Hempcrete

Hemplime

Hempcrete/hemplime is a bio-composite made of the inner woody core of the hemp plant Cannabis Sativa L. mixed with a lime-based binder. The hemp core or “Shiv” has a high silica content which allows it to bind well with lime. This property is unique to hemp among all natural fibers. The result is a lightweight insulating material ideal for most climates as it combines insulation and thermal mass.

Like other plant products, hemp absorbs CO2 from the atmosphere as it grows. Furthermore the carbonization lime during curing adds up to this effect as lime turns to limestone, a process that may last 100 years. Hempcrete is a renewable, non-toxic and breathable material that produces a comfortable and healthy indoor living environment with high indoor quality. It is a low density material (around 1/7th the weight of concrete) and resistant to crack under movement thus making it highly suitable for use in earthquake prone areas.

The concrete industry is responsible for a large amount of CO2 emissions worldwide. Global CO2 emissions from cement production represent 4.5% of global CO2 releases from fossil-fuel burning. Other disadvantages include phenomena such as surface runoff, the urban heat island effect, generation of concrete dust and emission of toxic and radioactive substances. These hazards only make the need for more ecological and human friendly construction greater.

Hemplime is one of the best performing, non-toxic, ecological and renewable materials available. It has a negative CO2 footprint thus alleviating the Greenhouse effect. It improves air quality, energy consumption for heating and cooling providing a comfortable and healthy living environment. Cool in summer and warm in winter.

Characteristics

•  

  Naturally termite, pest and mould resistant.
• Durable (weather-resistant).
• Solid mass construction giving good air tightness (no heat or cool lost through air gaps).
• Hygroscopic thereby buffering fluctuating temperature and humidity.
• Negative carbon footprint (~100kg of CO2 lockup per cubic meter used).
• Fully recyclable and reusable without huge energy requirements to break it down.

Hempclay

Hempclay is a new insulative building material that consists from of the inner woody core of the hemp plant Cannabis Sativa L. mixed with clay binder. The success of the mixture is based on the purity and quality of clay and hemp hurds.

The natural binders are colloids, of which clay is the most common and oldest in use during the human construction history. Clay is considered to be the material in the soil, smaller than 0.002 mm.
It is sticky and swells when wet, hard and shrinks when dry. Clay particles are in the form of round or polygonal flat discs/plates. They have an electric charge that makes them to operate like magnets. When dry, all the negatively charged sides cling to positively charged sides of another clay disk next to them. The addition of water separates the discs far enough apart to weaken the electric charge. When the water evaporates, the electric charge is re-activated, binding the clay disks back together. Therefore clay is in a constant and reversible state of flux.

Due to the nature of clay, Hempclay is proposed for dry climatic zones or inner walls. Hempclay requires more drying time, but includes less energy production than Hemplime.

Hemplime & Hempclay are the new allies, along with other natural materials like straw, clay, wood and stone, in constructing buildings that last for generation, reinventing the meaning of ‘Eco-Construction’ (Ecodomè in Ancient Greek translates to "House Construction").

Sources-Bibliography:

1. James Henderson: Earth Render -  The Art of Clay Plaster, Renders and Paints
2. Gernot Minke: Earth Construction Handbook - The Building Material Earth in Modern Architecture
3. American Lime Technology
4. Hempcrete Australia PTY LTD. Energy saving eco building
5. NRMCA Publication Number 2PCO2 Concrete CO2 Fact Sheet February 2012
6. Hemp Materials

Natural Building - Light straw-clay

History

For most of our existence on Earth, we have lived without architects, engineers, designers and manufactured building materials. In many societies, almost everyone knew how to make their own tools and homes. They learned from observation, experiments and practice. In Europe, light straw-clay houses are examples of culture development. This technique, also known as a light clay or a light loam, evolved from a heavier clay method called wattle and daub, which has been used in construction for at least 6.000 years (now mostly in use in the preservation of historic buildings)

Due to the lack of building materials after World War II, interest in clay building was intensified and a standard clay building code was introduced. In Europe during the 1970s and 1980s clay products were tested, improved and used with renewed vigor. As a further result, "straw/clay" was developed.

Due to its simplicity, affordability and creative possibilities, we believe there is rising opportunity and fertile grounds to apply light straw clay technique nowadays.

Architecture

Post and beam (also called timber frame) is ideal for building light straw clay walls. Structural frame and the weight of the roof are carried by a wood and it is important to be designed in accordance with the International Building Code. Because the timber frame structure is completely surrounded by the clay and fiber enclosure the frame has timeless protection from environmental factors. Timber structures can be deconstructed and then re-used for many following years.

For building our houses we use Greek pine wood.  10x10 cm beams are placed vertically and horizontally on the stone foundation. The space between columns is 15 cm, which makes exterior walls 35 cm thick. The internal walls are 10 cm thick.

Materials for making light straw clay

The tools and experience necessary to build light clay straw walls are minimal.

Straw - Straw can be wheat, rye, oats, rice or barley, and should be free of visible decay and insects. Availability of straw can fluctuate with the season so it is important to have some knowledge of the local agricultural cycles to access the best selection of material. For our constructions we have chosen wheat straw as it was the most locally available type.

Clay soil - Soil should have a minimum clay content of 50% by volume. Making a clay slip is pretty easy: we place soil in the cement mixer (as it’s easier for bigger quantities) and by slowly adding water, it reaches the right consistency, which is that of a heavy cream.

Light straw clay mixture - We place all straw stems in a big table and pour evenly of clay slurry onto the straw. Everything needs to be mixed well by hands until they are thoroughly and evenly coated so as to avoid pockets of dry straw.

Straw bricks - Light straw clay mixture can be replaced by straw bricks. Our straw bricks are made in a special mold, which allows us to adjust the dimensions by movable partitions.The slip-coated straw is placed into the forms and compacted.

Building the walls

Timber battens - should be fitted horizontally to the structure, in order to "lock in" the straw-clay mass. First we nail battens along the one site of a wall. The next step is to fill the wall with light straw clay mixture. Once each layer is complete we nail horizontal batten, to prevent loss of material from the wall, then we tamp next layer of infill until the wall is complete. The material should be pressed good to fill all corners of the wall. Once the wall has dried for a week, we may need to add more mixture in gaps that appear.

Wall drying time depends on the season and climate (wind and relative humidity). Depending on the straw, there are some of missed seeds sprouting, when they shrivel and die, the wall may be dry enough.

The wall can be checked also by moisture meter, the moisture content of the wallsneeds to go below 18%.

Suggested Reading:

• One Straw Revolution: Light Clay Straw Construction. Jacob Schmidt
• Building without borders. Joseph F. Kennedy
• Natural Building Colloquium.An Introduction to Traditional and Modern German Clay Building. Frank Andresen
• Research Report. Initial Material Characterization of Straw Light Clay. JoshuaThornton 2004