This used to be done by herding sheep backwards and forwards over the clay. These days asking friends and school children dressed up in Wellington boots and old clothes to help trample the clay is more likely. Kids enjoy puddling the clay learning an almost forgotten skill. Driving a digger, tractor or running a wacker plate over the surface works too. Either way it's a fun and enjoyable and Eco-friendly way to build a pond.
If you are lucky and the hole you are digging is in clay there won't be to much puddling to do. Providing the clay is suitable (I have explained how to test the suitability below) it’s just a case of digging down and around until you have dug out a pond. This can be done by hand with a heavy duty garden spade or a digger.
The clay being dug out can be used to form banks, the higher the bank the less depth you will need to dig. If you are digging the pond into a slope, surplus clay will be needed to raise the bank at the bottom of the slope to end up with a level surface........
If your garden soil is loamy or even sandy you can still build a clay lined pond. Its hard work, but a much better choice for a wildlife friendly pond than using a plastic or rubber liner. And with basic maintenance will last a lot longer.
A couple of things to consider though, puddled clay needs a firm base so you can't site the pond too near the edge of a slope where soil may subside or on silty or peaty soils that are affected by ground water and move causing the puddle clay to cracks and leak. More information lower on this page.
Clay is a natural product and the traditional method of lining ponds and is still the best and certainly the most Eco friendly material for lining garden wildlife ponds and water features. It's spread in layers over the excavation, soaked with water and then each layer is repeatedly trampled to remove all the air. Puddling is hard work and can be fun, but must be done thoroughly to make a waterproof seal.
With the help of friends or the local school, (the kids love it and learn about an almost forgotten skill) it really can be a fun job but if you want to save time or are mostly working alone you can use a tracked digger or a wacker plate to drive back and forth over the layers of clay to speed the process of puddling up.
Positioning the pond.
A clay pond can be dug almost anywhere in your garden except in deep shade or under leafy trees the roots will make digging difficult, and future growth will probably break through the clay. If you have kids, safety will be a important consideration as will access and because you will be planting wildlife cover around the pond visibility should be considered.
Sourcing suitable clay for puddling
If you are lucky and can wait, clay may be available cheaply as a waste product from local building sites and ground work or more likely and I'm afraid more expensive, from clay producers and most suppliers of aggregates.
The puddling clay I use is sourced locally when I can. Otherwise I use the supplier of puddling clay used by British Waterways for lining canals.
The minimum clay content of soil suitable for lining ponds is 60%. I have included a simple way to test for clay below.
How thick does a clay liner need to be.
The clay layer should be at least 8"thick and laid in layers. Once properly puddled, the clay lining remains waterproof indefinitely, provided it remains underwater. Exposed clay dries out and cracks, so is not suitable for steep streams and waterfalls.
These are a few important things to remember when lining a pond with clay.
Digging out and forming a wildlife pond in a garden using existing clay soil
Best position to site natural clay pond in a garden.
A pond dug out of Clay can be positioned almost anywhere providing the clay holds water, try to avoid shady areas and leafy trees because the leaves are a nuisance when they fall and the roots will make digging difficult, and will probably break through the clay. The site should have enough space to provide a natural area around the bank and edge for land living wildlife and a natural habitat for pond life.
Providing the clay is suitable for puddling it’s just a case of digging down and around until you have dug out and shaped a pond. This can be done by hand with a heavy duty garden spade or a digger. The clay being dug out can be used to form banks, the higher the bank the less depth you will need to dig.
If you are digging the pond into a slope, surplus clay will be needed to raise the bank at the bottom of the slope to get a level surface.
Do's and don'ts when constructing a clay lined pond
The ideal minimum clay content of a soil for a leak-proof pond is 60%.
A simple test to find out the type of soil in a garden.
A simple way of testing your garden soil is to take a small amount of wet soil in your hand and knead it into a smooth paste and then roll it about between your hands to form a ball.
Test to find how much clay there is in your soil.
To test your soil, take a sample, let it dry out, then break it up as well as you can before adding it to a container of water. A tall straight-side container (e.g. a spaghetti jar), is best because it’s easy to see the relative amounts of each constituent. Half-fill the container with water, add the soil, then top up with water. Turn it upside down as many times as necessary to get the soil in suspension and then watch the soil settle out.
Most of the larger particles of sand will settle in about 20 minutes, with the fine clay staying in suspension for a long while and any organic matter floating to the surface. Once all the soil has settled, measure the total depth of the soil in the container, plus the amount of organic matter. Then measure the depth of clay particles (ie those that are obviously not sand).
To calculate the amount of clay:
1. Divide the depth of clay by the total depth of all the soil and the organic matter.
2. Multiply the answer by 100 to obtain the percentage of clay.
eg. if there’s a total of 10cm of soil and organic matter, of which 2cm is clay, divide 2 by 10 (=0.2), then multiply by 100 (=20) to obtain the percentage (20%).
A simple test to find the cohesive property, can easily be made. A small quantity of the clay is mixed with water and made into a roll about 1 inch in diameter and 5 to 10 inches long; and if, on being suspended by one end while wet, it does not break, the cohesive strength is ample.
Suppliers of Puddling clay
This person stumbled upon the perfect place to build a natural clay pond.
"I've started digging a pond on heavy clay soil and have now dug down to 2 foot at the deepest. The problem is it keeps filling up with water which then won't drain away. I emptied 20 litres last night and 20 more today.
We've had heavy rain but obviously the water's much deeper than that. It's on a slope of about half a foot - do you think the water is coming down from the surrounding area?
My Mum thinks I've reached the water table but it didn't fill with water as I was digging.
I'm worried about how I'm going to line it when it's so wet and whether the water will then build up under the liner? Any advice appreciated please."