Vermiculite is a natural mineral related to the mica group. It has layers of silicate plates with water molecules bonded between them. On rapid heating the plates “exfoliate” into a long wormlike structure, from which the name vermiculite is derived. The expanded structure is quite weak and easily squashed. Pressed insulation bricks have been made from vermiculite for generations, some good, some bad, but pressing vermiculite into bricks compacts the material and a lot of the insulation value is lost.
Conventional monolithic insulation based on vermiculite and mixed in a pan mixer, also squashes the particles to higher density.
In Rapolite technology the mixing is done in an ordinary concrete mixer and poured in a runny, watery consistency into the mould. It looks like it could never set and it looks like it will segregate disastrously. However, 20 minutes later the mould can be stripped to reveal a superb microstructure. This super-gentle mixing does not compact the vermiculite at all.
The wet density is 1,0Kg/ litre and the dry density is 0,33Kg/ litre.
In Rapolite technology the matrix between the expanded vermiculite particles is filled with a finer silicate, to further enhance the insulation value. The thermal conductivity is approximately 0,2W/mK. The microstructure is very much finer than that of vermiculite bricks or board.
Castings should be left to air dry naturally, as their permeability is low.