top of page
  • Jorgen Hempel


The lime Cycle

Much confusion exists around what lime is and what is not. To quote one of the most notorious experts on lime, the Dane, Ole Storgaard said "there is only one type of lime, HYDRATED LIME(CaCO3) also referred to as air lime. That is pure lime at 95-98% purity. Other limes on the market should not be allowed to be called lime." With that categorical statement we will start the story on Lime.

Deposits of Lime can be found in most parts of the world and always in abundance. In certain areas like in Scandinavia the deposits can measure 20 km or more. These deposits date some from 4 000 to 200 million years ago. When sea water evaporated liquid salts are extracted, the first contains lime CaCO3, which is remains of micro particles which through millions of years have been deposited layer after layer on the sea bottom.

Hydrated lime has been used in construction for thousands of years. It hardens by uptake of Co2, where after some water is liberated, known in building as moisture. The lime stone if having a purity of 95% it is heated at 840-900°C till it becomes red hot, turning into Calcium Oxide. Co2 is liberated from the lime stone and through dry slaking (adding small quantities of water), the lime is turned into powder. This lime can now be humidified and will carbonate, namely take up CO2. Hydrated lime is known for its porosity and weaker properties in construction.

If the lime is impure, which means containing more than 10-15% impurities such as argyles, it is slightly hydraulic; with 33% argyles it will become hydraulic and in these cases it will not be able to carbonate.

Due to the impurities in the lime, it needs to be heated to 1100°C to get a slight hydraulic lime; 1400°C for a hydraulic lime and 1600°C for Portland cement. Due to the material’s inability to carbonate and because of it hardness and impermeability, it is cement and not lime. Whereas hydraulic lime has its advantages in rapid hardening and strength, it differs greatly from Hydrated lime where we find a weaker finish a material that is diffusion-open and in particular its ability to carbonate.

hydrated lime powder


PURE LIME: Less than 6% impurities which can be argyles, aluminum and magnesium oxides

SLIGHT HYDRAULIC LIME: 5-10% hydraulic components. Can carbonate slightly

MODERATE HYDRAULIC LIME: 20-25% hydraulic components and more than 60% calcium and magnesium oxides. Cannot carbonate.

NATURAL CEMENT : 45-50% Hydraulic components. 45-50 % hydraulic components, calcium and magnesium oxides. Cannot carbonate.

A number of misleading names are used for the Hydraulic type materials, like white lime, pure lime, and quick lime.

Since we are not building bridges or highways, but living and working quarters for people, the use of hydraulic lime would be catastrophic for old buildings because of its strength and lack of diffusion properties which will clash with any material based on natural materials.

When advocating “the values of the breathing house”, we can distinguish immediately between the two materials. Also in HES-mix and HES-wall the diffusion, the transmission and foremost the carbonation and consequently the up-take of CO2 are the qualities in a building material we are looking for.

That we have been able to improve the hardening of hydrated lime without losing the CO2 up-take is where we have to distinguish ourselves.

Jorgen Hempel

April 26, 2019

Onnens, Switzerland

175 views0 comments
bottom of page