[Lowfer] Not a RotoHammer, but a good pilot hole starter

[JD]

Thanks for the comments thus far on sources of bentonite.  What I have found 
thus far is that there are more than one type of the stuff, and not all 
types might be all that useful.

Sodium bentonite is the type that folks around here seem to recognize. 
Although we don't have many water well drillers in this area, or even oil 
wells all that close, some of my neighbors turned out to be aware of its use 
in reinforcing earthen dams.  It's also what the mega-landfill operators in 
the region use for their impermeable clay barriers and geosynthetic liners. 
But that, I suspect, could be a problem.  Once it has had a chance to 
harden, it is no longer so eager to reabsorb water.  I wonder what that 
would do to my ground resistance?

Calcium bentonite is what they use for absorbing oil, the application JB 
mentioned.  That seems to be one of its specialties, and if the calcium 
retains its affinity for water after consolidation, then it might be better 
for my use.  Anyone got any thoughts on that?

And, anyone know which type the bentonite in cat litter actually is?

Thanks.

John