Bacteria-Fungi Mortar: Construction with Reclaimed Materials and Microbial Composite

The construction industry is one of the world’s largest consumers of raw materials, heavily reliant on energy-intensive and extractive inputs. Bricks, a material prized for their durability, often outlive the buildings they support—yet are discarded or downcycled because the mortar binding them is too strong to remove cleanly.

A new study by researchers at Aarhus School of Architecture and Ghent University explores a promising solution: replacing conventional mortar with a fully regenerative, bio-based alternative made from mycelium and bacteria. The approach could unlock large-scale reuse of clay bricks, reduce material waste, and open up a new chapter in low-impact construction.

Wall fragment prototype after 5 weeks of growth. Here, the white mycelium-bacteria based mortar gaps seem brown due to a few fruiting bodies and the distribution of brown spores of those, especially visible in the lower first third from right to left. Image credits: Hyun-Kieffer & al.

Rethinking Mortar: Co-Cultivating Fungi and Bacteria

The researchers developed a novel microbial binder called a mycelium-bacteria-based composite (MBBC). It uses Ganoderma lucidum (a filamentous fungus) and Sporosarcina pasteurii (a biocementing bacterium) co-cultivated on beech wood sawdust. The bacteria trigger calcium carbonate precipitation, helping reinforce the mycelial network with mineral deposits.

While pure mycelium composites are already known for their low energy footprint and biodegradability, the inclusion of S. pasteurii boosts adhesion and mechanical stability. In this setup, the microbes not only bind bricks but help shape a living material that grows into the surface of the clay, forming a reversible joint.

Three Prototypes, One Goal: Reusability

Three structural experiments were conducted:

1. Head joints between two bricks using different composite recipes (fungal-only vs. fungal-bacterial).

2. A stack of four bricks using the co-cultivated binder.

3. A full-scale wall prototype, built from 100 reclaimed bricks sourced from two Danish demolition sites.

   
   

Reclaimed clay bricks, bound together with mycelium-bacteria based composite. Image credits: Hyun-Kieffer & al.

All experiments used lime mortar-era bricks that were cleaned and treated with boiling water or heat to reduce contamination. The co-cultivated mix ("compB") showed slightly stronger adhesion (0.05 MPa) than the fungal-only mix (0.044 MPa), comparable to conventional hydraulic lime mortars. Despite the fragile nature of the fresh composite, once dried, the material formed a stable, removable bond.

Construction Meets Biology

The wall prototype was grown over several weeks at room temperature. Heating blankets were used to maintain optimal microbial activity when temperatures dipped below 24°C. While some microbial contamination occurred, it did not significantly affect the performance of the intended species. Spraying the structure with a urea and calcium chloride solution further enhanced mineralisation and stability.

 Stack of four bricks and wall fragment prototype. Image credits: Hyun-Kieffer & al.

This approach mirrors the principles of kintsugi—repairing broken ceramics with visible, meaningful materials. Here, the visible microbial growth becomes both structural and symbolic: a regenerative scar that binds reclaimed parts into a whole.

A Path Toward Circular Masonry

This research suggests microbial mortar could one day enable easier dismantling, repair, and reuse of bricks—a shift from permanent adhesion to purposeful impermanence. With more development, prefabricated microbial-bound masonry elements could become viable, especially where speed and scalability are less critical.

Future work is needed to test long-term durability, weather resistance, and real-world performance. But as a proof of concept, it’s a compelling case for building with biology.