Note: The thermal insulation value is a function of bulk density and particle size; generally the lighter the mix the greater the thermal insulation will be. When the same volume of different grades of exfoliated vermiculite are incorporated into a standard mix, the final density (and therefore, the thermal insulation) will be influenced by the fact that the finer grade of the vermiculite used the denser the product will be. Conversely, a mix based on coarse and mid-sized exfoliated vermiculite will generally have the same thermal insulation value at ambient temperatures, but, at elevated temperatures the finer particle size aggregate concrete will be more insulating due to a lower thermal diffusion.
For vermicrete mixes I use a 50/50 (by volume) mix mixture of fine vermiculite and medium perlite for the above reason. It also makes up a more workable mix to apply, particularly useful in the leaner mix proportions.
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