t’hempted by concrete
At the Form/Designcenter in Malmö, an exhibition about a sustainable house project in the countryside in Halland was on display in the summer of 2023. It is a poetic and nice little exhibition, well worth a visit. The construction is relatively innovative and has received research grants because of this. The main reason is that it is built from the material Hampakalk, which has come relatively recently to Sweden. The material appears fantastic. It consists largely of hemp fibre and limestone, is rot-resistant and non-combustible, carbon dioxide neutral, contributes to a pleasant indoor climate, and can be shaped and adapted to the users will.
However, there are two important questions, that make a lot of difference, not being answered here. First of all, what is the reason for this material not being the most used in the construction industry today? And secondly, how sustainable is this material compared to other sustainable building techniques?
To answer the first question, we can look at a very similar product that has been manufactured for decades, what is colloquially called Träullit (after the manufacturer of the same name). Träullit has almost exactly the same properties as Hampakalk, the difference is that it uses wood wool instead of hemp. Although hemp grows faster than spruce, which is used for wood wool, it is also grown on land that arguably should instead be used for food production. But why has not Träullit made any significant success as a construction material over the years? There is of course a good reason, and that is the poor load-bearing capacity. You have to build a wood or steel construction that supports the material and takes the weight of the roof, even in small buildings. And if you have to do that, there is little to no reason why you shouldn't build an ordinary studded wall with less messy and simple off-the-shelf materials. Or just a lightweight concrete block wall if it is a homogenous wall you are looking for.
The second question is partly answered by translating Hampakalk into English. In English, it has the somewhat more correct and revealing name of Hempcrete. Namely, it is a variant of concrete (which is made of gravel, water and cement), where the gravel has been replaced by hemp. Something that all architects should know by now is that the manufacturing of cement generates huge amounts of carbon dioxide in itself, there is no way around it with today's technology. To make cement the limestone is heated to over 1000 degrees (almost always with fossil energy), and enormous amounts of carbon dioxide are released that had been bound in the limestone itself. For every kilogram of cement produced, 0.9 kilograms of carbon dioxide are released. Mixing hemp into the concrete to compensate for its emissions looks a lot like greenwashing, not much better than offsetting carbon dioxide by planting trees in a far away land. Naming it Hampakalk and never mentioning the word cement is exceedingly misleading.
Hemp is a fantastic material that has the potential to play an important role in the building industry´s transformation away from fossil fuels. Hemp fibre is a potent insulation material that makes buildings into proper carbon sinks combined with a wood structure. Hempcrete though, is probably a dead end, a fairly low-quality construction material that has overstated its role in the fight against climate change.
