Cob: Use of Forms?

[Darel Henman]

Joe,
  Thank you so much for the information.  
  About a use for the chalk, it can be fired with coal at about 950 to
1,000 degrees celcius (C) for a day or two (or for as long as the coal
burns?) and produce raw lime, some call it quick lime? (from the calcium
carbonate in the chalk).  I wouldn't be surprised if this was what was
used for the lime washes used on the earthen buildings.   I was alway
curious about the sources for the building lime in other countries.  
Some places used (still do) oyster (or other shellfish) shells to fire
to produce raw lime.  I've heard this can be done with freshwater shells
as well.

Darel

Joe Skeesick wrote:
> Actually in the UK the terms used are cob and clay lump. (which according to
> my understanding of "rammed earth" is more in keeping with what is being
> described here than the later term). Clay lump is simply a more moist
> mixture of cob that is shuttered, then turned out but the contents of the
> mix are basically the same. The end result of both building types is
> basically the same (with obviously more uniformity being the result of the
> clay lump type).
> 
> My area of the country (East Anglia) has a significant number of clay lump
> buildings where as the South-West took more to cob. The reality being that
> the most significant difference between clay lump and cob is the term
> itself. Some cob in the west (UK) was also shuttered and rammed as well.
> Both are monolithic load bearing earth structures and (I think) fall easily
> into the modern definition of "cob". Rammed earth is a term used much more
> often with using full forms, interregnal reinforcements (rebar) and
> typically a cement stabilized earth mix (and of course copious use of
> powered equipment).
> 
> On the topic of chalk, to my knowledge no large amount of chalk was
> implemented into the mix directly. Typically you simply dug down to the
> chalk layer and built atop it as bedrock. Current building practices here
> require a set depth foundations must run to however and you are often forced
> to dig a significant depth into the chalk itself (at great effort for no
> good return). As for what chalk is and the definition. Next time your in a
> classroom pick up that little white stick resting under the blackboard and
> have a look. Just like that only in big slab formations 1-3 feet down. I
> have a big block of it out by the forge that I chip of a piece to mark with
> as needed. But to build with it? It has similar characteristics as sand
> stone.... great with compression when left in the ground but very poor at
> dealing with shear forces. I am however far from the end all on questions
> like this. It might well be used in 100 ways I'm unfamiliar with.
> 
> Joe
>