Towards a Sustainable Tomorrow
TRADICAL® HEMPCRETE
FREQUENTLY ASKED QUESTIONS
Tradical® Hempcrete is a relatively new building material in Australia, so no question is considered a silly question. No matter how much information you put out there, some questions will always remain.
We hope you find our list of Frequently Asked Questions helpful. If you have a question that has not been answered, please contact us.
FAQ – Tradical® Hempcrete Material
Tradical® Hempcrete is a mixture of lime, hemp hurd and water that will petrify into a bio-composite substitute. Watch the video below for further details.
Tradical® Hempcrete is normally installed together with a timber or steel frame, with the vertical load of the roof and upper floors transferred through the frame. Tradical® Hempcrete can be used to provide racking strength to the frame if required. However, Tradical® Hempcrete by itself is a non-structural and lightweight material, so it is not suitable to use for load-bearing walls.
We recommend 250-300mm for most domestic applications.
Yes, there are various application for Tradical® Hempcrete!
- Insulating walls
- Insulating ceilings/roofs
- Insulating floors/screeds
- Hygrothermal coatings
- Renders
Tradical® Hempcrete can be used for providing roof insulation as this ultra-low density and lightweight material is ideal for saving energy and contributing to a high level of thermal comfort.
Tradical® Hempcrete combines a low density (as low as 220 kg/m3) with excellent insulating properties, an exceptional elasticity (due to the composite effect of the hemp hurd and the lime matrix) and vapour permeability.
For these reasons due to the simplicity of its installation methods, Tradical® Hempcrete is a very practical solution for roof insulation in both new builds and renovation applications.
Yes, Tradical® Hempcrete can be used for bathroom walls and finished with lime or clay plasters to allow it to breathe and regulate moisture. In Europe, lime materials have been used for ages in bathrooms without the need for extraction fans. Please refer to our installation manual for options on bathroom walls.
Tradical® Hempcrete walls are normally finished with a lime render or covered with a rain-screen cladding (masonry or timber) of some sort to protect them from the weather.
Building Research Establishment (BRE) Scotland have conducted water penetration determination tests on walls constructed from a mixture of hemp and lime mortar. On completion of the 96-hour water spray test, there was no evidence of water penetration through the complete thickness of any of the four test walls. The results provided indicate that the render coating remains well adhered and crack free, it is unlikely that rain penetration will transverse the complete thickness (200mm) of the hemp/lime mortar wall.
Tradical® Hempcrete is certified – BAL FZ (Achieved in compliance with FRL) making it suitable for use in all bushfire prone areas (Low to Flame Zone) and has achieved a Fire-resistance of building elements – FRL73/73/73.
Yes! The word breathability is often used to describe Tradical® Hempcrete buildings. There are various ways in which materials deal with moisture such as water vapour permeability, capillarity and hygroscopicity. Tradical® Hempcrete performs well in all these areas to provide a healthy internal environment.
Tradical® Hempcrete walls are normally finished with a lime render or covered with a rain-screen cladding (masonry or timber) of some sort to protect them from the weather. The usual finish applied for external walls is a two-coat Tradical® PF80 lime render, which has water repellent properties.
Building Research Establishment (BRE) Scotland have conducted water penetration determination tests on walls constructed from a mixture of hemp and lime mortar. On completion of the 96-hour water spray test, there was no evidence of water penetration through the complete thickness of any of the four test walls. The results provided indicate that the render coating remains well adhered and crack free, it is unlikely that rain penetration will transverse the complete thickness (200mm) of the hemp/lime mortar wall.
Yes! Tradical® Hempcrete is protected against rodent, termite and insect infestations thanks to our Tradical® lime binders.
Yes! In addition to the breathability and water absorption properties of Tradical® Hempcrete, the natural lime binder in Tradical® Hempcrete acts as a repellent to dampness and mould.
To calculate the R value, divide the thickness of the wall (in meters) by the thermal conductivity (W/m.K). The thermal conductivity of hemp is approximately 0.076.
So, a 300mm thick wall is approximately R4.0.
Tradical® Hempcrete is used to build monolithic walls as it is extremely air-tight and air leakage through the walls is negligible. The actual figure is approx. 0.75 g/m2/mmHg. Typical air leakage is 1.0 – 3.0 Air Changes/hour at 50 Pascals.
Spray applied Tradical® Hempcrete locks up around 110kg of CO2 per cubic metre. Shuttered and cast-in-situ Tradical® Hempcrete locks up around 110kg to 165kg of CO2 per cubic metre, depending on the level of compaction during construction.
Tradical® Hempcrete does not exhibit the compressive strength associated with concrete as it is not a dense material, and it is not a load-bearing structure like concrete is.
However, Tradical® Hempcrete is very lightweight, up to eight times lighter than concrete, and lacks the brittleness of concrete, eliminating the need for expansion joints. Concrete weighs 2400kg per cubic meter whereas Tradical® Hempcrete weighs 280kg per cubic meter.
Tradical® Hempcrete also has obvious advantages over concrete as it is also a carbon sink, a strong insulator, non-toxic, fire-resistant, pest-resistant, mould-resistant and an efficient moisture regulator with breathable walls.
The cost to build with Tradical® Hempcrete depends on the scale and design of the build and the method of installation. Tradical® Hempcrete that is spray-applied is more cost efficient than cast-in-situ and is comparable with conventional construction costs.
Contact us today with your required specifications for a free quote!
Tradical® Hempcrete materials can be purchased directly from OzHemp, the exclusive authorized distributor for Tradical® products in Australia and New Zealand.
Tradical® Hempcrete materials can also be purchased from authorised resellers.
OzHemp is currently the only supplier of BCA (Building Codes of Australia) certified hempcrete products and installation methods in Australia and New Zealand, according to The Australian Building Codes Board (ABCB).
Contact us today for all enquiries or a free quote!
For technical details and sources, visit BCB Tradical.
FAQ – Tradical® Hempcrete Construction
Tradical® Hempcrete is usually mixed in a large pan mixer for quick and optimal mixing. It can be done in a conventional drum cement mixer, in which you can mix 100 litres of hemp with the required ratios of lime binder and water. Add the water first followed by the binder, mix for 2 minutes, then add hemp and mix for another 1-2 minutes until all the hurd (shiv) is covered with the lime binder. The hemp hurd, binder and water should be mixed for the minimum time possible, to ensure a consistent mixture of the binder is evenly distributed and coats all the hemp hurd. Mixing for longer than necessary (especially in a drum mixer) will cause the mix to start “balling”, where small balls of binder start forming in the mixture.
The main consideration with steel is the risk of corrosion, owing to the alkaline nature of the lime binder in Tradical® Hempcrete. Wet lime attacks the zinc on galvanized pieces which creates possibility for future corrosion. All galvanized parts that come into contact with wet hempcrete must be painted. Once fully cured, this is no longer an issue as cured hempcrete tolerates galvanizing just fine.
Any metal fixings within a Tradical® Hempcrete wall that are exposed to the material – however, minimally – such as screws, joist hangers or straps, should be of stainless steel or galvanised steel that can be pre-painted with an anti-corrosion coating and painted again once installed, in case the process of fixing has removed some paint, to protect it from corrosion. Therefore, these metal fixings should only be used as a last resort.
No, the timber frame encased in Tradical® Hempcrete will not rot. This is due to the transition in humidity inside the Tradical® Hempcrete structure. Tradical® Hempcrete walls and timber are both hygroscopic, meaning it’s able to absorb or adsorb moisture/water from its surroundings. The vapour-permeability and hygroscopic nature of Tradical® Hempcrete means that the timber framing is preserved whether it is treated or untreated.
A wall cavity will not be required as Tradical® Hempcrete walls provide insulation and is used as a monolithic (solid) walling material.
Sand changes the density of the wall structure, resulting in a denser/heavier wall, thereby compromising its performance characteristics, reduction of thermal rating, breathability and restricted movements. The presence of cement and sand will prevent hempcrete from “breathing”. Hempcrete walls need to “breathe” to ensure there is interaction with both the internal and external environments. This allows for the hempcrete to absorb/desorb water vapour (humidity), as well as the ability to buffer temperature fluctuations.
The only reason sand would be used is when the lime binder is an inferior product. We do not recommend the use of sand due to the loss of insulation value, the loss of breathability and the increase in weight, which will also result in additional costs to strengthen the footings. Overlooking the latter will result in buildings suffering from cracks years later.
All finishes for a Tradical® Hempcrete wall must be vapour permeable to ensure the continued health and breathability of the wall. The usual finish applied for external walls is a two-coat Tradical® PF80 lime render, which has water repellent properties. Tradical® Batir lime render or clay plasters can be used internally. All paints must be vapour permeable, often used are lime or clay paints and limewash. Other finishes include timber or tile cladding with a vented air gap or stone or brick cladding with lime mortars.
Depending on the environmental conditions, Tradical® Hempcrete typically will dry out in 4- 6 weeks, allowing for plastering when the moisture content is around 15%. Plastering too early can cause cosmetic staining of the plaster due to tannin stains. Plastering also covers up the surface of the wall, reducing the surface area for evaporation and slowing the drying time of the wall. This means the Tradical® Hempcrete wall will take longer to reach its optimum thermal performance, so it’s important not to apply wet finishes too early.
All finishes for a Tradical® Hempcrete wall must be vapour permeable to ensure the continued health and breathability of the wall. Choose only lime, clay or mineral based paints. Limewash is often used for a Tradical® Hempcrete wall.
Generally, the cast-in-situ method is used for smaller projects that are less than 50-70m3, or where labour is provided by self-builders or volunteers.
The mechanical spraying of Tradical® Hempcrete becomes more economical for larger projects that are more than 70m3. The mechanical spray-application of Tradical® Hempcrete is a very quick and efficient method of hempcrete construction that allows excellent consolidation and consistency of the product. The spray application is the perfect solution to enhance the performance of Tradical® Hempcrete for its properties in a more convenient, faster and affordable method.
As an indication, for an average job with the casting in situ method, there would be an approximate cost saving of 14% using the spray application method.
Contact us today to discuss installation methods for your project!
Yes, providing the temperature is not below 5°C and the material is protected from frost and heavy rain, Tradical® Hempcrete can be installed in the winter.
Yes! Tradical® Hempcrete can be used in renovations to form infill panels for historic timber framed buildings.
For examples of such renovation works, visit www.bcb-tradical.com/en/our-achievements/.
Tradical® Hempcrete is non-load bearing, so the height limitation is only on the structural frame and in the engineering work.
There is no real limit other than practical arrangements on the site.
OzHemp is committed to providing the highest quality products and greatest accessibility to training and support to the builders and tradespeople within Australia. A team of competent Tradical® Hempcrete certified installers are available Australia-wide to assist you in getting your hempcrete project to fruition.
We also have access to numerous Building Surveyors, Architects and Builders to assist you with your planning, design and council submission.
Contact us for a list of trained and certified Tradical® Hempcrete contractors/installers for your project!
FAQ – Tradical® Hempcrete Maintenance
The use of plant-based materials mixed with mineral binders such as lime or clay go back thousands of years. Due to its high pH levels, good capillarity and vapour permeability, we know that the effects of the lime binder create a perfect environment in which to preserve the hemp hurd. Consequently, we are confident in anticipating that Tradical® Hempcrete buildings have a lifespan measured in centuries.
Tradical® Hempcrete carries a manufacturer’s warranty covering the replacement of any defective material. A trained, certified and approved Tradical® Hempcrete contractor or sub-contractor installing Tradical® Hempcrete would warrant the work, subject to the conditions of each contract.
Tradical® Hempcrete® is approved by the NHBC or the Zurich insurance schemes and complies with their low and zero-carbon housing technical standards.
The 3 insurability commitments made by Tradical® are:
Commitment to correct performance
BCB guarantees the compatibility between the recommended products and is committed to correctly performing blends on condition that they are used in compliance with the application instruction sheets, each corresponding to a specific use.
Performance ratings of recommended blends
BCB has had the tests required by the French Professional Rules carried out in accordance with the corresponding procedures and confirms the compatibility of the results with the expected threshold values (documents available on request).
Mastering application
Tradical® Hempcrete must be only to be installed by a suitably qualified tradesperson. OzHemp and BCB have been offering professionals a specific training programme to learn how to prepare Tradical® Hempcrete, as well as how to apply them within the fields covered by the regulation.
Dwellings built with OzHemp Tradical® Hempcrete are insurable in Australia and New Zealand.
The BCA certification of OzHemp Tradical® Hempcrete gives great confidence to councils, governing bodies and insurance firms to ensure that there is no compromise on insurability and building approval.
Tradical® Hempcrete is approved by Zurich Insurance and complies with their low and zero carbon housing technical standards.
Please contact us if you are having any issues with specific insurance brokers or insurance companies.