by Alex Sparrow and Jennifer Martin

As natural builders, a large part of our approach to construction is to design and construct buildings with as low a carbon footprint as possible. In order to be successful at this, it’s essential to keep our material sourcing local, and avoid the big carbon hitters – concrete, plastics, foam insulations, imported sheet goods, chemical paints, etc., even though these items are ubiquitous in the building trades. Staying away from these materials is no small feat in the modern construction industry, and we’re thrilled to be a part of a burgeoning US Hemp Building industry that aims to combat the need for these materials in our assemblies.

While the industry has been steadily growing in Europe over the last 30-40 years, recent changes in the US legislature mean that hemp building is only recently beginning to pick up pace here in the USA. Naturally, perhaps, alongside the early development of the emerging industry’s infrastructure, a conversation is underway about the preferred terminology to describe the star of the show; “hempcrete”, or “hemp-lime”; a material formed from the chopped stalk of the industrial hemp plant, wet-mixed with a mineral binder, this binder typically having lime (CaCO3) as its largest constituent.

At this pre-scale stage of our new industry, it could be argued that we have a unique opportunity to actively choose terminology to describe the materials we use. So in this article, we explore the nomenclature of the hemp building industry, and the possible impacts, both positive and negative, that decisions about terminology might have on our industry as we move forward.

Our own languageing journey

We should note, at this point, that the views expressed here are the product of a conversation between the two of us. Jennifer, as a natural builder – although a relatively new practitioner of hemp-building, brought certain pre-conceptions to the topic; some of which were reinforced, and some challenged, by Alex in his role as “old timer” from the European hemp-building industry.

We feel that exploring these ideas together has been valuable to us, and wanted to share our resulting thoughts with you here. We’d love to hear your views too!

Current terminology: love it, or hate it?

The terms Hempcrete and Hemp-lime are used interchangeably to describe the biocomposite insulation and walling material produced when chopped hemp hurd is mixed with a mineral binder. Various proprietary binder mixes exist; most of which are currently imported to the USA from Europe, to bridge the gap until USA produced binder mixes are formulated, tested and brought to market here.

The two terms are both straight translations from the French (France being where hempcrete was first formulated) and the terms Beton de chanvre (Hemp concrete), and Chanvre chaux or Chanvre et chaux (hemp-lime, or hemp and lime) are also used interchangeably there.

When the material was first used in England in the late 1990s, the term “hemp concrete”, was quickly contracted to the catchier, and possibly more marketable, Hempcrete.

While all in the industry understand the two terms to mean the same thing, it’s striking that many don’t really like the term hempcrete, preferring hemp-lime because it avoids the perceived connection to concrete; the ubiquitous structural construction material formulated from ordinary portland cement (oPC), sand and an aggregate – usually stone.

In fact, concrete as a noun has two definitions, it’s just that the construction material is the better known one among the public at large:

Concrete (noun):

1 : a mass formed by concretion or coalescence of separate particles of matter in one body

2: a hard strong building material made by mixing a cementing material (such as portland cement) and a mineral aggregate (such as sand and gravel) with sufficient water to cause the cement to set and bind the entire mass

Source: Marriam Webster

An aversion to the term hempcrete is Jennifer’s starting point. She is a natural builder, after all, and knows that concrete and cement production are very high embodied carbon materials, and are responsible for a significant amount of the world’s carbon emissions, partly because of their raw materials and energy intensive production methods, and partly because of the ubiquity of their use (cement is the second most used material in the world, after water).

Jennifer is also frustrated by explaining to people why hempcrete is different to concrete as the starting point for conversation (“no it isn’t load-bearing”, “no, you can’t use it below grade”, “yes it’s more expensive than concrete – but it does lots of things which concrete doesn’t do!”), all of which she feels could be avoided by the use of a different name.

Alex has a slightly different perspective on this; pointing out that the blogs and websites of American hemp advocates – which 5-10 years ago usually proclaimed that “hempcrete does EVERYTHING that concrete does but is 7 TIMES STRONGER!” – are now carrying more in-depth, accurate and better fact-checked copy. This is a sign that progress is being made in educating the hemp community about hempcrete’s properties – now for the construction industry and the rest of the population!

While Alex admits that hempcrete isn’t a perfect term for the material, it is the one that has (so far) caught the imagination of the general public in the English speaking world, and he feels that the value of this might just outweigh the “inconvenience” of the inevitable discussion about the differences and similarities with concrete.

After all – what better way to start a conversation about our favorite material’s exceptional properties than by referencing one of the most-used materials globally, and benefitting from an existing conceptual framework that is already understood by probably at least 7 billion people worldwide?

In fact, concrete is such a familiar material, term, concept, that hempcrete immediately means something to everybody. Try it out for yourself… “I work with hempcrete. Have you heard of it?” The response tends to be along the lines of “No… but I imagine it’s like concrete but made from hemp, is that right?” and then you’re off; filling in the details for them to flesh out their understanding of the similarities, the differences, and the huge benefits that hempcrete offers.

 

Semantic Analysis  –  Concrete vs. Hempcrete
Similarities Differences
both use formulated  lime Concrete Hempcrete
both are wet-mixed and formed, either as used on site, or in precast products
both are aggregate-binder composites stone or gravel and sand as aggregate hemp as aggregate
both are mass building materials load-bearing non-load-bearing (typically)
application above or below grade above grade only
insulation capacity sometimes insulating always insulating
thermal storage capacity high specific heat capacity (high thermal mass) moderate specific heat capacity (moderate thermal mass)
vapor permeability low vapor permeability high vapor permeability
net carbon emissions ~900 kg carbon emitted

per metric ton

~325 kg carbon stored (absorbed) per metric ton

 

Hemp-lime on the other hand, in the ears of someone who has never heard the term before, doesn’t automatically mean anything – neither to listeners in the construction industry, nor in the wider public, and that might be the single biggest argument against using it.

Of course, you can argue that wider use of hemp-lime might change this situation, but given that both terms have been used interchangeably over the last 20 plus years, we are left in no doubt about which name has been shown to have the most impact; both in marketing and awareness-raising among the general public.

However, leaving our personal responses and thoughts on marketing and public awareness aside, is there an argument for the accuracy or appropriateness of one term over the other? To put it bluntly, is one term better than the other when it comes to describing the material(s) that we use. As we will discover, that “(s)” might be the important factor to consider…

 

Lies, damn lies, and semantics: what exactly are we trying to name?

Most commercial hempcrete binders are, in essence, Formulated Hydraulic Limes (FL or FHL) – being made with a majority of hydrated air lime, plus some hydraulic lime and/or pozzolan and/or ordinary Portland cement (oPc) and/or other substances.

Other common ways of formulating a hempcrete binder with a lime-based mix include; (air)lime-pozzolan mixtures; Natural Hydraulic Limes (NHL), especially those from a class of very strong naturally occurring hydraulic limes called Natural Cements; and the addition of non-pozzolanic substances to air-lime to bond it together while it cures and dries out.

As most types of hempcrete can be used in different formulations for different elements of a building (floors, roof insulation, walls, trowelled mixes for solid wall insulation etc.), the resulting composite material regularly changes – in terms of its density, proportion of binder, and amount of water added – even when the same binder and hemp is used.

Builders in the USA looking for local solutions are largely sourcing dolomitic lime, which contains up to 50% magnesium. A metakaolin clay or other pozzolanic mineral is added and often makes up a high constituent proportion of the binder – some mixes include 40% by volume. Technically, the most appropriate term here is hemp-lime-magnesium-clay(or other pozzolan).

Typically the hemp+binder+water are the only things in the mix that makes up a finished hempcrete, however many other hemp insulation and walling materials have been created using, for example, hemp+lime+clay+water, or hemp+lime+sand+water, or hemp+clay+water. These mixes tend to produce a material which has less insulation but higher thermal mass, making them more suitable for hot climates. All of these materials would seem unlikely candidates for the name hemp-lime.

Likewise, it’s possible to switch out the hemp for another bioaggregate, often something which is easier-to-source in local waste streams. To name but a few; sunflower stalk, sugar cane, rice hulls and coconut fiber have all been used successfully – with lime, clay or a combination of the two as a binder.

Then there is hemp-lime (or should we call it lime-hemp?) plaster; where hemp hurd, fiber, or dust is added to a lime plaster to introduce desirable properties; insulation, tensile strength, or increased humidity buffering.

While lime-hemp plaster is very definitely a lime plaster with some hemp in it (as opposed to hempcrete/hemp-lime; a hemp matrix bound together with a lime binder), there are also other things which sit in between the two. For example, it’s possible to add sand to a hempcrete mix to make it workable enough that you can trowel it onto an existing masonry wall, as solid wall insulation.

Easier to apply in a thin coat than hempcrete (at least for those without access to spray machinery), such mixes are still much less dense than a lime-hemp plaster, and so offer better insulation. Do we even have a term for this mix? Trowelled hempcrete? Hemp-lime-sand insulation?

In the USA, plasters often have other materials added to aid in tensile strength and workability, e.g. small bits of straw, cattail fluff, cow manure, etc. and natural builders tend not to refer to these in the nomenclature, instead using the generic term lime or clay plaster. At the time of writing, insulating lime plasters are not commonly used in the USA, so terminology has not yet developed and arguably the type of insulating aggregate may not make it into the name of the plaster.

 

Terminology Conclusions

As can be seen, when we define clearly what we are referring to, the term hemp-lime seems somewhat inadequate, not really covering the complexity or the range of the different composite materials we are talking about.

Nor, if we really hold it to account, is hemp-lime a very accurate term. After all, exactly zero hempcrete binders are made from “just lime” – all of them involve adding something else to cause a hydraulic reaction or otherwise alter the properties of pure lime. This is essential to make lime capable of binding thousands of tiny particles of plant material into a solid mass whilst holding itself up, until the lime sets and the composite material dries. Even the strong (NHL) Natural Cement binders are derived from a naturally occurring limestone which is so contaminated with other minerals – giving it its cementitious properties – that it actually contains very little pure lime.

Hempcrete probably works better as an overall descriptor then, with its “full name” of hemp concrete, meaning “a mass formed by concretion or coalescence of separate particles of matter in one body, one of which is hemp.”

By referring to the finished composite, the binder material is left undescribed, and this suggests a hierarchical relationship between our two terms; hempcrete being a term that would encompass, for example, hemp-lime, hemp-clay, hemp-lime-clay and hemp-lime-magnesium-clay.

Of course, when the aggregate changes, so does that parent term, and sunflowercrete, sugarcrete, ricecrete or cococrete, would logically also cover a range of formulations using different binder materials.

Crucial Takeaway

In our conversations, once the bell had rung on the final round of hempcrete vs. hemp-lime, we found ourselves seeing the question of terminology as perhaps less important than, and a possible distraction from, the important tasks currently facing the US Hemp Building Industry. We need to grow public awareness,  ensure market adoption, and develop the industry in order to change the world.

Perhaps it’s time the industry as a whole worried less about terminology and focussed our collective energy on the tasks in hand bring about market adoption throughout the industry?

 

Where do we go from here?

1.      Grow public awareness with clear communication

Embracing the term hempcrete requires a thoughtful framing of this biocomposite as distinct from its ubiquitous concrete counterpart. Hempcrete, as a novel material, is not widely understood in the general population, and all of us on the front lines wind up repeating the same few basic corrections over and over. It’s therefore imperative for those of us inside the industry to communicate intelligently about these materials and frame the discussion such that professionals and lay people alike walk away with a robust understanding of what hempcrete is, and is not.

  • Frame conversations about hempcrete as an insulation-thermal mass biocomposite mix that forms a mass.
  • Talk about the definition of concrete as a mixing of multiple materials into a single body so that the term hempcrete makes sense as a viable name for this biocomposite.
  • Connect the dots of concrete and hempcrete as both lime-based formulations with common properties of flexibility of form, mold and pest resistance, and fireproof nature.
  • Talk about hemp hurd as a strong, carbon-storing material used throughout history and capable of globally local production.
  • Explain that hemp absorbs so much atmospheric CO2, that hempcrete is still a significant net carbon-storing material.
  • Dicsuss the health and well-being advantages which the vapor permeable nature of hempcrete brings to building occupants.

2.      Ensure market adoption through education and specificity

The US Hemp Building Association has a responsibility to guide public perception, manufacture and use of hempcrete. As an organization, we should lean on the collective wisdom gained from businesses, researchers, and enthusiasts around the world to better understand, engage further research into, inform our membership and educate the public about, the finer points of the biocomposite.

We also need to learn how to utilize local materials effectively and develop an accurate terminology alongside this. US limes have different properties than those available on the European continent, and the US possesses other agricultural products and waste streams that are begging to be put to use as aggregates. We need to:

  • Define the properties needed in binders and aggregates to create viable biocomposite construction materials, with the appropriate technical performance.
  • Keep our terminology open enough to allow the use of a range of different binders and aggregates in response to regional availability.

This clarity supports not only rapid awareness-raising among the building trade and the general public, but also the clear definition of what properties hempcrete and other biocomposite materials should have.

A clear and accurate description of these properties will enable the ASTM to publish a general hempcrete specification, and this in turn can be used to ensure that all new hempcrete materials launching in the marketplace will meet defined minimum standards for technical performance and durability.

3.      Develop the hemp building industry

Although beyond the scope of this article, there is a tremendous amount of other work to be done to create a hemp building industry. Everything, from code inclusion to supply chain development, seeking approval from financing institutions, research and development, to professional standards and construction best practices must be either created or refined for the US. Though it can seem daunting, the US Hemp Building Association is committed to leading the work in each of these areas and needs your help.

To be successful as a burgeoning industry, we need a common language, a deep understanding of hempcrete, and a framework for appropriate discussion of these stellar biocomposites. This takes time, effort, and the cooperation of all to ensure that our knowledge base is up to date and robust.

4.      Transform the built environment and change the world

It’s not everyday that a building system or technology comes along that has the power to change the climate trajectory.

Hempcrete, as a carbon-storing biocomposite, provides a clear and positive trajectory for addressing the most vital human need of shelter at scale without polluting the planet in the process. The positive implications of growing hemp for the health of our soil reinforces a symbiotic relationship between land and the shelter we need, and the abundance of lime and clay throughout the world provides an opportunity to use local mineral deposits wherever you are.

This integrated perspective is a radical shift from business-as-usual, and paves the way for a transformation in how we build. By acting responsibly with the natural resources in and around our communities, hempcrete offers a way to regenerate damaged systems and revitalize the communities we live in.

Just imagine – biking past hemp fields that are literally growing the building materials we use. Think about the transformative power of utilizing local mineral resources responsibly – engaging stewards who understand the limits of their use, who work to keep our communities vibrant and our air and water clean.

Hempcrete has the potential to define new ways of doing things better.

Authors parting thoughts

We believe that awareness raising and the dissemination of knowledge is the critical first step; educating ourselves, the wider construction industry, other related industries and the general public.

In order to do this, we need to be clear about our own understanding of the limits and properties of our materials, and adopt an equally clear nomenclature to reflect what we know about their differences and similarities.

We are the ambassadors for a new way of building. Together we can empower those constructing the built environment to make sane and responsible choices.

Though it may seem daunting, we are all pulling together to manifest a resilient industry that invites diversity, innovation, and collaboration. After all, many hands make light work. Add your voice to the conversation by joining the USHBA network today.

 

About the Authors

Alex Sparrow

Alex Sparrow, Founder and MD at UK Hempcrete, is recognized globally as one of the leading experts

in the use of hempcrete and other bio-materials in construction. He co-authored The Hempcrete

Book (2014), widely acknowledged as the definitive guide to this remarkable building material.

Alex sits on the board of the Alliance for Sustainable Building Products in the UK, and speaks

internationally on hempcrete, as well as providing training and consultancy services with a global

reach, to assist others in the use of hempcrete and bio-based construction materials.

UK Hempcrete Ltd.

UK Hempcrete is a company providing specialist contractor services in construction, known for its innovation in zero-carbon buildings, and the construction of the structural and thermal envelope from renewable and/or recycled materials. UK Hempcrete provides specialist hempcrete, limecrete, timber framing, natural insulation & lime plastering services to domestic and commercial clients.

www.ukhempcrete.com

 

Jennifer Martin, MA CSL, CPHC, PMP

Jennifer Martin, Catalyst at HempStone works collaboratively with industry leaders, disruptors, and pioneers to create radically responsible architecture based on building performance and climate responsibility. A natural builder by trade, Jennifer led a design/build construction firm at Dancing Rabbit Ecovillage, a sustainable and cooperative-living community in Missouri. Jennifer’s unyielding enthusiasm for sustainable architecture coupled with her zest to collaborate in order to push the envelope of what is possible makes her a catalyst.

HempStone, LLC

HempStone is committed to helping build carbon-beneficial infrastructure. Based in New England, we provide consultation, construction, supply, and training services for hempcrete and other natural building systems. HempStone conducts research and testing of local materials and partners with farmers, processors, and manufacturers to help bring carbon-storing solutions to market. HempStone is proud to serve as a critical connector, operating collaboratively throughout our growing network to drastically reduce the carbon emissions of buildings.

www.hempstone.net

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