Cob:

Cob is another time-tested earthen building technique used primarily in England and other parts of Great Britian. Pieces of “cob” are made by mixing clay-rich mud, long straw fiber, and sand, pressed into each other forming a monolithic structure. The pieces of “cob” dry together into one cob wall instead of drying separately as do adobe bricks.

Benefits:

• Good for wet climates where drying adobe bricks would not be feasible
• Forms thick strong walls
• Can make very organic shapes as are not limited by any form
• Great thermal mass

Building:

To make pieces of “cob”:

Make a mud mix similar to the adobe mix described above but with less water to make a thicker consistency. Instead of adding rice husk, add long straw (and maybe sand if your clay is too sticky). Mix with your feet either in a pit or on a tarp. Make the mix thin enough so that you can work with it easily but thick enough so that it still holds shape.

Take out pieces of this mix and make something similar to a small loaf of bread. Kneed this into a foundation already laid. Interlock these cob loaves by laying them in opposite directions for each layer. You can use a dull stick to sew the pieces into one another.

You can only build so far in one day depending on how wet your mix is as to not let the walls slump with holding themselves up. You may be able to build 1-2 feet or up to 1 meter in one day. When you see the wall have a tendency to slump you know you have gone high enough.

Although at Pun Pun we don’t use cob technique in building up whole structures due to the amount of time it takes to build, we use cob often in making benches, furniture, relief sculpture, and as a joint material for putting in windows, doors, sealing on roof beams, sealing open spaces, etc.