Building with cob is really easy. Anyone can learn in a few minutes and it just takes a bit of guidance as you go up the wall to make sure everything is on track.
First up, for your first layer you are going to need a bucket of clay slip. This is made with filtered clay and water. When it is a nice pastey consistency you can use it to paint on to the stone foundation. It doesnt have to be an exact consitency, just whatever feels nice to paint with and sticks to the wall well. The slip is used to bind the cob to the wall.
Next you need to take some cob and push it right in to the top of the wall. Cover the whole top surface and really push it into the gaps. This will not only hold your cob wall to the foundations but will also serve to really strengthen your top layer of rock. Do not build down over the side of the rock as this thin piece of cob will be very weak and will eventually break.
At the edges of your wall make sure to keep an eye on your vertical and horizontal lines. Your horizontal line should be straight, and not necessarily following the lines of the stones as they will be more uneven. Your wall should protrude a little from the stone wall and then go straight up. The protrustion is to allow any rain running off the wall to drop infront of the house rather than running in to the stone wall.
Once you have covered the section you are working on with a small layer of cob you can start building up. You can take massive lumps of cob and spread them in to your wall, just really make sure you merge the layers in well. You can usea stick with a blunt end if you like, or use your fingers and thumbs. It is really important to integrate the layers or when the cob dries it will start to seperate in to the lumps you have made.
Keep going up. Pretty soon you will need benches and scaffolding to keep going as you are going to hurt your shoulders working too high up.
You can move your cob around in wheelbarrows and buckets, but a really easy method is to make balls and throw them along a line, with the last person placing them on the wall.
After you have finished a raise (recommended not to go up more than 60cm in a day) you can cover your wall to protect it from the rain, or in our case, stop water from evaporating too quickly and drying the wall so it is still soft when we start again.
As you go up your wall you need to remember to instal your dead men which will provide a wooden surface for your doors and maybe windows to screw into. Use a spirit level to make sure the dead man is in line with the base of the door, or in line with the stone that sticks out the furthest from your foundation wall.
If you built your window frames in advance you will also want to keep an eye on the height of your cob in order to set your windows in at the right time.
If you plan to build your electric tubes in to the wall then you also need to remember what height your plugs will be and remember to put the tubes in at around this height.
Your walls will probably start to bulge at some points so you can either bash them back into place, or cut them with a modified saw like this, then you can put the cob back on top of the wall after cutting it from the sides. Just make sure to cut when the wall is still a bit wet.
The best thing to do is get out there and try it. The most important thing to remember to create a strong wall is to integrate the layers you are putting on to the wall.
After building, whilst the cob is still wet you can stab lots of holes in the sides of the walls to make sure that the centre dries well.
Good luck and have fun
2 Comments Add yours
Mother Earth News article and this one have NO definition of what “cob” is or how one makes it.
Do not assume people automatically understand what you’re talking about!
What do you mean Mother Earth News?
This is a post about how to build with cob. If you want to know how to make cob, go and find the post describing exactly that.