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Plaster works: transforming local waste into purposeful objects

Updated: Feb 14, 2022

By Gareth Owen Lloyd

Photo: Plaster bowl released from wood turned bowl © Paul Cochrane

In 2021 CIRCuIT partner Clear Village invited GoodWaste, a London-based design studio breathing life into discarded materials, to join them in a three-month hackathon, Urban Mined, with the aim to find diamonds in the rough from London’s demolition waste.

Urban Mined researched demolition materials, investigated how well they are accounted for and explored potential interventions. The team decided to focus on deleterious and contaminated materials as these have the least value and are problematic to dispose of. Deleterious materials in buildings (such as asbestos) are considered dangerous if removed and are banned from being used in new buildings.

A visit to EMR metal recyclers
Photo: A visit to EMR metal recyclers © Clear Village

It surprised the hackathon researchers just how much material is reclaimed. After visiting a European Metal Recycling (EMR) metal recyclers site in London they were impressed how efficient the system can be when there is a market for a material. Unfortunately many other materials easily lose value when contaminated.

This was apparent particularly with two materials: glass and plasterboard. Glass goes through an energy intensive process before being installed in buildings but then is often broken on removal and gets crushed down and turned into cheap aggregate filler for concrete.

Photos: Close up of glass aggregate sample and plaster waste from Roy Hatfield Ltd © Clear Village

Ubiquitous and hidden in most walls, plasterboard is broken when pulled out and is considered contaminated from installation with screws, wood, metal joists and layers of paint.

Gypsum: a diamond in the rough?

Photo: Decalcified plaster © Rafael El Baz

The Urban Mined team connected with Roy Hatfield Ltd, who collects, processes and remanufactures plasterboard for purposes such as agriculture. When correctly recycled in this way, plaster is safe and non-toxic, but if mixed with bio-waste it gives off ‘stink gas’, a noxious gas and potential explosion risk in landfill.

Gypsum is the main constituent in many forms of plaster, blackboard/sidewalk chalk, and drywall. It has two main sources: as a mineral mined from the earth, distinguishable in the UK by its pink tone and a white synthetic gypsum, produced as a by-product from the flue-gas desulfurisation process from fossil fuel power stations. The gradual closure of many coal-fired and fossil fuel power stations mark a return to damaging gypsum mining and the need is greater than ever for plaster recycling to make better use of the minerals already in circulation.

Roy Hatfield Ltd, who have been recycling plasterboard for decades, face the challenge of an under-developed market for reprocessed gypsum. In response, the hackathon explored how the qualities of reprocessed gypsum can be celebrated and reimagined it as a luxury material that could be reintroduced to our homes without hiding it under layers of paint.

Uncovering plaster’s circularity

Photos: Fused glass in a plaster mold and samples on display © Clear Village

Plaster has the capacity to be a circular material - with a small amount of heat it can be decalcified and reversed back to its original state. Discovering this during the hackathon was a kind of eureka moment. Mixed with water and left to set, the recycled plaster was used to produce a set of molds which held crushed glass for melting in a fusing kiln.

Urban Mined started researching and testing historical plaster-based processes such as scagliola (imitation marble or other stone, made of plaster mixed with glue and dyes which is then painted or polished), a technique found in 9th century Islamic architecture to the Palace of Versailles. In scagliola the imperfections of the contaminated plaster become a characterful patina when dyed with natural pigments then rippled together to create a marbled effect.

Hackathon turned real life solution

Photos © Rafael El Baz and © Paul Cochrane

The hackathon ended with an exhibition of tests and samples and subsequently GoodWaste was invited by Waltham Forest Council & Arts Council England to scale the process for a full interior refurbishment in collaboration with Blackhorse Workshop.

GoodWaste sourced plaster from local residents and businesses, scaling up the scagliola process using local waste plasterboard, brick dust and ash to renovate a disused high street store in Chingford to become a place where local residents could participate in community workshops teaching sustainability and making.

The difference between the hackathon and refurbishing the space was the sheer quantity of material and processing power that was needed. The technique went from using a small convection oven and pestle and mortar to needing an industrial oven and repurposed corn mill.

First, the process was used by GoodWaste to refurbish the building with a set of bespoke plaster-based furniture and wall hangings. Following this, the plaster process was adapted to become a simple workshop activity that allowed participants to walk away with a final object. 2,000 people visited to make small bowls cast in wood turned molds.

Raw sheets of plasterboard went directly into an oven where the glue melted, separating the paper from the plaster and decalcifying it at the same time. The weakened sheets were then powdered in a crusher ready for participants to mix with local brick and charcoal pigments to be set into a wooden bowl mold.

Project of the future

The future for this project could be to open source the process for others to try. Conversations about waste mostly consider value in terms of its usefulness. But when a designer or member of the public processes, plays with and repurposes a material, it adds a cultural and emotional value. Instead of buying new we can imbue buildings with an aura of place and a narrative that ‘new’ simply cannot.

Plaster Works participants © Paul Cochrane

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