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

Rob Tom ArchiLogic at yahoo.ca
Tue Apr 22 12:35:39 CDT 2014

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  

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,


  > 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  
  > 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)

=== * ===
Rob Tom  .  .  .  T60BU
Kanata, Ontario, Canada

< A r c h i L o g i c  at  Y a h o o  dot  C a >
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