A dense off-white chalky deposit can appear on concrete, primarily on grey concrete and on concrete to which colour was added. This is called effloressence.
What is free lime?
Mixing water, sand, gravel, and cement, creates concrete. A product from this mixture is calcium hydroxide. Effloressence is calcium carbonate formed by a reaction between the calcium hydroxide and the carbon dioxide (CO²) in the atmosphere.
In the process of concrete making, the calcium carbonate is the only substance that is not bound to another substance. Once the concrete is in contact with the atmosphere, a chain reaction may start. Calcium moves to the outside of the concrete and binds with the CO² in the atmosphere. This causes Effloressence.
Removing calcium carbonate from concrete surfaces is hard. Under the influence of CO², though, a different substance emerges that is more easily removable. Effloressence may eventually disappear by itself. However, such a process is long and arduous.
Counter effloressence in an efficient way, on both fresh and coloured concrete.
Countering free lime on freshly poured concrete is possible by using Moxilon 200 nano Hydro / Colour. This product comes in colour, but can also be transparent. It has to be applied one day after the formwork has been taken. After the treatment, damp might still come out from the concrete, but moist will not be able to penetrate because of the hydrophobic properties. This process counters effloressence.
When effloressence has already formed on the product, it can be removed by lightly sanding the concrete surface. The removal can be done by using a special wall sanding machine, such as Flex Giraffe, or something similar to perforated sandpaper K100. (Ventilate well!).
After this process, clean the concrete using Decaps Remover Eco Guard and clean water. After drying, the colour layer can be applied.