How to make a clay pond

How to puddle clay for lining a clay pond.

Puddling Clay.
There isn't to much that is complicated about puddling clay, just hard messy work. Puddling simply means compacting the clay to completely squeeze the air out of it, leaving a densely packed material which forms a watertight barrier. 
Using a wacker plate to puddle the clay
Using a wacker
Bare foot fun puddling clay
Bare foot fun
Puddling clay
Puddling clay

 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. 

There are two main ways of digging out and making a clay lined pond.

Building a pond in clay soil

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........

Lining a pond in non clay soil with puddled clay

 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. 


How to line a garden pond in non clayey soil using Puddled clay 

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. 

  • The slope of the clay bank should be less than a 30% gradient. This makes it easier to puddle and will help prevents soil placed for planting falling to the bottom.
  • No need to make the pond any deeper in the middle than 1m. This will make it easier to maintain, trim plants and repair the pond.
  • Puddle the clay thoroughly until all air bubbles have been squeezed out. One way of doing this is to tie a whacker plate’ on a rope and let it vibrate down the slope and across the bottom.
  • Keep adding and puddling layers of clay until the clay is at least 20cm (8”) thick all over the walls, bank and bottom. 
  • Clay that is allowed to dry out when the water level drops through evaporation will crack and leak, so a clay lined pond will have to be kept topped up at all times.

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. 

Keep the slope of clay banks to less than 30% gradient to make puddling and planting easier and for pond life to be able to get in and out with ease.   Also the pond doesn't need to be any deeper in the middle than 1m. to make planting and future maintenance easier and safer.
 
The top layer of soil you dig out will probably not contain enough clay particles to make it suitable for puddling and sealing the pond, so store this in an accessible place to spread over the bottom and sides for planting in.
Only use the clay being dug up as you get deeper for lining the hole. Once the hole is dug and any clay you have used for patching is in place, it needs to be kept damp as it will dry out and crack, allowing water to seep through.
Filling and testing the clay pond
With a bit of luck the hole will start to fill naturally, especially if it's raining 
You've now dug the hole out and It's time to turn it into a pond by filling it with water.  If it's raining let it fill naturally.
If you are working in dry weather the exposed clay will dry out and crack up quite quickly so you will have to use tap water if no other source is available.
 
If the pond fills (this is the stage when I Keep my fingers crossed) and the water level stays about the same then success.
If the pond level drops more than a few inches and you can find the leak, dig out the area around the leak to about 8 inches deep and fill it with freshly puddled clay. In hot weather, water evaporates and the water level will drop a bit. During repairs in dry weather It's important to keep exposed areas of clay damp.
  
If the pond empties you have got two choices 
1 Line the whole pond with puddled clay. Having gone this far this would be my preference. 
2 You may have to line the pond with a rubber liner instead.
It's probably a good Idea, (certainly a time saver) to test the suitability of the clay in your garden, I have included some different methods of testing clay further down this page.
But assuming your clay was suitable and your new clay pond is holding water, It's time to spread the surplus soil around and plant with wildflowers to encourage wildlife, particularly bees and butterflies, but also cover for frogs, newts and toads. Plant the banks with wildflower seed mixtures for bees and butterflies and plants for wildlife cover and the marginals that provide cover around the margins and It's time to  Enjoy your pond.

Do's and don'ts when constructing a clay lined pond

  • As with all pond excavations, ensure that you have a level area cut into the ground or on a slope build banks at the lower part of the slope. 
  • The final depth should be 1 metre deep at the deepest point.
  • The slope of the sides should not be more than 30% to make the puddling process and access for pond life easier.
  • The clay should be thoroughly puddled until all air bubbles are squeezed out.
  • The clay used should be uniform in consistency and pliable. .
  • The clay must never be allowed to dry out. Large sheets of plastic can be used to keep the clay damp. If you cant get it all done in one day, do one section completely,
  • Where the clay meets the soil, it is inevitable that capillary seepage will set up and leach water from the pond.
  • To prevent this you can set up a ‘capillary barrier’. It will also function as insurance for keeping the water level high enough above the clay liner to keep moist. This can be set up before you start by excavating a shallow 15cm deep and wide and 30cm below water level around the top of the pool and filling it with a kneaded ring of clay

What percentage of clay is needed in soil used for puddling.

 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. 

  • If its Sticky and gritty its loam.
  • If it easily rolls into a ball and is sticky, workable like Plasticine, stains your skin, can be smoothed and made shiny, and doesn’t crumble its clay.
  • If it wont roll into a ball and feels gritty its sandy soil.
  • If it feels slippery and silky its probably a silty loam.

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%).

 Another test for the suitability of clay for lining a pond 

 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.

 

A test to find the water-retaining properties of clayey soil

  • mix up one cubic yard of clay with water,
  • make it into a plastic mass.
  • make a round hole in the top, large enough to hold a gallon of water.
  • fill with water, and cover the top.  
  • leave for 24 hours; when the cover is removed if it is full the clay is suitable for making or lining a clay pond. 

 

Suppliers of Puddling clay 

Puddling clay is still supplied by UK companies, cost about £60 plus delivery for a single ton, reducing to £5 per ton for multiple tons. 
If you can find a local building site where suitable clay for puddling is being excavated, the builder might be prepared to load you up for free. 
These are a few Puddling clay suppliers in the UK  
puddlingclay.co.uk  
wigginsbuildingsupplies.co.uk  
limedistributors.co.uk  
clwydtransport.co.uk
flowerpotman.com
 

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."