Cob homes are a trend that is taking the world by the storm. They are sustainable, affordable, and they are easy on the eyes! Cob style homes require simple materials like clay, sand, and straw. They are mixed together to serve as a building material, the same as bricks.
The right ratio of these materials, in the cob, will give you a sturdy product to build a sturdy home with. Similar techniques of building have been around for over 10,000 years. A cob house construction is produced from natural building materials and therefore has several advantages over the other construction options available.
Cob houses Vs. Heat
Due to their thick walls, these houses are more thermally regulated than regular brick and mortar. In summer, these walls can provide natural insulation from the heat, and in winter, they carry heat later into the nights. As a result, heating costs for the building are a lot lower.
Cob is also a very durable substance when it is suitably sheltered from the rain. A solid cob roof constructionwill protect the walls from extreme weather changes and may last for many, many years. When the house starts displaying signs of damage, you can apply a new coat of the cob.
Simple DIY Cob-Building Technique
Step 1: Build a foundation.
Cob walls are thicker and heavier than the regular walls built from timber. So, before you construct the walls, you need a strong foundation that can support the weight of this type of construction.
Make sure to remove all the vegetation and loose soil from the ground and outline the margins of your cob construction.
To protect the cob from rain, dig a trench that will surround the structure and direct the water away from the cob. Use compacted gravel to backfill the trench.
Stone and reclaimed concrete chunks are the perfect materials for a foundation. Set the stones on a level, firm ground inside the gravel-trench margin. You are done when the foundation material is solid under your feet.
Step 2: Prepare the cob mixture.
Cob is a mix of roughly 1 part clay, 1 part straw, and 4 parts sand. You can get powdered clay and sand from any local supply store.
Money-Saving Tip: Most soil is a combination of some clay, some sand, and some other materials.
If you are buying it, ask your supplier for ‘compactable fill’ or ‘road base’ to get a more suitable ratio. The ‘soil’ referred to here is not the rich black or red soils found in your gardens, but a type of subsoil with little to no organic matter present in it.
Break up the soil manually and soak it in, for at least a night, sufficient water to give it a pudding-like texture. Pudding is a lot easier to mix with sand than lumps of clay.
Mixing cob with your feet is not only the most efficient way to do it, but it can also be a fun activity!
Pour a bucket of sand in the center of a tarp, a bucket of wet clay over that. Then add another bucket of sand at the top.
Blend the sand and clay to form a pile, keep adding 2 more buckets of sand as you go. Sprinkle the straw over your pile. Use the tarp to flip and blend it till the straw is evenly mixed throughout the sand sand-clay mixture.
Step 3: Start building the cob house.
‘Cobs’ are balls of the above mixture. Break the compound up in manageable sizes – generally the size of a cricket ball or a baseball.
Make some test ‘balls’ and let them dry for about a week, to make sure the structure can stand. Place wet cobs on top of each other in the desired structure and smash them together to form a single unit.
Build a cob wall by placing an inside-facing layer and another outside-facing layer, meld them together to form one unit.
Use your thumbs to weave the stray layers of one cob with another cob. Wet the surface of the cobs before applying a new layer.
Step 4: Apply Plaster to the cob walls.
To finish the structure and give it a polished look, apply plaster in at least two layers. The first coat to mask any imperfections, and a final layer to give it a refined look. The last layer can be improved by using linseed or hemp oil for polish.
Apply the plaster on a slightly damp surface with a firm pushing action. Plasters might crack at the point where you stopped or started, so pick a careful starting and ending point. Apply numerous layers of oil to seal the plaster in.
Step 5: Seal the floors.
The ideal method to finish the floor is to apply several layers of mud and plaster. Follow that with a few coats of linseed oil, applied directly to the mud floor. Use beeswax as the final coat to polish the surface of the ground.
Step 6: Maintain the cob construction.
Store the surplus plaster in sealed jars for future repairs. You can also use oil or sandpapers to fix scratches on the surfaces. Larger cracks will need to be filled rather than plastered over.
Windows in a cob house
Use solid timber as a header for the doors and windows. Use a block of wood, at least 6 inches thick and that can span the width of the wall. The header should fit across the gap of the opening and then extend at least a foot on both sides so that it rests securely on the wall.
Built-In Shelves and Stairs
Because the cob is a flexible material, it can be arranged and molded to give you steps on the floor and shelves in the wall. You can build around specific appliances as required. You can even create curves into the surface and add decorative elements to your structure.
Now, as with everything, here are some cob pros and cons you need to consider, especially if the building is to be your forever tiny home.
Cob Construction Pros:
- Utilizes local, usually inexpensive material.
- You can add creative, delicate details.
- Nontoxic and has a negligible environmental impact.
- High thermal mass aids insulation and temperatures remain steady and comfortable.
- Works well with other natural materials (stone, lime, wood).
- It is earthquake-resistant.
- Build it properly and it will endure for years.
- It resists both termites and fire.
Cob Construction Cons:
- The construction is labor-intensive (although that could be a ‘pro’ if you want to get fit).
- Needs supplementary insulation in colder weather.
- It is unfamiliar to Building Code officials and insurers.
Building cob houses might be a new trend in the construction world, but it is an old method that has been around for centuries. I hope this article will help you make an informed choice when building your dream home.