Learn more about Hempcrete

What is Hempcrete?

Hempcrete is a bio-composite material made up of the inner woody core of the Industrial Hemp plant, known as “Hurd” or “Shiv” and formulated hydraulic lime binders.

Industrial Hemp Hurd contains a type of silica that is unique to any other plant in the world. The silica is highly absorbent to the hydraulic lime, making it unique in its practice.

When the two ingredients are mixed with water, a chemical reaction petrifies the hemp while the lime converts to calcium carbonate, known as limestone, using the hemp hurd as an aggregate.

The result is a light weight, self-insulating wall material. Although not structural, it has a mass density of 320kg/m3 when dry. This allows for great thermal mass and the feel of a masonry wall, that is plant based.

The insulation properties are outstanding due to the porosity of the material, the hemp shiv also has capillaries, which are microns of air pockets, captured in the wall that allows a breathability or “hygroscopic” performance. Essentially the material is absorbing humidity and regulates the internal air quality to a medium 18-23 degrees Celsius all year round.

As the material is curing, it is absorbing CO2, with the life cycle of the industrial hemp plant, there is a high amount of carbon capture. It is calculated that a 100m2 home can capture about 20 tonnes of carbon.

As the world looks towards a more sustainable future, the carbon reduction that Hempcrete achieves is the leading building material to provide the opportunity for buildings to be carbon neutral, or even better, carbon negative.

The Hempcrete is a form of limestone, which cannot catch fire. The material is rated to BAL FZ (flame zone) compliance which is valued at 60/60/60 minutes of penetration to minutes of fire breach.

Other benefits of hempcrete are:

  • Termite resistant

  • Pest resistant

  • Mould resistant

  • Non toxic
  • Adaptable to many shapes

  • Light weight

  • Adaptable to many shapes

  • Can be used in floors, walls and ceilings

  • A vast range of organic finishes

How is Hempcrete applied?

Mechanical spray application

Mechanical spray application was developed in Europe by experienced Hempcrete engineers from France, England, Wales, Belgium and the Netherlands.

Like conventional casting in situation, a timber frame is constructed as Hempcrete is non-structural and the timber structure is made to the relative local building codes and standards.

The window and door penetrations are formed using plywood or similar.

The walls are lined with Jude Hessian as a temporary support of the hempcrete as it is installed. Typically, two thirds of the wall is bulk filled, the hessian is removed, and the installation continues on the opposing side.

Two machines distribute the lime and the hurd to a lance.

The lance is aimed to the target area and the two ingredients are propelled out at various rates to ensure a good mix ratio is achieved in accordance with the manufacturer’s recommendations.

The method increases the speed of the installation. It also requires less formwork, that eventually results in landfill making the impact to the environment less.

Casting in Situation

Casting of the hempcrete is the primary installation method for applying Hempcrete as walls.

A timber frame is constructed as Hempcrete is non-structural and is made to the relative local building codes and standards.

A sheet of form ply (or similar) is applied as a temporary shutter, while the mixture is made in a mixer it is transported via buckets, poured into the formwork and gently tamped down to bind.

Working upward in approximately 60cm lifts until the wall is completed requires a skilled trade such as a carpenter to facilitate the formwork carpentry.

The mixing and placement of the Hempcrete mixture is an activity that can be done by people of all ages and skill sets, typically under the supervision of a trained Hempcrete installer.

The cast insitu method is used deliberately by experienced professionals where the desire is to achieve an exposed or “feature” wall within the inside surface of the project.

By adding various oxides in each batch, layer or as desired it is possible to create artistic finishes that are captivating to the eye.

Are there warranties or guarantees with Hempcrete?

OzHemp Tradical® Hempcretes are a combination of the highest quality hemp hurd and formulated lime.

Tradical is a French company therefore the product is currently imported into Australia. This recipe is the only certified method in Australia, which allows the homeowner to acquire adequate home insurance and warranty of the product is held for 5 years by the manufacturer. It is recommended the product is installed by a certified installer and the render is applied by a competent trade person.

What finishes are used on hempcrete?

Hempcrete must always be rendered on the external surface of a building as it is not resistant to the weather elements.

The formulated limes used vary and there are many recipes to consider.

Tradical® Lime renders are certified to be used in Australia, with a certificate of conformity supporting the use of the products on residential and commercial projects.

The lime render used externally contains a water repelling agent, which makes the render less able to absorb water and moisture. Mixed with locally resourced sand and water, the render is applied in 3 coats to achieve an overall 25mm thickness.

Fibreglass reinforcing mesh is applied to the base coat which assists in the reduction of surface cracking.

The final product typically varies with the type of sand used. Factors may include:

  • The location of the quarry

  • The sand type i.e. Plasterer’s sand or brickie’s sand

  • The total amount of “fines” in the sand

  • The tone and visible colour of the sand

Adding natural oxides to the render can add colour and variety while maintaining the water repelling properties of the external render.

Primary colours are used in various ratios to create the colour of taste and can be an architectural component to the building.

The internal face of the Hempcrete wall is also rendered with the formulated lime, though this lime is not required to have the water repelling properties. It is encouraged to use the external grade lime in the wet areas for piece of mind.

The lime and sand mix used internally is mixed and applied in the same manner for the external surfaces.

Oxides may also be used to achieve the colour of choice.

Quite often, a gypsum or clay based plaster is applied at +/- 5mm thick.

This finish creates a “venetian” type plastered finish that is able to be left in a burnished state..

There are many varieties of products that may be used, though it is encouraged that the permeability of the product is maintained to not supress the properties of the Hempcrete’s breathability.

The use of lime based and permeable paints can also be used.

These paints are encouraged to not supress the properties of the Hempcrete wall.

Often, the paint is applied to a gypsum based plaster that has been applied to the lime render.

The paint may also be applied directly to the sand finish render.

It is not recommended that the paint is applied directly to the Hempcrete wall.

There is much to explore and experience when it comes to finishing the Hempcrete, it is important to consider your needs for durability, aesthetics and overall architectural appearance of the project.

How much does it cost to install Hempcrete?

The current estimated cost for Hempcrete material is based on market price plus the cost of freight from Europe to the local port, then transport to the designated location. The cost of the project will be dependent on the desired wall thickness, the height of the walls, site logistics and the method of application. The lime render should also be factored in while calculating the overall cost of the build.

The most challenging component of cost estimating comes to the application of the product. Where conventional cast in situ method is required, the labour cost is increased due the various tasks that must be undertaken including formwork, mixing, moving, placing and tamping.

Currently, the most cost effective method of application is mechanical projection. This requires less labour and can be applied about five times faster than the conventional cast in situ method. The mechanical projection method also uses one quarter of the formwork, in turn reducing the set-up costs for the project.

In Australia, many homeowners turn to doing workshops or encourage the public to experience Hempcrete installation by donating their time. This is a great way of establishing a community-based program, meeting new people and learning a new skill. It is recommended the workshops are supervised by an experienced Hempcrete installer to ensure the product is installed in conjunction with the Tradical OzHemp installation guide.

Mechanical projection is approximately 3 times faster than conventional Hand placement” Cameron Richardson

Is Hempcrete Safe?

Hempcrete is perfectly safe as a building material for people and pets.

There are no Volatile organic compounds (VOC’s)

No chemicals are added and does not release off gasses or toxic fumes

It is hypo allergenic, therefore does not trigger any allergies or respiratory illnesses

Does not ignite and is non-combustible in the presence of fire