Puddled clay is the traditional material for lining canals and other artificial waterways, as well as for repairing leaks in earth dams, and sealing joints between concrete and earth banks.
To puddle simply means to pound clay and water together in a dense mass which resists water penetration. Puddling breaks down the structure of the clay, closing fissures and forcing out air bubbles. The clay becomes very plastic, just as happens when it is made into pottery.
Puddling of the clay which lines the canal system in Britain was done by driving flocks of sheep into sections of the constructed and lined canal, so their trampling puddled the clay. Dew ponds and other small water bodies were puddled by sheep or human feet. Mechanical puddling can be done using a dumper or JCB.
Advantages
- A puddled clay lining may be very cheap if suitable clay is available nearby. Contact local developers, haulage contractors, plant hire or skip hire operators, as suitable clay may be available as a waste material from local development schemes.
- No special equipment or tools are necessary, other than those needed to transport the clay. Provided the area is not too large, puddling is a fun way of involving a group of people. Children especially enjoy it.
- A successfully puddled clay bottom is virtually immune to leaks, decay and vandalism, provided it is made sufficiently thick, and is always covered with water.
- A puddled clay lining can be cleaned by hand of silt without damaging the lining. However, great care must be taken if using machinery.
- Leaks in puddled clay linings can be traced and repaired relatively easily, provided the water level can be lowered temporarily.
Disadvantages
- Purchase and high transport costs may make clay expensive. It is not always possible to locate a reliable supply at the time that you want it.
- If done by hand, the process of spreading the clay is heavy and laborious work. Puddling must be meticulous to be successful, and the lining must be prevented from drying out while it is being constructed.
- Puddled clay is liable to crack if the water level falls and exposes the lining for any extensive period. When the level rises again, the clay is no longer watertight.
This often causes problems on ponds or canals which are restored after a period of dereliction, and may be the true cause of continued leakage from ponds where repairs are undertaken on supposedly faulty dams. - Cattle or horses may damage the lining, although sheep can improve it by sealing any small cracks which may form. Normally clay-lined ponds should be fenced against stock. Where access is required for watering stock, the clay should be surfaced with a thick layer of gravel or chalk with flints.
Preliminary requirements
Calculate the cubic contents of the lining required. Pond linings should be 200-300mm (8-12”) thick, and thicker if they are subject to erosive wave action or trampling by cattle. Canal linings must be 300mm-1m (1-3’) thick. When ordering, allow about a third extra for ‘bulking’ as the clay is supplied unconsolidated and much of its volume is air.
The clay must be of suitable quality, as shown by the following test. When the clay is moistened and kneaded you should be able to roll it into a ‘sausage’ which can be bent into a tight circle with no cracks. The clay should be totally free of stones and any organic material, and should feel silky and smooth. When mixed with water in a container any impurities such as sand will fall to the bottom. Clay which contains shiny particles of mica is unsuitable.
The prepared excavation should be reasonably dry and firm, and free of large stones, stumps and roots. Make all slopes very gradual, as wet clay banks are very slippery and dangerous, being easy to slide into but difficult to get out from.
If puddling without machinery, the only items of equipment needed are wellington boots, buckets for water and shovels. Some dew pond makers used a special tamper.
Procedural points
- The action of puddling clay requires no skill, but it must be done slowly and methodically. Puddle the clay in thin layers and build it up slowly, otherwise it will not be watertight, and different sections may not knit together.
- Each puddler should work on an area of about a square metre, and puddlers should be stationed so that no unpuddled areas are left between. The group should concentrate on one portion of the lining at a time, rather than being spread out across the whole area.
- Divide the work between shovelling and carrying the clay, and puddling. Swap the two groups over from time to time.
- Shovel the clay as supplied, and as each shovelful is spread on the square, add just enough water to make the clay plastic. Excess water will be trapped in the clay, weakening it. Keep treading up and down all the time, working the water and air bubbles out of the clay, and knitting your area together with those of adjacent workers. Add another shovelful only after all the voids have been worked out of the clay being puddled.
- Avoid adding too much clay at one time. This is tempting, especially when using a dumper, but it results in a compacted top surface while the clay below remains fissured and liable to leak.
- Complete the first layer to a depth of about 75mm (3”), before starting on the second layer. This ensures that no hard-to-puddle joints occur between different sections.
- Bring the puddling well up the bank, making the sides the same depth as the bottom. Be sure to cover any possibly faulty masonry or joints between different materials, where leaks are likely to occur.
- The surface must be kept wet at all times to prevent cracks forming, which, unless carefully sealed by repuddling, may cause leaks. If the task must be discontinued for even a day or two the clay should be hosed periodically or flooded in the interim. A small work area can be covered with polythene to prevent moisture evaporating.
- Don’t worry about small amounts of standing water, or about it raining while puddling. Avoid puddling clay in frosty weather since it will crack and heave due to the expansion of water when it turns to ice. If the job is partly done and frost is likely, it is best to flood the site deep enough to prevent it freezing the lining.
