The eco-construction through the Hempcrete

There is a trend in hemp building that is giving plenty to talk about lately. It is the Hempcrete, a material that stands out for being light and resistant at the same time, as well as being exceptional in terms of thermal regulation and humidity. If we add to this that it is sustainable, resistant to fire and that it is classified as a negative carbon, we do not understand why it is not yet being used more in the manufacture of buildings throughout the world.

The truth is that, in some countries in Europe, the hempcrete is a well-known trend, which has been used for decades, as in France, which began in the 90s. Currently, places like the United Kingdom have also been added, The Netherlands or Germany. And it starts giving a lot of hype in North America. What’s more, when we talk about our country, things change. In Spain it is still a very new practice, almost unknown, apart from certain circles where talking about hemp is normal.

Hemp concrete

But what is the hempcrete? This word mixes two English terms: Hemp and concrete. So we could refer to it as hemp concrete. Or what is the same, a biocomposite element that offers many advantages and is made from this vegetable fiber, which serves precisely to isolate and to build.

The secret of the hempcrete is that it is a very resistant material. The cellulose richest hemp fibers, mixed with lime are used for its making and, in the state of limestone powder; In addition to sand and water. After about two minutes stirring, emerges a paste that can be molded to carry out all kinds of construction structures: bricks, walls, foundations … This paste is moldable and can be located in the place in question manually. What is the secret of his extraordinary ambivalence? When time passes, water, lime and hemp petrify, resulting in a light and strong structure at the same time.

A resistant and malleable material

Is the strength of this material immediate? No, as we have explained previously, it is curing with the passage of weeks, months and even years, so it takes some time. For this reason, to avoid curing, there are people who, instead of applying the fresh paste to the wall, choose to buy directly the cured bricks.

The hempcrete can be up to seven times stronger than the materials we normally use for construction and weighs less than half. It is also three times more malleable than concrete. The more time passes, the more petrified, so it becomes more resistant over the years. Everything is advantages!

Like bamboo, which is resistant and flexible, the hempcrete does not lose its ability to malleability by becoming more resistant, so it is all-terrain materials. While a normal building could last hundreds of years, experts in this material estimate that a construction with hempcrete could last thousands of years, since it does not crack with small earthquakes.

A sustainable material

For now, we have seen that it is a malleable and strong material that regulates moisture naturally and prevents unwanted elements such as mold. But hemp is also a very sustainable material for two reasons: first of all, it is a crop that grows very fast and in a renewable way. In second place, it has a zero carbon dioxide footprint, since hemp cellulose absorbs and blocks this colorless gas. According to an article by True Activists, the U.S. Green Building Council, “buildings represent 38% of CO2 emissions in the United States. A great advantage of using hempcrete is that, hemp will absorb CO2 and release oxygen during its growth, in addition to absorbing more CO2 due to the limestone, to petrify then slowly. For decades, its widespread use could have quite a significant impact.”

A lot to offer

Many bet on the hempcrete as a building material of the future, since, in addition to all the virtues previously exposed, it is ecological, sustainable, 100% recyclable and resistant to fire and water. For all these reasons, many professionals in this industry are investigating their possible uses. Knowing all this, it is difficult to understand why is still little known. Or perhaps its invisibility is a direct consequence of the world prohibitionist policy that restricts its cultivation, although, now, it begins to be more permissive in some countries.

• What is it normally used for? As it is a good insulator it is usually a great ally to protect older houses from cold and / or heat. It also serves to lift walls and to isolate ceilings.
• Is it a new material? In no way, since the first remains of hempcrete appear documented on a bridge in France back in the sixth century.

The Hempcrete book: design and construction with hemp-lime

The book by William Stanwix and Alex Sparrow is a very complete document that begins its first chapter putting us in context: what is the history of hemp and the uses it has had; to focus, on the second chapter, in hemp in construction. This publication can be very practical for professionals in architecture, topography and construction.

In addition to including color photographs, it provides explanations of construction techniques and highlights potential hazards and how to avoid them. In the synopsis, we can read:

“Hempcrete is a building material with excellent properties. It is made from lime and hemp leaves (a waste product from the hemp fiber crop) and can be used for walls, floors and roof insulation. Hempcrete is breathable and absorbs and emits humidity; this helps regulate internal humidity, preventing trapped humidity and mold growth, and creating healthier buildings. It provides excellent acoustic and thermal insulation, as well as thermal mass. It is light, it reduces construction costs and it is respectful with the environment: it blocks CO2 during the building’s useful life and hemp does not require agrochemicals or insecticides in its cultivation. The Book of Hempcrete is a valuable tool for any eco-builder”.