Hempcrete FAQ

What is hempcrete?

Hempcrete is a bio-composite building material made from the woody core of the hemp plant, known as hemp shiv, and a lime-based binder. It is a lightweight, insulating material used for walls, floors, and roofs, offering excellent thermal and acoustic performance. Hempcrete is known for its breathability, allowing water vapor to pass through, which helps to regulate humidity and prevent moisture build-up.

What are the advantages of using hempcrete?

Hempcrete offers several advantages, including:

• Sustainability: Hemp is a fast-growing, renewable resource that sequesters carbon dioxide during its growth cycle.

• Insulation: Hempcrete provides excellent thermal insulation, reducing energy consumption for heating and cooling.

• Breathability: Hempcrete’s porous nature allows water vapor to pass through, regulating humidity and preventing moisture problems.

• Acoustic performance: Hempcrete effectively absorbs sound, creating quiet and comfortable interior spaces.

• Fire resistance: Hempcrete has a high fire resistance rating.

• Pest resistance: The lime binder in hempcrete deters pests and insects.

What types of lime are used in hempcrete?

Different types of lime are used in hempcrete, each with varying properties:

• Air limes: These limes set slowly through carbonation in contact with air. They are highly breathable and commonly used in traditional and natural building.

• Hydraulic limes: These limes set more quickly through hydration with water. They offer greater strength and water resistance than air limes and are categorized as feebly, moderately, or eminently hydraulic based on their properties.

• Proprietary binders: Specifically formulated for hempcrete, these binders often combine air lime with a proportion of Portland cement to achieve the desired setting properties and strength.

How is hempcrete installed?

Hempcrete is typically installed using a process called casting:

1. Shuttering: Temporary or permanent shuttering is erected to create the desired wall shape.

2. Mixing: Hemp shiv is mixed with a binder in a forced-action pan mixer or a conventional concrete mixer.

3. Casting: The hempcrete mix is poured into the shuttering and evenly distributed.

4. Curing: The hempcrete is left to cure and dry, during which it hardens and gains strength.

What are the considerations for finishing a hempcrete wall?

Hempcrete walls require breathable finishes to maintain the material's vapor permeability. Some options include:

• Lime plaster: A traditional and natural finish that complements hempcrete’s breathability and offers a range of textures and colors.

• Clay plaster: A natural finish with excellent moisture-buffering qualities, typically used internally due to its susceptibility to weathering.

• Cladding: Timber, slate, tile, brick, or stone cladding can be used, ensuring a ventilated air gap is maintained between the cladding and the hempcrete wall.

How does hempcrete perform in terms of structural integrity?

While hempcrete offers good compressive strength, it is not suitable for load-bearing applications. A structural frame, typically made of timber, is required to support the loads of the building. Hempcrete acts as an infill within this frame, providing insulation and contributing to the overall structural stability.

What are the key factors to consider for a successful hempcrete building project?

• Design: Carefully plan the building design, taking into account the properties of hempcrete and the integration of structural elements.

• Materials: Source high-quality hemp shiv and a suitable binder from reputable suppliers.

• Construction: Ensure proper installation techniques, including accurate shuttering, thorough mixing, and consistent casting of the hempcrete.

• Finishing: Select breathable finishes compatible with hempcrete to maintain the wall’s vapor permeability.

• Expertise: Consult with experienced hempcrete builders or professionals for guidance and support throughout the project.

Hempcrete up close

Where can I find more information and resources on hempcrete?

• The Hempcrete Book by William Stanwix: A comprehensive guide to building with hempcrete, covering materials, techniques, and design considerations.

• UK & US Building Limes Forum: An organization promoting the use of lime in construction, offering resources and training on lime-based materials and techniques.

• Hemp Building Association: An industry association dedicated to advancing hemp building practices, providing information, and connecting professionals in the field.