What Causes Efflorescence and How do You Remove it?

efflorescence-slab-brick-blockWhat Causes Efflorescence

So what causes efflorescence? This is when soluble salts and other water dispersible materials come to the surface of concrete and mortars. Low temperatures, moist conditions, condensation, rain, dew, and water added to the surface of fresh concrete to assist troweling and curing help promote efflorescence. It can occur very soon after exposure to moist or cool conditions or gradually Especially when it comes from within the concrete or from water entering from outside or moist soil.

Basically what causes efflorescence relates to the chemical structure of the concrete. The chemistry of cement plus water containing carbon dioxide results in the formation of efflorescence.  The reaction of carbon dioxide and water to forms the weak acid (carbonic acid). This reacts forming insoluble Calcium salts = efflorescence. Insoluble salts formed within the wall, tend to blocking further ingress of water (presence of stronger acid will dissolve the efflorescence). Effectively drying out the wall over time.

What Causes Efflorescence and How do You Remove Efflorescence?


Removal of Efflorescence and salts from masonry

First pressure wash to remove the hardened lumps. This traditionally followed by 10% hydrochloric acid in water applied by brush or low pressure spray. Then washed off by hose.

Moisture in any material containing Portland cement results in efflorescence. The reaction occurs when calcium hydroxide (lime) formed in the hydration reaction of Portland cement. Around 60 Kilograms per cubic yard of concrete is transported by water to the surface through capillaries in the concrete. There it combines with carbon dioxide from the air to produce calcium carbonate (an insoluble material) and water. Efflorescence is also caused by hydroxides and sulfates of either sodium or potassium. These salts are much more soluble in water than calcium. And they form efflorescence more rapidly than calcium hydroxide. These salts can come from cement, aggregates, water, or admixtures.

Efflorescence is normally white and shows up more on darker colors than white or light grey because of the contrast. Producing six (6) grams of calcium carbonate per square metre causes a significant shift in colour. Some forms are very difficult (if not impossible) to remove. While others are easy. Especially if they are removed right after they form.

What Causes Efflorescence and How do You Remove Efflorescence?

Chemistry of Efflorescence

Portland cement clinker is a hydraulic material that shall consist of at least two-thirds by mass of calcium silicates, (3 CaO·SiO2, and 2 CaO·SiO2),

Calcium oxide that survives processing, without reacting, in building products such as cement are called free lime.

Calcium hydroxide (traditionally called slaked lime) is an inorganic compound with the chemical formula Ca(OH)2. It is a colorless crystalline white powder. Calcium oxide (called lime or quicklime) forms when mixed, or slaked with water.

CaO + H2O →  Ca(OH)2 → Ca2+ + 2 OH

After the formation of the Calcium Hydroxide  (Ca(OH)2)  the water is being absorbed in the concrete, masonry, and brick contains carbon dioxide reacts with the water to produce carbonic acid (H2CO3)

Ca(OH)2 + CO2 → CaCO3 + H2O

Most salts formed in moist, damp and wet concrete are relatively insoluble. Evaporation dries the salts leaving them on the surface of the masonry.

Prevention of Efflorescence what causes efflorescence

Suffice to say preventing or minimizing efflorescence, the elimination of the presence of water or not allowing the surface to retain moisture. Design, detailing and construction practices that promote resistance to water penetration are the most effective methods of preventing efflorescence.

  1. Treating the concrete to prevent mold or weed growth
  2. Sealing any cracks which have appeared
  3. waterproofing the surface

Preparation by removal with Efflorescence-Rid will resist the reformation of the efflorescence. This allows better results when using any sealing method.

  1. Coatings like paint are water resistant.
  2. Use of Sealtight Clear or Ultra Masonry Block Sealer provides saturation of the masonry repelling or stopping effective penetration by water.
  3. Fully waterproof cementitious materials such as the Maxseal Waterproof coating completely prevent water penetrating the surface. The Maxseal also traps the moisture in the wall. Any efflorescence (insoluble salts) formed by this moisture is locked in the structure. This causes the drying inside the wall.

  • Now you know what causes efflorescence. Scheduled regular maintenance of concrete surfaces. Thus avoiding what causes efflorescence.
  • In doing so we avoid the need to treat the efflorescence.

concrete crack repairs needed- waterpenetration cause more damage

The presence of mould and weed growth helps keep moisture on the surface longer creating further damage to the masonry surface. As already stated this is what causes efflorescence in the first place. Causing even more efflorescence.