Finding Clay!

If you are hoping to build a natural home, whether it be with adobe, cob, slip straw, earth bags etc you will need CLAY!

It is an essential binding agent with thermal mass qualities that is normally never too far away just under our feet.

Below is an explanation of how to find it and what to do when you do!

Before you dig; Observe the landscape

There are a few variations of clay and some key areas they like to settle. Before breaking the soil to see whats below take some time to look and think, the landscape will often give indications that there is clay below, here are some good places to start looking;

When there is rain check to see areas that drain the water slowly (create puddles). Clay is very compact so water can not pass through it quickly
Look for areas on the surface which have cracks (especially after a rainy day when the water has evaporated/drained) clays natural characteristic is to swell when it is wet and shrink when it is dry, this shrinking will create cracks
Look for areas where there is a lack of organic matter; due to the density of clay it is hard for many plant roots to penetrate through it, often only hard shrubs and brambles can.
check out areas close to streams and river banks; clay particles are extremely small and they easily get carried to streams and rivers when it rains. if the banks have burst there will be clay found in the flood plans, also check out the banks, especially where the water is slow where the clay can settle

Take into consideration accessibility and disturbances. Extracting a lot of clay will leave a hole in the ground (this can later be filled or made into a pond or greywater system for the house) so you wouldn't want it on a path or in a garden. Also think about how the clay will be moved, try to look as close to the building site as possible and work your way out.

If you are unfortunate enough to find nothing at all, don't give up, there are still options. I would start by contacting local contractors that create terraces, lakes, dams etc and ask if they can tell you if and when they find clay, there is always a possibility they will deliver. Also, ask the community you live in; many people do landscaping at home and they are more than happy if you can come and take this byproduct away.

Now for the fun bit.....DIG!

There are numerous layers to the Earths surface. We want to make sure we remove and preserve the topsoil and only extract the subsoil below.

How to know you are in the sub, not topsoil;

Normally you will need to dig between 5-10 inches (13-25cm)
There should be a change in colour between the 2 layers
There should not be any organic matter in the subsoil - no small roots, insects etc.
Subsoil should have a natural smell, unlike topsoil which often smells of mould/wet grass

Get your hands dirty!

Once you are happy you are in the subsoil bring out about a bucket worth to examine. then we can do some very basic experiments to see if the sample contains clay;

Wet a handful of the sample and begin to play with it; how does it feel? Clay has a very distinctive silky, smooth and sticky characteristic when wet.
Coat your hand with the wet sample then dip it into a bucket of clean water. When you bring your hand up does the sample remain? The more it remains the higher clay content you have found.
Try to make a sausage from some of the moist sample. A high clay subsoil will roll well and when wrapped around your finger will hardly crack.

Shake it!

The jar test is a fun and interesting way to see what the breakdown of your sample is. It will create definition between each element in your sample so you can get a clearer idea of percentages and content.

I would advice doing multiple tests from a variety of different areas. Always lable where the sample came from and always keep some of the raw material to compare and feel later.

Heres how to do a jar test at home;

crush your sample and remove any large stones or organic matter that might have fallen in.
fill a jar around halfway with the sample (I put a little water in the jar first to stop the sample from sticking to the bottom)
Add a teaspoon of table salt or 1/2 teaspoon of dishwashing soap (sounds strange but it helps to break down the particles and gives a better definition)
Add water till nearly full (leave about 1-2cm at the top)
Put some music on and shake the jar for 5-10 mins.
Leave it where it will not be disturbed for 48 hours

Image from waldereducation.org

Evaluating your jar test

It will take around 24-48 hours for the layers in your sample to settle. When they do the largest particles will be at the bottom, this will firstly be any small stones and then a layer of sand.

On top of this will be any silt in the sample and finally, the last layer on top will be the finest of all and this is clay.

If there is any organic matter it will float in the surface.

With this information you can get an idea of the clay content you have and subsequently what you will need to do to use it to build with. Different building methods require different percentages of clay so this knowledge will go a long way in helping you create a perfect mix.

Remember that every handful of soil will be different so don't get too caught up on percentages and ratios.

The best way to learn is to play and gain experience!

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