowly wear off with use and exposure until the process has stopped. Water and a stiff-bristled (non-metal) brush will always suffice for clients who are in a hurry to get rid of it. The haze will resume if the efflorescing process is not stopped or the factors that cause it are still present, and it will need to be cleaned again.
Examples of Efflorescent Salt
By the process of homogeneous nucleation, a 5 molar concentration aqueous droplet of NaCl can spontaneously crystallise at 45 per cent relative humidity (298 K) to form a NaCl cube. The initial water is freed into the gaseous state.
Gypsum (CaSO₄.2H₂O) is a hydrate solid that will give up its water to the gas phase and form anhydrite in a sufficiently dry environment (CaSO₄).
When exposed to sunlight, copper(II) sulphate (bluestone) (CaSO₄.5H₂O) is a blue crystalline solid that steadily loses water of crystallisation from its surface, resulting in a white layer of anhydrous copper(II) sulphate.
When exposed to sunlight, sodium carbonate decahydrate (Na₂CO₃.10H₂O) can lose water.
Did You Know?
Three key factors contribute to the formation of efflorescence on concrete and brick masonry walls. The following are the conditions:
Soluble salts could be present in concrete and brick masonry walls, and the salts could be found in masonry brick, mortar, adjacent dirt, and backing material.
Water must be present in the concrete and brick masonry walls, and it must come into contact with soluble salt in order to dissolve it.
The pore structure of concrete and brick masonry walls must allow soluble salt to migrate to the surface, where water can evaporate and leave the salt.
FAQs on Efflorescence in Chemistry Explained
1. What is efflorescence in chemistry?
Efflorescence is the process by which a hydrated salt loses its water of crystallization when exposed to air, forming a powdery solid. It occurs because the salt is unstable at room temperature and releases water molecules to the surroundings.
- Common in hydrated salts.
- Results in loss of mass due to removal of water.
- Often changes the appearance from crystalline to powdery.
- Example: Na2CO3·10H2O(s) → Na2CO3(s) + 10H2O(g)
2. Why does efflorescence occur in hydrated salts?
Efflorescence occurs because some hydrated salts are thermodynamically unstable at room temperature and lose their water of crystallization to the atmosphere. When the surrounding air has low humidity, the equilibrium shifts toward water loss.
- Weak attraction between salt and water molecules.
- Low atmospheric humidity accelerates the process.
- Surface exposure increases the rate of dehydration.
3. What are some common examples of efflorescent substances?
Common efflorescent substances include hydrated salts that easily lose water when exposed to air. Typical examples are:
- Washing soda – Na2CO3·10H2O
- Glauber’s salt – Na2SO4·10H2O
- Epsom salt – MgSO4·7H2O (slowly efflorescent)
- Ferrous sulfate – FeSO4·7H2O
These compounds gradually become powdery as they lose water molecules.
4. What is the difference between efflorescence and deliquescence?
Efflorescence is the loss of water from a hydrated salt to the air, whereas deliquescence is the absorption of moisture from air until the substance dissolves. The two processes are opposite in nature.
- Efflorescence: hydrated solid → anhydrous solid + water vapor.
- Deliquescence: solid + water vapor → aqueous solution.
- Example (efflorescence): Na2CO3·10H2O.
- Example (deliquescence): CaCl2(s).
5. What is water of crystallization?
Water of crystallization is the fixed number of water molecules chemically bound within the crystal structure of a hydrated salt. These water molecules are essential for maintaining the crystal’s shape and stability.
- Represented in formulas using a dot (·).
- Example: CuSO4·5H2O contains 5 water molecules per formula unit.
- Removal of this water changes physical properties.
6. How can you prevent efflorescence in laboratory chemicals?
Efflorescence can be prevented by storing hydrated salts in airtight containers and controlling humidity. Minimizing exposure to dry air reduces water loss.
- Use sealed glass bottles or desiccators.
- Store in a humid environment if necessary.
- Avoid prolonged exposure to open air.
7. Is efflorescence a physical or chemical change?
Efflorescence is primarily a physical change because only water molecules are lost without altering the chemical composition of the salt. The anhydrous salt formed remains chemically the same compound.
- No new substance is formed.
- The process is often reversible by adding water.
- Example: CuSO4(s) + 5H2O(l) → CuSO4·5H2O(s).
8. How does humidity affect efflorescence?
Low humidity increases the rate of efflorescence, while high humidity slows or prevents it. The process depends on the equilibrium between the hydrated salt and water vapor in the air.
- Dry air favors dehydration.
- Moist air may maintain hydration.
- Critical humidity varies for each salt.
9. What happens to the mass of a salt during efflorescence?
The mass of a salt decreases during efflorescence because it loses water of crystallization to the atmosphere. The loss in mass corresponds to the number of water molecules released.
- Example: Na2CO3·10H2O loses 10 moles of H2O per mole of salt.
- Mass loss can be calculated using molar masses.
- This principle is used in gravimetric analysis.
10. Can efflorescence be reversed?
Yes, efflorescence can often be reversed by adding water to reform the hydrated salt. The anhydrous salt reabsorbs water under suitable conditions.
- Example: CuSO4(s) + 5H2O(l) → CuSO4·5H2O(s).
- The blue color of hydrated copper(II) sulfate reappears.
- Reversibility depends on environmental conditions.
