Ecobricks, Bottles, and Cob Construction
Building with cob, ecobricks and bottles is simple, inexpensive and fun. With enough ecobricks, you can build anything from a simple garden bench to a home using your locally available earthen materials. “Cob” is an ancient natural building technique found around the world in different forms: adobe, wattle and daub, etc. It has been used to build everything from houses, to temples to castles– many of which have endured centuries. Cob not only makes enduring beautiful and highly functional structures, but it works awesome with ecobricks and bottles. We’ve worked hard to develop a simple Ecobrick and cob technique so that adults and students alike can do the work using local organic resources. Follow the steps below. Click to expand.
The easiest ecobrick cob application are benches, gardens and playgrounds. This is a great way to get started with a non-structural, no-risk experience! The technique can be used of course to make walls and homes– just as in the past it was used to be temples and castles.
The simplest applicatin is to lay Ecobricks horizontally in cob mortar. The result is a thick, sturdy construction. The cob mortar must cover all the ecobrick to protect it from UV sunlight (with the optional exception of the cap’s surface and colored bottom of the Ecobrick). Thus protected from UV rays and the elements the brick will last pretty much forever.
Click to expand the steps below for building a simple cob bench.
What's Best to Build?
We recommend starting small with your first ecobrick build. Gardens are ideal! In so doing, you can put our ecobricks to use, involve everyone in the construction, minimize costs (no need for engineers) and learn the core principles of cob construction through experience.
Fact is, Ecobricks make beautiful gardens where we can sit, play and eat. We call them Food Forest Play Parks. Given that most of the plastic we stuff into our ecobricks comes from food packaging, building gardens that grow non-packed food, is pretty apt! This space are created by curving lines of bottles that are laid horizontally. The resulting mini-walls, make great benches and garden bedding walls. Oh… and you can run around and play tag on them too!
Food Forest Play parks are ideal for schools. Teaching children to grow their own food is categorically the most valuable skill we can impart to the next generation. Self-sufficient personal and community food production (as opposed to giant mono-crops) is essential for preserving the Earth’s biosphere. Because cob building is so low cost, and the technique below so easy, students and youth groups can take charge of the full project– from making the ecobricks, to designing the space, to building it. This creates a sense of pride and ownership that is hugely empowering. Best f all, the cob technique you will learn is indefinitely scalable– these are the same fundamentals used to construct houses and buildings.
1. Soil test
The first step is to test the earth that you will use for your construction. Choose and earth with a high clay content. This means it sticks together when you squeeze it. Of course, the earth is different everywhere! Thus, to start we want to figure out the best combination of sand and clay to use for the rest of your construction.
With your chosen earth, make some pancakes! That‘ right, mix small
quantities of cob with varying ratios of your local sand and clay (don‘t bother with the binder for this). Make pancakes of about 3cm by 15cm. Try different rations, like one part sand, two parts clay. Lay out a mix of different rations (i.e. 1:0, 0:1, 1:3, 1:1, 3:1) on a board. Let them dry in the sun and out of the rain. After two or three days review your pancakes. Choose the ratio
that doesn‘t easily crumble, nor which hasn’t cracked. Once you have found the most sturdy ratio, you’re ready to apply this on a larger scale.
2. Setup a safe working area.
Got your site chosen? Clear the space where you will be working of all hazards. Make sure that there is plenty of free space to work and move. Allocate a space for mixing the cob, for piling materials, and for tools. Make sure there are no hazards on the ground for when you get started.
3. Plan and lay your draft foundation
Lay out your ecobricks on the ground to sculpt the footprint of your construction. This will help you determine the curves and shape as well as how many ecobricks you will need. Adjust as you see fit.
4. Dig out your foundation
Once you’ve got your bench line figured out, mark with sticks, then remove your draft bottles. In their places dig a trench 10 cm deep. Pack firm. Fill this trench with medium sized stones.
5. Lay the cement foundation
Mix a rough cement mixture at 1 part cement : 10 parts sand/gravel. We often use up our broken bottles for this mixture– we crush up the bottles and add it as part of the gravel/sand. Pour this over top of the stones. Allow for 5 centemeters of cement above the rock tops.
6. Lay the Ecobricks down
Lay the ecobricks (those you used for your draft foundation) into the concrete. Ensure that only a maximum of 75% of the bottle is covered. Let the cement dry.
7. Mash your cob mixture
Mix your cob to the ratio that you discovered was best in Step 1. Use buckets to measure each part. Dump the buckets of sand and clay onto a large tarp. Add your organic binder (straw, hay, coconut fiber, etc…). Use your feet to mash and mix the cob. Add small quantities of water as you go to help the mixing (but not too much or your mix will be too soupy).
8. Make Cob Balls
You will know that the mixture is complete when you can no longer see any sand and the entire batch is of the same consistency. Have your team make balls out of the mix– this is a last step in the mixing and compaction of the batch.
9. Lay the second layer of Ecobricks
Bring the balls over to the construction. Bang them down onto the concrete layer. Cover with a layer of compacted cob approxamitely 5cm high. Then, lay your next row of bottles. Lay each bottle in between the two below it.
10. Apply more layers of cob
Once the bottles are snug in the lower cob layer, fill in any large gaps between bottles (i.e. on curves) with stones. This will help your cob mixture go further. Fill in with cob between the bottles. Add another layer of 5cm on top of the bottles.
Keep adding layers of bottles and cob! We find that benches are good with two or three layers of bottles. For walls, add a row of iron bar at every 5th layer of bottles.
11. Apply the outer protective coating
The Outer Skin: There are many ways to render or cover your cob mixture to make it strong and water resilient.
- Add cement to your cob ratio so that it is 20% of the mix. Mix in the same way as before. Apply to the outer layer of the
- Paint on a clear acryclic water proofing paint.
- Paint on a layer of fresh cow dung combined with 10% fine clay.
- Paint on a layer of lime render.
12. Finishing the top with cement and broken tiles
For benches you will want to add a layer of cement for sitting upon. Mix cement at 1 part cement : 6 parts sand. Apply at a minimum thickness of 10 cm.
Use broken tiles to make a pattern on your bench top. Lay tile out on a long board first into the desired pattern. Have the pattern ready when laying the cement for the bench top. While the cement is still wet, press the broken tiles half way into cement. Once semi-dry, use a trovel to cover with a layer of fine cement (1:4 mix). Use a wet sponge to continually wipe clean.
Once you are done… plant and enjoy!
Caution! Using cement to build with Ecobricks can cause big problems in the future. When your structure comes to its end and must be moved or broken down, the cement is stronger than the PET plastic. The cement rubble will rupture Ecobricks! This means someone in the future will have a big mess to clean up. It is best minimize the use of cement and maximize the use of cob for your Ecobrick mortar. This way, Ecobricks can be safely removed and reused. Over and over again!
Comment using Facebook
Ecobrick cob constructions are fueled by the magic of collaboration. Projects will require hundreds of ecobricks. Invite and inspire everyone in the community to partake in your green vision! With one clear green space vision, the entire student body, the parents and the teachers can unite. With everyone submitting one or two ecobricks you’ll be ready to build in no time. With many volunteers on hand to mash mud, you’ll be able to construct in no time!