What’s binding it together?
You guessed it, a binder!
So what’s in the binder? And how does it stick everything together so well?
The binder consists of either hydrated lime or hydraulic lime. Or what is often referred to as Roman Cement.
Let’s dig a little deeper….
This article was contributed by Will Brain of Respirabuilt. Edited by Jeremy Thomas
Hydrated Lime
Hydrated lime is made by kiln-firing pure limestone. The firing process removes the carbon molecules from the calcium and converts it into a fine dry powder.
When the time comes to use that powder as a binder or mortar, you introduce carbon dioxide or air, essentially converting the lime back into limestone as it absorbs surrounding CO2. This is what is being referenced if you ever heard some talk about the carbon cycle, carbon and calcium are desperate to get back together. In fact that’s why the lime starts to set as soon as you open the bag!
Hydraulic Lime
Hydraulic lime, just like hydrated lime, is also kiln-fired using the same process. But hydraulic lime has added or existing impurities known as pozzolans.
So why add impurities and why give it such an exotic name?
Pozzolans can be a range of different things such as volcanic ash, brick dust, cement, crushed shells or in the case of our Hempcrete blocks; a probiotic fluid…more on that later…
Pozzolans. Great name. Great story…
History tells us that 2500 years ago the Romans quarried up volcanic ash to add into their lime mixes from a place known as Pozzuoli. The work was done under the watchful gaze of the active volcano Vesuvius near Naples in the Campania region of Italy.
So why did the Romans mix volcanic ash into their mortars?
What the Romans had discovered was that with this addition, their mortars would set stronger and faster and even set underwater! The addition of pozzolans causes lime to achieve a chemical set. In this process the lime returns to limestone in the presence of CO2 and water. This set is quicker and stronger.
Setting can also occur deeper in hempcrete walls where there isn’t an abundance of CO2 for hydrated lime to set within a convenient time frame.
Hurd is sticky stuff
One tremendously interesting fact is that hemp hurd has a high silica content. And silica just so happens to also be a pozzolan. So the actual hemp itself serves not only as an insulative aggregate, but to increase the strength and set speed of the lime.
At RespiraBuilt, we use a probiotic fluid in combination with lime to create our prefabricated hempcrete blocks. This fluid contains an abundance of carbon dioxide. This additive of course speeds up the lime carbonation process without the addition of cements unlike other hempcrete systems.
There are many benefits of using lime blends instead of modern portland cement. Lime based binders have far more plasticity and vapour permeability than modern cements which allows moisture to pass through structures without causing the destructive ponding processes we can see in modern construction. Following that concept water can create valleys, or holes, which destroy concrete. This will eventually erode even structures like the pyramids. So we should do anything we can to avoid water sitting, pooling or generally hanging around as it will eventually destroy homes and other structures.
Consider the Colosseum or the Pantheon, structures that stand the test of time. Structures which don’t compete with moisture, but let it simply pass through. This helps us understand the benefits of traditional mortars and binders. It is also one of the many reasons that natural builders are so passionate about their methods. They’re often preindustrial, tremendously reliable, have a fraction of the carbon footprint, and stand long through the ages.
Thanks for taking the time to read this case study developed by Will Brain of RespiraBuilt and edited by Jeremy Thomas of Environmentarian for the Hemp Building Directory of Australia. We spend a great deal of time researching, experimenting and writing about Hempcrete.
This is because we all want to help as many people as possible to insulate their homes with a natural Australian grown, carbon sequestering building material that has a wide range of benefits. From the farmers who grow it, along the production line to the installers who are part of the building process, to the users of the structures who have fire proof, bug proof, insulated homes and structures saving them money over the long lifespan of their buildings. And all the way up to all humans on planet earth so we can sequester more carbon and use less fossil fuels and use hemp building as a tool in the fight against climate change.
This article was contributed by Will Brain of Respirabuilt.
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