On 25 Jul 06, at 12:27, Adam Fikso wrote: > ...Has anyone checked the degree of coarseness of Perlite used > in building construction for insulation or manufacture of ceiling > insulating tiles? I can imagine that it might be much cheaper even > though it might not be packaged in less than cubic yard or carload > lots. A reminder that such perlite *may* contain fluorides, which can damage your plants. Perlite sold as "horticultural" is selected to be free of fluorides. There's no certainty where other kinds are concerned. N.B. "may" "can" "no certainty" -- Rodger Whitlock Victoria, British Columbia, Canada Maritime Zone 8, a cool Mediterranean climate on beautiful Vancouver Island