In buildings, the main role of a wall is to support the roof and floor and provide protection from the weather. To build a wall, we have to layer several materials - like making a sandwich or a burger.
The external walls of a building are usually built of brick (damp-proof), and the internal walls are made of concrete mortar with plasterboard, decorated with paint or wallpaper. In modern buildings, there is usually a gap between the two (so that humidity can escape, or prevent it from coming in), and this gap is a spongy insulating material used to retain heat. Especially in colder countries, walls need to hold as much heat as possible for energy efficiency.
Bird's Nest-style brick
In 2019, a developer developed a 3D-printed brick made from household plastic waste. The idea for this brick came from an unexpected place - the nest of the Southeast Asian Baja weaver bird.
This beautiful yellow grassland dweller is known for its elaborately woven houses. The male uses his claws and beak to weave soft grass stems and palm fronds into a hat-like shape. The top section is larger where the eggs will be placed, and below is a slender tunnel-like entrance. The woven structure of the nest protects the eggs from wind, rain and hot sun during incubation.
The developers tried to make a brick in a similar way. Instead of using plant fibers, they wove plastic yarn or thread. First, they used discarded plastic water bottles to shred thin sheets of plastic to make yarn. Then we loaded the yarn into a 3D printer. The printer melts the yarn and then uses a tapered nozzle to deposit the melted plastic exactly where they want it. Think of it like frosting a cake with your best laminating skills. They programmed this printer to crisscross the melted plastic to form a lattice or mesh pattern. Then we coat the lattice with a solid outer layer that traps air in the cavity for better insulation.
This brick is strong. Studies have shown that in the walls of a five-story building, they are as strong as ordinary cement mortar bricks. They perform ten times better at insulating walls than traditional clay bricks of the same size.
Life-size Lego
Bricks inspired by woven birds are considered the preferred choice for building materials. But it's not the only brick made from household plastic waste.
There is another model where the plastic is chopped up and ground into a powder. The fine-grained plastic can be easily poured into a brick-shaped mold (just like you would fill an ice cube box with water). The mold is then transferred to a furnace to melt the plastic powder, which is eventually compressed into a solid plastic brick. It reminds us of the Lego our kids play with.
The beauty of making plastic bricks this way is that we can combine different types of plastic - from water bottles and milk cartons to food packaging and bottle caps - as they all melt between 200 and 250 degrees Celsius.
Additionally, they can be easily assembled and interlocked to produce, a wall that looks like a life-size Lego project. Once the wall is built, you can add clay or cement to cover it on both sides, inside and out, which will make the surface smoother.
Bottle House Wall
The cheapest and most ingenious way to make a bottle house wall is to use plastic waste, combined with traditional building materials and agricultural waste.
Researchers at De Montfort University collaborated with local Nigerian entrepreneurs to develop a prototype bottle house. Discarded water bottles were filled with sand or water to form a bottle block strong enough to be used, and then glued together with clay.
One drawback to this method is that it doesn't retain heat. Instead, it reduces the temperature of the building by absorbing sunlight, preventing indoor temperatures from rising. While this is exactly what is needed in countries with tropical climates, the British weather requires more warmth.
As well as needing to adapt materials to the specific location and weather of a building, we also need to be careful with plastics as some emit toxic substances when exposed to UV light and high temperatures. That said, there is actually a lot of research and work to be done in this area.