A Clean Choice: Why You Should Use Expanded Clay
- Improves indoor climate, as no mold spores form
- Advantage for dust allergy sufferers: no breeding ground for allergens
- Thermal and sound insulation properties
- Enhances nutrient uptake of your plants
- Prevents parasites and pests
- Clean and easy repotting without much effort
- Reusable: a clear cost advantage
These are just a few of the benefits of expanded clay. Whether in landscaping, construction, or your own home, the applications are diverse. We’ll explore a few of them further below.
What Is Expanded Clay and How Is It Made?
Expanded clay is, as the name suggests, puffed-up clay. To achieve this, low-calcium clay is milled with organic materials and then granulated into small pellets. These pellets are mixed with a separating agent, usually finely ground limestone, and fired at around 1200°C in a rotary kiln. This extremely high temperature produces several effects:
- Firstly, the organic materials inside the pellets burn, and the resulting carbon dioxide causes the small pellets to expand into actual spheres, up to 4–5 times their original volume.
- Secondly, the burning of the organic components leaves tiny air pores, depending on pellet size there can be thousands. This gives expanded clay its thermal and excellent sound insulation properties.
- Additionally, the outer shell of each pellet is sintered. The surface melts and densifies, making the small spheres nearly waterproof and protecting the air pores inside.
Thanks to the constant rotation of the kiln, expanded clay retains its spherical or kidney shape. The separating agent ensures the pellets don’t stick together. After firing, they are sorted by size, giving us expanded clay in various granulations.
The end product is lightweight, odorless, structurally stable, and chemically neutral. It cannot mold, rot, or decay. It is fireproof, frost-resistant, regulates moisture, and has thermal and sound insulation properties. A product designed to be durable and even reusable depending on use.
Who Came Up With the Brilliant Idea to Make Expanded Clay?
The origins trace back to 1917 in Birmingham, Alabama, USA. The inventor was S. J. Hayde, whose name is still commonly used for expanded clay in the USA: Haydite. Just one year later, in 1918, the first patent was issued for commercially and technically usable expanded clay.
It took until 1944 for the method to be adopted in Europe. The Danes further developed the process and introduced a now well-known brand for expanded clay: Leca, standing for lightweight expanded clay aggregates.
Other countries followed, introducing new brands like Sillit from Sweden or Keramsit from the USSR. In 1955, the first plant in Germany opened in Hennstedt, Schleswig-Holstein.
What Are the Uses of Expanded Clay?
Expanded clay comes in various sizes from 1mm up to 40mm. Depending on whether the clay is round or crushed, its uses differ. Round clay is almost waterproof and mainly used for insulation, drainage, or hydroponics. Crushed expanded clay is partially porous, allowing better absorption of water and nutrients, similar to Seramis, and can be used as an alternative substrate to regular soil.
Using Expanded Clay as a Hydroponic Substrate
Like all living beings, plants need oxygen to survive. Expanded clay pellets provide plants with secure support like soil but create hollow spaces that allow roots to spread freely. The granules provide both oxygen and water to the roots. If oxygen levels drop too low, roots will stop growing.
Unlike soil, plants in hydroponics are constantly surrounded by water, as the substrate itself does not retain it. Careful monitoring of water levels is crucial. Too little water means roots might not reach the nutrients; too much water is also problematic. Water level indicators, called Pegulators, help maintain balance. Combined with suitable hydroponic pots, such as from Leni, watering is clear and easy. Check out our Leni selection: Leni Collection.
Since expanded clay contains no nutrients, they must be supplied via the water. Liquid fertilizer can be used, but a hydroponics-specific fertilizer like Lewatit HD50 is more popular. It releases nutrients over a longer period, requiring fertilization only every 3–4 months. Suitable only for ornamental plants; vegetables and fruits need a mineral liquid fertilizer. Organic fertilizers are not recommended in hydroponics as they cannot function without soil life.
Flush the substrate at least once a year to remove salt deposits and residues. Mineral fertilizers can leave calcium deposits often mistaken for mold, which should be rinsed out. If flushing isn’t enough, repot the plant, wash the expanded clay, and return the plant to fresh substrate. Adjust granule size based on plant stage: 2–5mm for seedlings, 4–8mm for small to medium plants, 8–16mm for large plants. Check out Cultivalley Expanded Clay for sizes 2–5mm, 4–8mm, and 8–16mm in 5L–1500L packs.
Other Uses of Expanded Clay
Expanded clay is useful as drainage in gardening, landscaping, and soil improvement (melioration). A layer of a few centimeters improves water flow and prevents root rot. A root fleece can keep roots in the soil layer.
It can also act as a soil loosener: 20–30% in potting soil improves root aeration and development, reducing the risk of waterlogging and mold. It can serve as mulch, reducing evaporation and protecting against pests and weeds.
Expanded clay is very light, ideal for green roofs. Use coarser granules (8–16mm) for better aeration, drainage, and reduced weight: Cultivalley Expanded Clay 8–16mm 50L.
Useful as salt-free winter grit or for loose-fill insulation. Stores heat, dampens sound, and is fireproof. For finer grit, use 2–5mm expanded clay.
While its thermal insulation is lower than other materials, its heat storage and soundproofing make it valuable for summer heat mitigation and acoustic insulation.
Have you used expanded clay for your plants or in other ways? Share your experiences in the comments – we’d love to hear from you!