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You are here | Home | Tech/Blog | Technical Information | Efflorescence​ 

EFFLORESCENCE

1.  What is efflorescence?

Efflorescence in concrete is seen as a white powder deposition of salts on the surface of concrete. It occurs with all concrete and is the most frequent problem faced when dealing with concrete, plasters, and mortars.
Efflorescence is caused when soluble salts and other water dispersible materials come to the surface of concrete. It is induced by low temperatures, moist conditions, condensation, rain, dew, and water added to the surface of fresh concrete to assist trowelling.
2. What causes efflorescence? ​
​
  1. The presence of salts in one of the materials of concrete. Commonly found in the fine aggregates or sand taken from riverbeds.
  2. When concrete is not cured properly.
  3. Slow rate of evaporation of water allowing time for salts to permeate to the surface.
  4. If the water content in the concrete mix is high, it makes the concrete porous. Thus, allowing the path for water and salts to come to the surface, causing efflorescence. This is most likely to happen in rainy, cold seasons.
  5. Underlying moisture issues prior to laying concrete, screeds, or overlays.
  6. Using too much water in the mix and finishing process.
3. How can efflorescence be prevented? ​
​
  1. A well graded concrete mix with a water reducer to minimize paste.
  2. Use of concrete ingredients such as aggregate, cement and sand which contains a smaller quantity of salts.
  3. Application of sealers and coatings can prevent surface water from penetrating slabs. Apply them as soon as the surface is clean and dry.
  4. Ensuring there is no underlying moisture issues prior to laying concrete, screeds, or overlays.
  5. Not using too much water in the mix and finishing processes.
4. How do I treat efflorescence? 
​
The easiest time to remove calcium hydroxide efflorescence is before it combines with the carbon dioxide in the air. Up to this point it will dissolve in water, so pressure washing, or wet scrubbing will put it in solution with water so it can be rinsed away.
Before you can remove efflorescence from a surface the cause of the issue needs to be identified. If there is an underlying issue such as a leaking water pipe or a slab with no damp proof membrane (dpm) this will need to be addressed first; if not, the efflorescence will keep reoccurring.
There are a few ways to try and mitigate the visual impact of efflorescence, such as washing with water or a diluted acid wash solution and brushing the surface. However, be aware of the following precautions:
  • Washing with water:
Using a pressurized water jet can help to dissolve the efflorescence quickly but care needs to be taken. If the floor is new and not yet hard a pressure washer may damage the surface. Be sure the surface can handle the treatment. A soft broom with clean water may suffice at early stages to remove the efflorescence. Be sure to remove the contaminated water with a vacuum; if this is left on the surface to dry on the surface, the efflorescence may return. It is essential to wash the entire surface and not just the affected area, so as to unify the drying of the surface, which affects the final finish and colour. If this step doesn’t work an acid wash may be required.
  • Diluted acid wash solution:
Concentrated pool acid (hydrochloric) is not recommended to use on concrete. A diluted proportion of 1 part acid to 10 parts water (1:10) is good to use. The surface will need to be pre-dampened before the solution can be applied. Once you have pre-dampened the surface you will apply the solution and allow it to react for about 10 – 15 minutes. Then a soft bristled broom can be used to gently scrub the surface. Remove all the acid solution with a wet vacuum. Thereafter you will neutralize the surface using a diluted mixture of bicarbonate of soda and water (1:5) to ensure that all the acid is thoroughly washed off. Again, it is essential to acid wash the entire floor and not just the affected area, so as to unify the drying and hence the final finish and colour. There will be slight colour loss with this method.

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