Abstract and purpose
The collapse of the European wool value chain—processing shifted east, traditional breeds producing coarse, low‑value fibre, and raw fleece often classed as waste—coincides with a crisis in ceiling construction: high embodied carbon, linear material flows, and aesthetic loss. This thesis proposes CatVa: a prefabricated compressed earth–grog block reinforced with directionally aligned waste wool fibres, designed as a mono‑material, circular ceiling module inspired by the Catalan vault. CatVa aims to match the vault’s compression logic while adding ductile, crack‑bridging behaviour and cutting embodied carbon by roughly 60%.
Context and motivation
Wool, once central to European rural economies, is now often burned or discarded due to market collapse and regulatory barriers; this threatens shepherding and landscape stewardship. Meanwhile, the thin, efficient Catalan vault—a compression shell with low material use and high spatial quality—has been displaced by concrete slabs that emit far more CO₂. Linking these crises, CatVa diverts local waste wool and demolition grog into a reuse pathway that revives compression‑based vault logic in a prefabricated, thermally active ceiling element.
Design hypothesis
The core hypothesis is that an unstabilised earth–grog block (local clay binder + crushed fired‑brick grog) with thin, directionally felted wool sheets placed along principal stress trajectories can reproduce the Catalan vault’s load path while introducing ductility and enabling circular end‑of‑life options (reuse, crushing to grog, or biodegradation). Directional felting exploits wool’s crimp and scale structure to mechanically interlock with the clay matrix, yielding post‑peak residual capacity absent in plain rammed earth.
Methods — mixed, iterative approach
Research combined contextual interviews, iterative material testing, digital thrust‑line form‑finding, and full‑scale prototyping. Qualitative work engaged shepherds and a local carding factory to secure first carded webs (thin, aligned wool sheets) and contextual knowledge. Quantitative testing produced over 40 specimens assessed by compression (100 × 100 × 100 mm cubes) and three‑point bending, varying earth:grog ratios, wool dosage (0–1.2 wt%), fibre types, felting method, and moisture. Thrust Network Analysis (TNA) in Grasshopper guided geometry so thrust lines remained inside the brick cross‑section. Fabrication progressed from small models to A3 modules (≈600 × 420 mm, ~25 kg) produced in CNC‑milled plywood/CLT moulds at Valldaura Labs.
Materials and fabrication innovations
All inputs were local: Valldaura clay‑rich earth, demolition grog, and waste wool carded in Sabadell. A custom felting needle tool and a modified drill‑hammer compaction plate (producing a beneficial vibration effect) were developed to embed and interlock fibres through successive lifts. Wool sheets were layered at alternating orientations and driven into the matrix to create a 3‑D interconnected fibre network rather than random short‑fibre dispersion.
Key results
Optimal mix: 40% earth : 60% grog : 0.5% wool (by weight), ~12–16% water, yielding good workability, <0.5% shrinkage, and densities of 1700–2000 kg/m³. Compression: wool‑felted specimens consistently reached ~2.5–3.5 MPa, sufficient for vault service loads (<<1 MPa) with a safety margin. Flexure: three‑point bending showed substantial gains—best specimens reached ~0.5–0.9 MPa flexural strength and retained 13–18% residual load post‑peak, demonstrating ductile, crack‑bridging behaviour. Directional felting outperformed random fibre dispersion: comparable toughness gains were achieved at lower wool dosage. The full‑scale A3 module supported informal live load tests (a standing person) after drying, and TNA confirmed compression‑only equilibrium for the proposed vault geometry.
Environmental and hygrothermal performance
Avoiding firing and cement, and using local waste streams, yields an estimated embodied carbon of ~100 kgCO₂/m²—around 60–80% lower than typical concrete ceilings (300–500 kgCO₂/m²). The wool–earth–grog composite combines hygroscopic buffering (enhanced moisture sorption vs concrete) with thermal mass, making the module suitable for Thermally Activated Building Systems (TABS) by integrating PEX tubing voids into the brick. This positions CatVa as both structural and climate‑regulating.
Comparative advantages and limitations
Compared with unreinforced earth, CatVa adds ductility and residual strength; compared with concrete and cement‑stabilised earthen systems, CatVa offers superior circularity, biodegradability, and lower embodied carbon though lower absolute strength. Limitations include modest compressive strength relative to cementitious materials, vulnerability to prolonged wet‑dry cycling, labor‑intensive fabrication, drying times (14–28 days), and the need for Eurocode‑level structural certification for seismic and overload scenarios. Wool dosage is limited (<0.5 wt%) to avoid clumping that induces voids.
Unexpected findings and practical insights
Three notable outcomes emerged: (1) directional felting produced a true 3‑D interlock, improving flexural toughness by roughly 35% over chopped fibres; (2) the drill‑hammer compaction unexpectedly improved density and potentially fibre alignment; (3) preliminary observations indicate higher hygroscopic buffering than anticipated, enhancing condensation control and thermal comfort potential. These findings highlight that low‑tech fabrication innovations can meaningfully improve material performance.
Socio‑territorial impacts and scaling
The project acts as a node of knowledge circulation—research, shepherding, carding industry, craftspeople, and students collaborated—and demonstrates a bio‑regional production model (materials sourced within ~15 km). Potential scale‑up models include mobile production near demolition sites, local grog and wool hubs, and community fabrication workshops. This could create new income for shepherds, demand for local carding, and circular supply chains for demolition waste.
Conclusions and next steps
CatVa validates the central hypothesis: directionally felted wool in unstabilised earth–grog blocks enables a prefabricated, catalytic vault system that revives compression logic, introduces ductility, and drastically reduces embodied carbon while maintaining circular end‑of‑life options. Future work should pursue hydraulic press production for uniform density, FEM certification for structural codes, quantitative thermal and durability testing (TABS flux, freeze‑thaw, fungal resistance), and live‑load testing on full installations. If scaled thoughtfully, CatVa presents a pathway for transforming waste wool and demolition grog into climate‑resilient, culturally resonant ceiling infrastructure.
