Very interesting bwd.
I still don't see any correlation between using sand, be it sterilised or not, on top of your soil and the claim to have never had any critters in your grow area, other than the odd wasp.
If you have never had any such critters why did you decide to use sterilised...
I don't see how sand on your soil would ever help control Thrips, Caterpillars, Aphids, Spider mites or most other critters except for Scarab fly larvae.
Try reading the thread "curing by the numbers" that Hick re-posted, originally written by Simon
http://www.marijuanapassion.com/forum/showthread.php?t=54451