Quote:
Originally Posted by Willow87
How long does it usually take to break down? I read from a few horticulturist that it doesn't break down like perlite and that it can be used for long term. That's the first negative thing I've seen about expanded shale. Alot of people have recommended it.
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Perlite is both a naturally-occurring and human-made foam from silicate minerals. It breaks down physically (i.e., crumbles) over time into glass silicate particles.
Expanded shale is manufactured from coal mine tailings (shale) by a similar process. It is slow to break down physically, but breaks down chemically (most notably from fertilizers) into clay silts.
Straight from the factory, expanded shale is sold for about US $6 per 4 cu.ft. sack, $30 per cu.yd., or $450 per container-load (not including freight). These are the same as manufacturers' prices for Perlite. So something is clearly wrong with the high prices and high-hype levels surrounding expanded shale.