Cob Lime dust

[Mike Carter]

>At 09:36 AM 7/21/98 -0500, you (Jeanne Leimkuhler) wrote:
>>Does anyone have information or experience with adding Limestone dust to
>>concrete, mortar or cob? It is a bit like gravel and can be had for
pennies
>>here in southern Indiana. We are thinking that it could add strength to
the
>>concrete and some water resistance.
>>Adding it to cob seems more problematic. It might continue to expand and
>>contract if it absorbs water. Is it more like the clay or the sand?
>
We have used "dry screenings" from crushed local limestone for all of our
Cob.  Engineering tests showed that this made a much stronger mix than sand
alone.  I am convinced that the "dry screenings" as they are called here
have properties of both sand AND clay depending on particle size - when wet
and tamped by itself, it forms a hard surface that even fire ants won't go
into but doesn't crack.  We also use this in small amounts in all of our
custom "Cob mortar" mixes.

Mike Carter