César Cardoso: “Building with hemp is a true green alternative”

Stimulating innovation in modern architecture, using natural or recycled materials, with low environmental impact, is one of the priorities of Natura Matéria, a spin off of the University of Minho, founded in 2021 by Civil Engineer César Cardoso.. We spoke with César to understand the extent to which hemp can be integrated into these new, more efficient and sustainable ways of building.

Civil Engineer with a Master's Degree in Management, Technology and Construction Physics from the University of Minho, César worked for several years as a guest assistant on the Master's Degree in Sustainable Construction and Rehabilitation, later collaborating with the architecture firm SKREI. Seeking to create and support the development of new materials and sustainable construction techniques for companies in the construction sector. Natura Matéria provides consultancy services and sells products for construction that respect the new market demands in terms of sustainability, based on the concept of circular economy and healthy housing.

When and why did you start working with hemp?
In 2006, when my partner Rute Eires finished her master's thesis on “Unconventional Materials for Sustainable Construction Using Hemp, Paper Pulp and Cork” at the University of Minho. Later, in 2009, we produced some prototypes of lightened adobe with hemp shavings, which we presented at a conference and fair in Serpa, but it was in 2017, as a collaborator in the architecture company – SKREI, as responsible for the development and production of hemp blocks , which developed blocks for the first national construction of non-structural masonry incorporating hemp shavings. In 2020, this first building in hemp concrete masonry was completed, at Rua do Paraíso 331, in Porto, and later a temporary construction was carried out with an identical block, but with charcoal, which was visible until the end of February 2021. XNUMX at the Centro Internacional das Artes, in Guimarães. 

César was responsible for the reconstruction of a watermill in stone, wood and hemp concrete, in Guimarães. Photo: Natura Materia

What work and/or research have you been doing with hemp?
In the area of ​​hemp, I am providing consultancy to national companies for the application of hemp concrete in different prefabrication formats, blocks, structural and self-supporting panels. I am working on the reconstruction of a water mill in Guimarães, in wood and hemp concrete. After a series of initial characterization tests, a mixture with the incorporation of fibrous industrial waste and hydrated lime, without hydraulic binders, was selected. In the field of research and development, in 2021 I founded Natura Matéria, a spinoff from the University of Minho. The priority is to stimulate a culture of innovation in modern architecture, in terms of projects and works, using natural or recycled materials, with low environmental impact. It is also intended to be a link between Research and Development (R&D) in Universities, Industries and designers, to create and support the development of new materials and constructive techniques with low impact on the environment.

In terms of construction, what are the main advantages of this material?
Its insulating and acoustic properties allow it to be applied as an insulating material on walls, roofs and floors. In environmental terms, hemp chips or shavings together with lime allow a negative CO balance2, allowing to build with “Zero Carbon”. In addition to the environmental advantage and multiple applications of hemp concrete, it has a high vapor permeability (hygroscopic), passive self-regulation of temperature and humidity, and can be used with an integrated structure of wood, steel or reinforced concrete. It also has low density, fire resistance, comfort and dampening of interior and exterior noise. For the durability of constructions, this product requires knowledge of raw materials and their properties, sensitivity to water, curing times, etc. 

What is the estimated cost of building a ± 50 m2 house out of hemp?
The cost for construction can be 5 to 10% above the value for a traditional construction or even less. This cost savings can be achieved with the participation of a qualified professional, to guide both the design phase and the construction phase.   

In comparative terms, does building in hemp pay off compared to traditional houses? Because?
Building in hemp is a true green alternative. Compared to conventional construction, for applications on exterior walls, the constructive solution based on hemp does not require the application of thermal insulation and, therefore, bonding mortars, reinforcing mesh, fixing accessories, finishing mortars in part formulated with the addition of cement, etc. In addition, in dry areas of a house, such as bedrooms and living rooms, for aesthetic reasons, hemp concrete can be exposed, eliminating the extra cost of mortar and painting. The level of thermal and acoustic comfort is higher, which will represent a reduction in energy costs in the long term. 

Is it already possible to build with hemp in Portugal? How do you get the hemp?
Yes, it is possible and there are already some constructions. At present, and for large quantities, hemp shavings and the raw material for hemp concrete still have to be imported.

What are the main challenges of this sector in the current situation?
Massification of industrial hemp cultivation in Portugal, with processing of hemp grown in Portugal to obtain quality chips and fibers that can be used in construction and at a competitive price. 

What recommendations would you give to our government, taking into account the sustainability challenges that exist today?
Ensure and encourage as a measure, not only of environmental sustainability, but also economic and social, that more small producers grow and process hemp, so that it can later be used in construction.
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This report was originally published on issue #4 da Cannadouro Magazine