Expanded clay: why this substrate is so good and what else you can do with it

18.11.2022

A clean thing: That's why you should use expanded clay

Improves the indoor climate as no mold spores form
Advantage for house dust allergy: no breeding ground for allergens
Heat and sound insulating properties
Improves the nutrient absorption of your plants
Prevents parasites and pests
Clean and easy repotting without much effort
Reusable: a clear price advantage

These are just a few of the benefits of expanded clay. Whether in gardening and landscaping, in construction, or directly in your household. The possible uses are diverse. We'll look at a few options below.

What is expanded clay and how is it made?

Expanded clay is, as the name suggests, expanded clay. To achieve this, low-lime clay is ground with organic components and then granulated, i.e. processed into small grains. These grains are burned together with a release agent, usually very finely ground limestone, at around 1200°C in a rotary kiln. This extremely high temperature has several effects:

On the one hand, the organic components inside the grain are burned and the resulting carbon dioxide ensures that the small grains become real balls. It puffs up the grains. Up to a volume that is 4 to 5 times larger than before firing.
On the other hand, the burning of the organic components ensures that small air pores remain. Depending on the size of the sphere, these can be thousands of tiny pores. This gives the expanded clay its partial heat and excellent sound-insulating properties.
In addition, the outer shell of each ball is sintered. So the surface melts and compacts. This makes the small balls almost impermeable to water and protects the air pores inside.

By constantly rotating the oven, the expanded clay retains its spherical or kidney shape. The release agent now ensures that the small balls don't stick together afterwards. The balls are then sorted according to different grain sizes and we have our expanded clay in different grain sizes.

The end product is light, odorless, structurally stable and chemically neutral. It cannot mold, rot or rot. It is also fire-resistant, frost-resistant, regulates moisture and has heat and sound-insulating properties. A product that is designed to be durable and even reusable depending on use.

Who actually came up with the brilliant idea of making expanded clay?

We find the origins of this in the USA in 1917, in Birmingham, Alabama. The inventor is S. J. Hayde and this name is still a common name for expanded clay in the USA today: Haydite. Only a year later, in 1918, there was the first patent for expanded clay that could be used economically and for construction purposes.

However, it was not until 1944 that the process was taken up in Europe. Here it was the Danes who further developed the process and introduced a brand of expanded clay that is still well-known today: Leca. This stands for lightweight expanded clay aggregates.

Now other countries followed suit and new brands came onto the market. Such as Sillit from Sweden, or Keramsit from the USSR. In 1955 the time had come in Germany too. The first factory opened its doors in Hennstedt, Schleswig-Holstein.

What possible uses are there for expanded clay?

There are different grain sizes for expanded clay, ranging from just 1mm to 40mm. And depending on whether the sound is still round or broken, there are different possible uses for it. Round clay is, as described above in the production, almost impermeable to water. So largely closed-pored. This clay is mainly used for insulation, drainage or hydroponics. However, broken expanded clay is partially open-pored because the air pores inside have been exposed. This means that it can absorb water and nutrients better. Similar to the well-known Seramis, which is completely open-pored, this can be used as an alternative substrate to the usual soil.

Use expanded clay as a substrate in hydroponics

Like every living thing, plants also need oxygen to survive. The expanded clay balls give the plant just as secure a hold as soil, but leave so many cavities due to their shape that the roots can spread unhindered. The clay granules allow a lot of oxygen and water to reach the plant roots. If the oxygen content is too low at some point, the roots will stop growing.

In contrast to soil cultures, a plant in hydroculture is constantly in water because the substrate itself does not store water. You should make sure that you use the right amount of water. If the water level is too low, the roots may not reach into the water and therefore cannot absorb nutrients. You also have to water more often due to evaporation. However, there shouldn't be too much water either. So-called water level indicators, also known as pegulators, can help here. In conjunction with appropriate pots for hydroponics, such as those from Leni, watering is pleasantly clear and easy. Please take a look at our Leni range: Leni range.

Since expanded clay itself does not contain any nutrients, these must be supplied directly via the water. There is liquid fertilizer that you can use. However, a fertilizer specifically developed for hydroponics is much more popular here: Lewatit HD50. These granules release their nutrients evenly over a longer period of time and ensure that you only need to fertilize every 3-4 months. However, the fertilizer is only suitable for ornamental plants. For vegetables and fruits, you should use a liquid, mineral fertilizer. We advise against using organic fertilizer in hydroponics as it cannot work due to the lack of soil life. It would just settle at the bottom and cause a bad smell.

The substrate should be rinsed properly at least once a year to remove salt residue and other deposits. Over time, mineral fertilizer, for example, leaves behind lime deposits that are often mistaken for mold. These are still not good and should be flushed out. If rinsing is not enough, you can also unpot the plant, wash out the expanded clay in a bathtub or similar and then repot the plant in the fresh substrate. We'll explain how to repot your plants correctly in one of our next posts.

We recommend adjusting the grain size depending on the plant when potting or repotting. For cuttings and young plants, 2-5mm is a good choice. If no or hardly any roots have developed yet, the plant will not find support in the expanded clay. The finer clay granules provide a remedy here. Later you can repot into a coarser grain.

The 4-8mm grain size is very suitable for small and medium-sized plants. Everything that is on your table or windowsill will feel comfortable there.

For the large planters it should then be the 8-16mm grain size. This would also be suitable for all types of drainage. But more on that below.

If you would like to try expanded clay as a substrate, take a look here: Cultivalley expanded clay. We offer grain sizes 2-5mm, 4-8mm and 8-16mm in quantities from 5L to 1500L.

Other uses for expanded clay

There are many other ways to take advantage of the benefits of expanded clay. As drainage, for example, expanded clay is useful in various areas. It supports soil percolation in general, or in gardening and landscaping with soil improvement, also known as melioration. Another example is in plant breeding as a drainage aid for soil crops. A layer of a few cm significantly improves water drainage and thus prevents waterlogging and root rot. A root fleece between the expanded clay and the soil ensures that the roots stay up in the soil.

Expanded clay can be used excellently as a soil loosener. Just 20-30% expanded clay in your plant or garden soil ensures that the roots get more air and can develop better. In addition, the risk of waterlogging and mold formation is reduced. Depending on how loose you want the substrate to be, you can simply use a little more or less, or a larger or smaller grain size.

It can also be used as ground cover or mulch. A few cm high layer of expanded clay on your soil prevents the rapid evaporation of irrigation water and also offers better protection against pests. Weeds also have less success with this.

Expanded clay is very light and is therefore very suitable as a plant substrate for green roofs. You should use a rather coarse grain size. More air for the plants, better drainage and less weight for the roof. We have one with 8-16mm on offer that can be used well for such projects: Cultivalley expanded clay 8-16mm 50L.

Expanded clay can also be used as salt-free grit on the paths in winter. In this case, a finer grain size is recommended. You can find 2-5mm clay from us that is suitable for this: Cultivalley expanded clay 2- 5mm 25L.

The clay granules have also excelled when used as insulating material. Due to the high thermal conductivity, the thermal insulation effect is unfortunately not as good as with other insulation materials. Therefore it is often combined with other substances. However, the ability to store a lot of heat is definitely an advantage, for example in houses that heat up quickly in summer. In addition, expanded clay has excellent sound-insulating properties and is even safer than other insulation materials due to its fire resistance. All of this makes expanded clay a valuable addition to bulk insulation.

Do you have your plants in expanded clay? Or are you using it for another purpose? Then write it down in the comments below. We would love to read about your experiences!

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