Expanded clay pellets are light, round granules of fired clay with a porous core and a closed, hard outer shell. They are made by firing clay at high temperature in a rotary kiln, where it puffs up like popcorn. In the Netherlands and Belgium the material often goes by the brand name Argex, elsewhere by names such as Leca. The Dutch term is kleikorrels.
Thanks to the trapped air, expanded clay is far lighter than sand or gravel, while still being crush-resistant, non-combustible, frost-resistant and rot-proof.
Where it is used
- Lightweight fill — on soft ground, filling with expanded clay adds far less weight, and therefore far less settlement, than sand
- Insulating fill — as levelling and insulating fill in floors, between joists and around services in a screed
- Lightweight concrete — as aggregate instead of gravel, for concrete of lower density
- Drainage — as a drainage layer under terraces and in roof gardens and planters
- Crawl space — a layer over the crawl space floor as ground insulation
Points to watch
- Crush-resistant, but not unlimited — loose fill is not a structural floor; it needs a spreader board, screed or bound layer over it
- Bound or loose? — loose granules let air, and therefore moisture, through; bound with cement they are stronger but insulate less well
- Judge the insulation value realistically — expanded clay insulates clearly better than sand or concrete, but far less well than a genuine insulation board of PIR, EPS or mineral wool. For a specific U-value target, a board is more efficient
- It floats — if the crawl space floods, loose granules can float up and shift
- Dust — wear a dust mask when pouring large quantities
Related terms
- Argex
- Lightweight concrete
- Ground insulation
- Crawl space
- Drainage
- Clay
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