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  • Jorgen Hempel

HempLime or HempCrete

Updated: Jul 14, 2021


Definition of Natural Materials: materials derived from nature; they have undergone a very minimum amount of processing or modification; they contain no synthetic additives nor toxic elements; and the materials are globally beneficial to nature, human health and comfort.

HempLime or HempCrete?

Although many people entering hemp construction are familiar with the term HempCrete, we feel it is important to understand the difference between HempCrete and HempLime. HempCrete is closely associated to concrete because the binder used to produce HempCrete, is cement.

Many people that hear the word HempCrete initially think of concrete with hemp thrown in. That is definitely not the case as HempLime is completely different to concrete and therefore we are using fresh terminology for this revolotionary building material. If we're going as far as to change the building materials industry from synthetic to natural, we may as well change the terminology...

We've evolved from the use of cement and use only the purest form of hydrated lime.

A HES-mix HempLime wall with a bee visitor

A HempLime wall (using HES-mix) with a bee visitor

Hemp as a Construction Material

When HEMP HURDS (the wooden part of the stem, where the fibers have been removed) are used as a thermal and humidity regulator, we have in our hands a natural material that cannot burn or rot due to its high content of silica.

HEMP HURDS require a binder to become a useful building and renovation product.

When choosing the type of binder it is important to assure not to annul the natural benefits of the hemp, by choosing a synthetic or cement binder.

The following binders would qualify to make this assurance:

  • 90-98% pure hydrated lime (first choice)

  • Natural hydraulic limes (NHL)

What is Hydrated lime ?

Calcium Carbonate or limestone that we find in nature, world-wide, it is heated at 800-900°C over a period of time, during this time CO2 is released from the calcium carbonate (CaCO3) to make Calcium oxide (CaO), a lightweight stone. Just the right quantity of water (H2O) is added to hydrate the CaO (a process known as lime slaking) which then causes the stone to react violently and crumble apart, turning into powder. This powder can either be bagged as hydrated lime or calcium hydroxide (CaOH2) or it can be slaked with more water and turned into what is known as lime putty. Lime putty can be stored forever as long as it is covered with water. There are stories which date back thousands of years where masons would slake lime for their first born son and store it in baths, under their houses, so that the son could one day use it to build a house of his own (hydrated lime does not set under water and will only start carbonating once water evaporates and CO2 is absorbed).

The hydrated lime powder is what we use to make HempLime with and once it comes into contact with water and water starts evaporating and CO2 starts being absorbed, the lime starts 'Carbonating' which is a natural chemical/physical reaction created by nature itself. When carbonating, it takes up a quantity of CO2, and this reaction goes on as long as there is a small quantity of moisture present in the air.

This reaction also causes the Hydrated lime to continue its curing, and will slowly turn back to limestone, becoming stone-hard, possibly petrification or similar. The process is know as the Lime Cycle and is a truly phenomenal characteristic of hydrated lime. Hydrated lime is abundant and available in many parts of the world and has now become, so called, 'air lime' and has a profile completely different from Hydraulic lime.

Hydrated lime was used by the Romans and up through the ages as a unique building material.

The limestone which has too many impurities or argyles to be used for the production of hydrated lime goes into making Hydraulic lime which is heated to 1200 degrees celcius. Hydraulic lime is like cement in that it sets under water. The even more impure limestone is then heated to 1800 degree C and used to make portland cement.

The drawback of Hydrated lime is that it cures very slowly and since this is not in-line with today’s requirement for speed, it has since the industrialization of building materials beginning in the early 1900's, lost its use as a building material and has been substituted with cement to produce concrete.

In Search of a Solution

"In my opinion, the unique qualities of Hydrated lime are too valuable to be lost. With a proven lifespan of 1000s of years, as we see with ancient buildings, and now, the sudden importance of CO2 and its damaging effect on nature and human health."

In 2012, after researching historic literature, a small number of natural minerals were found. It was proven that the effect of a small quantity of these minerals in the Hydrated lime made the latter cure in a couple of days, without losing the uptake of CO2.

Thus a major discovery was made which makes it possible to benefit from what has been known and used for thousands of years. Building houses that will last for hundreds of years, adding the benefit of CO2 uptake which only recently has become of major importance.

What is HES-plus?

Our blend of natural minerals we call HES-plus allows us to use Hemp and Hydrated Lime to make HES-mix (our tried and tested, patented HempLime formula) and use it in the following applications where the indoor climate is of utmost importance:

  • Construction of thermally and humidity regulating walls

  • Insulation of existing walls.

  • Roof insulation

  • Floor insulation

Our products have gone through the various European tests for thermal conductivity, fire resistance, vapour permeability, strength tests and were tested in Treviso, Italy in 2015 showing how 3cm of Hemp and Lime was able to reduce the CO2 content in schools by 35%.

To read the report, click here

Please browse our website to find out more about our systems and products.

Thank you for reading

Jorgen Hempel



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