Introduction: Recycle Plastic Into Giant Lego

About: Hey! I'm Henri and I love making things

Hello, and welcome to my instructable about plastic recycling. This project is the result of a course I studied at university called "Architectural Technology Research". The brief was to investigate any part of architectural technology that interested you and produce a research document. I chose to look at citizen lead plastic recycling and how it might empower self builders, particularly in countries where low-cost housing is required and there is widespread poverty.

The process is inspired by a really amazing design studio called Studio Swine and in particular their project Sea Chair. In this project plastic is recovered from the sea, melted and moulded into simple pieces that are assembled to make a beautiful piece of furniture whilst raising the issue of marine pollution. Sea Chair is an open source project, the information required to replicate the project is freely available, from how to build your own furnace safely to the sizing of the mould pieces to make the stool.

I decided to take their method and apply it to my own project. This project was very much an experiment into the possibility of whether citizen lead plastic recycling is viable in developing countries where perhaps recycling is not yet a priority. My project was also influenced by the work of Conceptos Plásticos, a company in Columbia currently building low-cost housing, from waste plastic, for those most in need.

I thought I would share the results not necessarily so that someone might recreate this project like for like. If you are wanting to make enough giant lego from recycled plastic to make anything think again! It is intended more as reference material, to share my research into the behaviour and scope of the material.

Step 1: The Mould: Design

To begin with I thought about how I would shape the molten plastic into a brick shape. I also of course had to think about the shape of the brick, the Lego shape was preferable in the context of the research project since it enables quick and easy assembly without the need of mortar.

The mould I designed is a simple press that comes apart to allow the brick, once cooled, to be freed. It was also intended that no specialist equipment or materials were used in the process to enable it to be replicated regardless of location.

The brick's dimensions match that of a standard British brick: 65 x 102.5 x 215 mm

Step 2: The Mould: Fabrication

The tools I used in the fabrication of the mould:

  • Donkey saw
  • Pillar drill
  • Drill bit 6mmØ
  • Hole saw 50mmØCu
  • MIG welder
  • Panel saw
  • Metal Guillotine

The material used in the fabrication of the mould:

  • 2.4m of 20 x 20mm steel square section
  • 220 x 300mm of 18mm plywood
  • 400mm x 300mm of 2mm thick steel plate
  • 200mm of 20 x 20mm steel L profile
  • 100mm of 50mmØ steel pipe
  • M6 nuts and bolts
  • Black spray paint
  • Red spray paint

Step 3: The Furnace

The furnace I used was based on the Studio Swine method. It is simply a large cooking pan with a tin filled with charcoal bolted to the lid. Holes are drilled through the tin and the lid to allow the noxious fumes to pass up through the charcoal, this works as a basic filter. A hole is also drilled in the lid for a thermometer to be placed. The furnace should then be wrapped in fibre glass insulation and a layer of aluminium foil.

Step 4: Collect Your Material

To make just one brick I collected a lot of plastic, 1.3kg of clean recyclable plastic chopped up into 1 x 1 cm squares. It is important to use particular plastic types, not all are suitable for this process. I collected High Density Polyethylene (HDPE #2) and Polypropylene (PP #5). The reason for this is their lower melting point of around 130ºC. This makes it a little safer and easier.

I collected the vast majority of what I melted at home and it took about 3 weeks to collect what I needed. I also put a bag in my communal stairwell with a sign asking for my neighbours plastic.

The Sea Chair project appeals for people to go out to the beach and collect plastic that has been washed up. Whilst I like the sentiment it would take an incredible amount of time to collect 1.3kg, also it would be difficult to identify which plastic types were collected.

Step 5: Melt Your Plastic


Melting plastic is potentially very dangerous. You are dealing with high temperatures and nasty fumes. If molten plastic gets onto your skin it will be very painful and difficult to get off. Make sure to cover all skin, wear safety goggles and a respirator. Also it is essential to do this outside. I went to the beach.

The process is pretty self explanatory. Heat the plastic pieces over a camping stove until you reach 130ºC, be careful not to burn the plastic an occasional stir should help with this.

I imagined the plastic would flow a bit when heated to melting point but I found it to be more the consistency of dough (perhaps I should have heated it to a higher temperature) As such I had to scoop the plastic out of the pan and into the mould.

Once the mould was filled I clamped it shut and pushed more plastic in through the top and pressed it in with the handle. This all has to be done very quickly, before the plastic cools.

Step 6: Results

Once the plastic has cooled you should be able to remove the brick from the mould. Easier said than done! It took considerable force to remove the brick and I actually had to cut the mould apart to release it.

I am pretty pleased with the result though. The brick is very tough and I like the aesthetic of the swirling plastic colours, although not sure I would want a whole house built from these bricks!

The conclusion of my project was that it would in fact not be a suitable process at a citizen level, this kind of recycling needs to be done at scale because of the quantities of plastic needed.

I really enjoyed the project and I think recycling your own plastic waste is something that can work, just not for building giant lego bricks. Precious Plastic is a dutch designer who has built a series of open source machines that enable home recycling and the results are amazing, the machines however require serious metal working skills and quite a bit of money to build.

I hope you have found this instructable to be interesting. If you have any questions please leave a comment. Happy making!

Trash to Treasure Contest 2017

Participated in the
Trash to Treasure Contest 2017