What is hempcrete?The hempcrete building material is comprised of the woody core of the industrial hemp plant, also known as herd or shiv, water and lime-based binders.

What is hemp?Hemp or industrial hemp is the common name used for varieties of Cannabis sativa that contain almost 0.0% T.H.C. The hemp plant grows quickly and is one of the most versatile and highest yielding biomass plants known. Hemp can grow without pesticide or agrochemical inputs, and sequesters large amounts of carbon dioxide (CO2) during the growing cycle. One ton of harvested hemp absorbs 2 tons of CO2.One hectare (2.5 acres) of hemp is sufficient to build a standard house. It grows up to 4 meters high in 14 weeks. 60% of the plant can be used for building.

Why build with hempcrete?Good thermal qualitiesHempcrete buildings have excellent insulation properties up to R4.2 when built to a the recommended 250mm thickness. The solid infill (monolithic) construction of hempcrete buildings means that air leakage and draft is drastically reduced. Buildings stay warm in cold weather and cool in warm weather without a constant input of energy to be comfortable.Through good insulation, considerable amounts of money and energy can be saved.BreathabilityThe hempcrete structure allows transfer of moisture through the walls and avoids condensation build-up. This means that the humidity and air quality inside the building are controlled.

Good acoustic qualities

Hempcrete walls have great acoustic absorption. A wall with render will reflect sound and remaining sound traveling through the wall will be absorbed by the porous constitution of the hemp wood and the hempcrete itself.

Carbon sequestrationDuring the growing cycle hemp sequesters largeamounts of CO2.1m3 of hempcrete locks in 150kg of CO2 i.e. approximately 5.4tons of CO2 per house. Although the manufacture of the lime binder does release CO2 into the atmosphere, the result is that hempcrete removes more CO2 out of the atmosphere than itcontributes, making it a carbon-negative material. Hempcrete complies to the ISO standard 14040

Fire resistanceThe lime in the binder makes hempcrete fire resistant.Hempcrete is non-combustable and has a fire rating FLR of 60/60/60.Bush fire rating is established to be BAL FZ: Flame zone.

Pest, mould and mildew resistanceThe lime portion of the mix acts as a biocide so that hempcrete buildings are naturally pest, mould and mildew resistant. In addition, hempcrete buildings provide an optimum humidity range in which mould and fungi do not grow.

Free of ToxinsMany building products and their manufacturing processes use and release large amounts of polluting components. The mix of hemp wood and lime creates a long lasting, toxin-free building product that can offer zero carbon constructions

Properties:> low density> high thermal insulation> high sound insulation> high thermal inertia> vapour permeability, the construction “breathes”> high elasticity> fire and pest resistance.

Hemp hurds are mixed with a combination of lime products to produce a light weight, insulating, breathing material.

The mixture of lime to hurds varies with the type of construction application and prevailing climatic conditions.

ConstructionShuttered, cast and tampedIn this instance temporary shuttering is fixed to the timber frame with tubular spacers to form the finished size and shape of the walls. The Hemcrete is mixed in the required proportions together with the recommended amount of water.  Standard Wall Mix is 1 bale of hemp shiv to 1.5 bags of binder (HB) with approx 40 litres of water per bale of hemp.   This material is then tipped into the shuttering and lightly tamped into place. After 24 hours the shuttering can be removed.

Sprayapplied1water.  Standard Wall Mix is 1 bale of hemp shiv ( HF) to 1.5 bags of binder (HB), the water is added close to the nozzle of the spray system by the trained operative. This material is then sprayed against temporary or permanent, single sided shuttering and flattened to the required surface. After 24 hours any temporary shuttering can be removed. 

Drying

High humidity levels and low temperatures can inhibit drying of Hemcrete.

Careful planning and preparation is required to minimise drying times through provision of proper protection to drying Hemcrete from rain and frost.  It can be appropriate to use air movers, heaters and dehumidifiers to shorten drying times during wet weather, cold periods, winter conditions or when building in exposed locations. 

MaintenanceHemcrete needs to be protected from the weather to maximise it's durability. As such the maintenance of Hemcrete is really the maintenance of elements that protect it from the weather. All of the following is common sense and good practice.

Surface finishesHemcrete needs to be kept dry and covered with vapour permeable surface finishes. These finishes (render, plaster, brickwork, stonework, timber cladding etc.) should be kept in good condition and only painted with breathable paint finishes or similar products.  Any product that is impermeable or reduces permeability will affect the durability of Hemcrete.

How are Hempcrete walls formed?Hempcrete walls are currently cast in place. Because Hempcrete

contains little free water, it does not exert hydrostatic pressure on formwork so heavy timber or steel staunchions as required with concrete formwork are no longer required. Lightweight formwork such as recycled plastic formwork or 6mm plywood boxing are sufficient to hold Hempcrete in position. The formwork (depending on site conditions) can be stripped within 24 hours for use on the next section of work.