A backyard lab that turns Nairobi's plastic into paving stones
Kenyan engineer Nzambi Matee left her job, set up a lab in her mother's back yard and developed paving blocks made from waste plastic mixed with sand.
The small thing
In 2017 Matee left her job and set up a small laboratory in her mother's back yard in Nairobi to experiment with mixing waste plastic and sand.
The problem
Plastic bags and packaging litter Nairobi's streets, and only around a tenth of plastic in Kenya is recycled, according to Africanews. Kenya banned single-use plastic bags in 2017, but Unbias the News reports the ban has not been fully effective and many other plastics are not covered.
Why Nzambi Matee (Gjenge Makers) started
UNEP reports that Matee, who studied materials science and had worked as an engineer in Kenya's oil industry, was moved to act after routinely seeing plastic bags strewn along Nairobi's streets. She told UNEP she put all her savings into the project in its first year.
What they did
Gjenge Makers shreds plastic waste, mixes it with sand, heats it and compresses it into paving blocks using a locally built machine (Unbias the News). A social entrepreneurship scholarship to the University of Colorado Boulder let her use materials labs to refine the plastic-to-sand ratios (UNEP). The pavers are certified by the Kenya Bureau of Standards, according to UNEP.
The blocks are used on paths, alleys and school grounds; UNEP reported that a skills training centre in Mukuru Kyaba, an informal settlement, laid them where pupils had previously walked on dirt paths.
What changed
UNEP reported production of about 1,500 pavers a day in 2020. Unbias the News reported in 2023 that the company processed 10 to 20 tonnes of plastic waste a month, and Africanews reported 50 tonnes recycled in 2021 and more than 100 direct and indirect jobs. Claims that the pavers are stronger and cheaper than concrete come from the company and, as Unbias the News notes, have not been independently verified. Matee was named a UNEP Young Champion of the Earth in 2020.
What they learned
Matee has said demand is higher than her equipment can meet, and that scaling up from one paver to thousands is the real challenge. She has said she is willing to license the technology so others can use it.
“Plastic is a material that is misused and misunderstood.”Nzambi Matee (Gjenge Makers), as quoted by UN Environment Programme (UNEP)
Copy this idea
Practical guidance written by our editors from the sources below. Adapt it to your place, and check local rules and safety first.
- Problem addressed
- Mixed plastic waste with little recycling market.
- What to do
- Explore turning sorted waste plastic into practical building products, ideally by partnering with an existing producer or licensing a proven process rather than starting from scratch.
- Materials and resources
- Sorted, cleaned plastic; sand; shredder, heating and moulding or pressing equipment.
- Approximate cost
- High
- Skills
- Materials testing, machine building or operation, workplace safety, product certification.
- Time
- Years of development for a new product; Matee's prototyping took around a year and the first full batch longer.
- People needed
- A small technical team, plus waste collectors and buyers.
- Difficulty
- Hard
- Risks and limitations
- Heating plastic can release harmful fumes; work only with proper ventilation, protective equipment and expert advice. Products used in building need testing and certification. Possible microplastic shedding over time is not well studied.
- How to adapt it
- Smaller groups can start by collecting and sorting plastic for an existing recycler or brick-maker.
- Lessons learned
- Get products tested to national standards early, and plan for the jump from making one item to making thousands.
Why it matters
Paving blocks will not absorb all of Nairobi's plastic waste, and the long-term behaviour of plastic-based building materials still needs independent study. But the project shows how locally built machinery and local waste can be turned into a product people need, while creating jobs.
What didn't work
Matee told UNEP the first full batch took years of work, and that she gave up her social life and savings for a year. Neighbours complained about smells from her early experiments, and in 2023 she said demand exceeded her production capacity (Unbias the News).
Editor's note
Most recent independent reporting found (Unbias the News, 2023; Africanews page updated 2024) describes the business as operating. Current output was not independently confirmed for 2025–2026.
Sources: how do we know?
Evidence level: Documented. Supported by reliable published sources such as UN agencies, award bodies and reputable journalism. Not yet independently re-verified by our editors. What the person says and what independent sources establish are attributed separately in the text.
- un agency
Building blocks for a greener Nairobi — UN Environment Programme (UNEP), 15 December 2020Supports: 2017 backyard lab; background in materials science and oil industry; inspired by plastic on Nairobi streets; Colorado scholarship; KEBS certification; 1,500 pavers a day; Mukuru school; Young Champion of the Earth 2020; quotes. - reputable journalism
Can plastic bricks pave a road out of Kenya's plastic waste problem? — Kimani Chege, Unbias the News, 10 March 2023Supports: Process; 10–20 tonnes of plastic a month; strength claims not independently verified; neighbour complaints; capacity below demand; willingness to license; Kenya bag ban context. - reputable journalism
Kenyan women turn plastic waste into bricks stronger than concrete — Doloresz Katanich, Africanews (with AP), 16 December 2020Supports: Around 10% of plastic recycled in Kenya; 50 tonnes recycled in 2021; over 100 direct and indirect jobs; bricks used on Nairobi sidewalks.