[TowerTalk] Bentonite

[K8RI on Tower talk]

> Somebody mentioned Bentonite as a good filler material to improve
> grounding a few days ago. I asked around about this a bit and one of the
> tidbits that I got was the following:
>
> Commercial Bentonite comes in two general varieties (at least for
> construction purposes), High Solids and Low Solids. The High Solids form

Although Bentonite is basically clay, chemically there are two types, 
swelling (Sodium Bentonite) and non swelling (Calcium Bentonite).

As I understand High and low solids pretty much depend on the mix with 
water.
In one form it's used in oil and gas well drilling to seal the pipes into 
the strata through which they are drilled.

The ability of clay to hold or absorb a tremendous amount of water which can 
cause it to swell and contract is one of the reasons back filling around a 
basement with clay is not a good idea..

In this area there is a lot of clay.  It's not normally a problem, but we've 
gone through several rapic cycles between very went to very dry.  This is 
causing many basement walls to crack, including mine.  Ours had only pushed 
in about an inch while some in the area have moved far more.


> was reputedly  good for grounding while the Low Solids form was not. The
> story is that the Low Solids form, while absorbing water as any good
> Bentonite should, would still not be very conductive. However, the High
> Solids form was indeed very conductive when water was absorbed.
>
> The other bit was that it is Thixotropic, meaning that even after
> hardening, it will liquify with a good shaking. So it may be a bad
> choice to have around a tower base, especially in an earthquake zone.
>
> If anyone has any more information on this stuff, I'd be interested to
> learn more.

Think clay and Google is your friend as is Wikipedia which has a pretty good 
description.
http://en.wikipedia.org/wiki/Bentonite

Roger Halstead (K8RI and ARRL 40 year Life Member)
N833R - World's oldest Debonair CD-2
www.rogerhalstead.com

>
> Ben
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