In the seven years I’ve run The Year of Mud and written about building with cob, I realize I haven’t written a simple ‘how to mix cob’ post. For many folks, particularly anyone coming across my various cob oven articles online, it may not actually be obvious how you mix cob, whether it’s for an oven, bench, building a house, etc. So, better late than never — here is a handy reference if you want to mix the perfect batch of cob for your project!
Cob, cobb, or clom (in Wales) is a natural building material made from subsoil, water, fibrous organic material (typically straw), and sometimes lime. The contents of subsoil vary, and if it does not contain the right mixture, it can be modified with sand or clay.
Some Straw, Not Too Much Nor Too Little
I have never measured straw in any particular fashion. Straw is strictly “to taste”, and can be varied depending on what application you’re using the cob for. Though more often than not, you’ll want a fairly rich addition of straw — enough that each handful of cob has long strands running through it, but not so much that the cob is difficult to work with. Sprinkle it in bit by bit.
And don’t forget — straw should be absolutely dry, and free of mold and decay! Straw from wheat, rice, oats, or other common grains are all acceptable.
If you slake your clay as I mention above, you may want to pour off any excess water before dumping the clay into your pile of sand. It’s much easier to add water than to take away. The cob should never be difficult to mix… it will take a bit of time, probably 10-15 minutes of stomping with some experience, and the clay and sand should incorporate easily. If it’s not, add some water a bit at a time.
Building with Cob: How to Mix Cob
Let’s try to keep this basic and to the point. Cob is the simple combination of sand, clay, straw, and water. The proportions of these ingredients will greatly affect the strength, sculptability, and ease of use of this timeless natural building material. Depending on where you live, and the type of sand and clay you have access to, you may end up altering this “base recipe” for the perfect batch of cob.
The sand you should look for is coarse, or “sharp” as some building suppliers will refer to it. What you’re after is sand that has a rough texture, not smooth and rounded like beach sand. The sand should “grab” the clay and incorporate easily, and to that effect a range of particle sizes is nice, too.
Fill up a wheelbarrow a few inches shy of the top for a manageable amount to mix.
Clay will be different depending on where you dig it up. To see if you have a good quality clay, use this test to see if the subsoil you’ve sourced has a good clay content. Don’t confuse silt for clay — it needs to be sticky stuff. You don’t need totally, 100% pure clay here — as long as the subsoil is rich in clay (enough to easily pass the rolling test), you’re good to go.
Slake (soak) the clay in buckets or barrels overnight to let it absorb water and be easier to mix. 2 1/2 to 3 full five gallon buckets of clay is typically what I use per one wheelbarrow of sand.
Is Cob the Building Material of the Future?
FAQ
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What is a Cobb salad?
An instant classic, the Cobb is a chopped salad made up of lettuce, hard-boiled eggs, chicken, bacon, avocado, Roquefort cheese (blue cheese is often substituted), tomatoes, and red wine vinaigrette. It is hearty and filling, and a little bit decadent as far as salads go. And yes, it was actually named after a person.
What ingredients are in a Cobb salad?
This Cobb salad has some of my favorite ingredients: chicken, egg, tomatoes, blue cheese, and avocado. This restaurant-worthy Cobb salad recipe, with crunchy lettuce and deliciously filling toppings, is sure to be a hit on any table. What Is a Cobb Salad?
Where did Cobb salad come from?
The original Cobb salad was created in 1937 in Los Angeles, when The Brown Derby restaurant owner Robert Cobb made a late-night snack for his friend Sid Grauman, according to the Institute of Culinary Education (ICE).
How do you make a Cobb salad?
You’ll find the full, step-by-step recipe below — but here’s a brief overview of what you can expect when you make Cobb salad: Boil, peel, and chop the eggs. Cook, drain, and crumble the bacon. Assemble the salad. Drizzle with dressing before serving.