[GSBN] Harry Francis' "Lime + clay bond "message from SB-r-Us archive

Jacob Deva Racusin buildnatural at googlemail.com
Tue Apr 22 20:37:10 CDT 2014

Thanks Rob, I appreciate your digging and reporting.  I think I got most 
of that right...thanks again Harry for your insights!


On 4/22/14, 1:35 PM, Rob Tom wrote:
> On Tue, 22 Apr 2014 GSBN Digest, Vol 36, Issue 17
> Jacob Deva Racusin <buildnatural at googlemail.com> wrote:
>> Subject: Re: [GSBN] lime over hessien
>> Does anyone else have recollection of that[ lime /clay bonding ] thread?
> I just looked in on the SB-r-Us site for the first time in a long time 
> and to my dismay, it appears that Yahoo has been monkeying around with 
> the format so that the list archives are no longer arranged neatly by 
> month/year so accessing it is a bit different than what I had been 
> used to. ( FUBAR was my initial reaction)
> However, by entering "lime over clay plaster Harry Francis" into the 
> search facility the following message was returned:
> ==================== copied material ========================
> CALXA at aol.com wrote:
> Hi Mark,
> In order for the lime to react with silica, the lime must be of 
> sufficient amount to raise the pH of the silica to above 11, forming a 
> natural pozzolonic cement..... In the case of the lime applied to the 
> surface of a clay wall, this can happen at the interface, but beyond 
> the interface, the remaining unused lime only raises the pH of the 
> clay somewhat. At this point the clay becomes silty, and no longer has 
> the strength of clay...setting up a situation where there is no longer 
> any bonding strength.
> In treating soils with lime to make soil cement, we expect the clay 
> content of the soil (minus 200 mesh) should be in excess of 10%. Below 
> that level, the silica content is insufficient to make sufficient 
> calcium cement interspersed to give the result needed strength. If 
> less than 10%, it often makes sense to use portland cement to create 
> structural materials.
> As to testing lime clay blocks for water durability......It is a way 
> to show the weathering potential...BUT I don't think it would show the 
> potential of lime plaster to separate from a clay block.
> However if the blocks (or wall structures) are made of clay lime 
> mixture (sufficient lime to fully stabilize the clay), creating 
> natural cement (pozzolonic reaction), then I would think that lime 
> plaster would now adhere very nicely.
> By making a lime/Clay block that does not deteriorate in soaking, then 
> let dry, and then applying lime plaster, one should be able to 
> evaluate if a bond has resulted. Some natural occuring clays may also 
> show this result....and asI mentioned earlier, every Clay is 
> different...so to be on the safe side, one should test combinations.
> Even a small amount of lime , say 2-3 % by weight of a soil, will 
> agglomerate the clay soil into silt like structure, but not give it 
> cementing  strength. We call this soil modification... and is often 
> used in heavy clay soils to improve agricultural use of the soil. 
> Heavy clays form an almost impermable layer making the growth of crops 
> almost impossible, as the soil no longer breathes.
> Hope this all makes sense,
> Harry
>  > In a message dated 2/16/2009 1:01:24 P.M. Eastern Standard Time,
>  > mark at lowenergydesign.com <mailto:mark%40lowenergydesign.com> writes:
>  >
>  > Thanks for this Harry. But I'm still trying to make sense of this
>  > chemically. In your previous post (quoted by Bill) you said:
>  >
>  > " You are correct in noting the different materials and no chemical 
> bond
>  > between clay and lime plaster. As the two meet, the clay is 
> modified to
>  > a silt like soil, losing its strength, and destroying any bond between
>  > the lime and the clay. Thus it laminates and falls off."
>  >
>  > Whereas in the latest post (immediately below) you talk about the
>  > lime-silica reaction.
>  >
>  > At first sight these statements appear mutually contradictory - could
>  > you resolve this for me? Is it something to do with the lime bonding
>  > preferentially to the silica in the lime plaster itself? (in the sand)
>  > Or is it something to do with the aluminates and aluminosilicates 
> in clay?
>  >
>  > Also, can you recommend a decent book dealing with the chemistry of
>  > clay? - it might be easier to understand this stuff by going to first
>  > principles.
>  >
>  > Thanks
>  > Mark (a different one)
> ==================  End of copied material ==================
> (Yahoo tells me that there are 43 more messages in the above thread 
> but I didn't check to see what was in the balance of the thread)

Jacob Deva Racusin
New Frameworks Natural Design/Build

Author, The Natural Building Companion
Chelsea Green Press, 2012

(802) 782-7783
jacob at newframeworks.com

More information about the Gsbn mailing list