I have never read a strict rule of how much to put in your wood shavings. I just calculated that I use at least 10% DE to shavings. I never looked at it as an exact science. I figure if it smells nice and is dry it must be ok. If it stanks and is wet, I need fresh shavings and more DE.
If I am trying to control something like insects or whatever, I obviously must use enough to actually coat whatever pest it is i want to get rid of. If there is so little that the pests can walk all around and not come into contact with it, it should be common sense that it won't work. You have to make sure you put enough so the pests can't avoid it and have to come in contact with it. Also if you are trying to freshen your animal bedding, you should obviously have enough in there to actually do something or its a waste of time to even bother. That's how i approach it.
So when I sprinkle it over the bedding I want at least a thin, solid coating on the top of the shavings, nothing less than that. Then I stir it in and hope it's enough to actually do something.
