Cob: Re: earth floors

[Darel Henman]

Matthew,

Re:
> Thanks for all the feedback and ensuing discussion, but has anybody actually TRIED adding PVA
> adhesive to mud renders etc.

This is for lime-sandy mud mixture renders, with with or without added
small hemp or straw fibres.

Hundreds of years ago the chinese made a "sweet rice", aka mochi rice
paste.  This was used in Japan as well and added to a lime earth mud to
basically help it hold water longer to make application easier.  It was
not used on the outside surfaces as when it dried I believe the alkalai
pretty much ruined the glue and it was not water resistent.

This kind of glue was extremely expensive and could only be used by the
temples or very wealthy folks.  Since it was made from a foodstuff,
rice.

Later in Japan they learned how to make a glue for lime-mud out of some
kinds of seaweed.  And it has been used extensively for hundreds of
years and can still be bought.  However, this is also only used for
interior used. 

Oil, has been added for exterior applications to give water resistence.

Here is some data by a lime-mud supplier in Japan it is in Japanese but
the numbers are, well numbers. The Japanese Institute for Standards
Standard for testing this was followed.

To help you navigate through the Japanese/Chinese charaters:  
There are six test samples,  three each of.
	1.) Shirokabe lime-mud mix (without oil)
	2.) The old traditional lime-mud mix (without oil) 
	3.) Shirokabe lime-mud mix with oil   ( 180 cc of oil / 20 Kg of
lime-mud )

This is a water absorption test.

columns
 Name  |  No.#  | pre-test weigh   |  1 hour 2cm submersion     | 5
hour     |   24 hour
       |        |  in grams        |    weight(g) |  H20% added |
weight|H20%| weht |HwO%
------------------------------------------------------------------------------------------
Shirokabe 1
          2
	  3
   average........
------------------------------------------
Traditional
	1.
	2.
	3.
   average ......
--------------------------------------
Shirobake 1
 with oil 2
	  3
   average
----------------------------------------------------------------------------------------


Note:  The first table in section three is after 4 weeks of curring.
       The second table is after 8 weeks of curring.

The Japanese characters may show up as garbage, if you can't read the
tables let me know.

Here is the data:  http://www.shirokabe.co.jp/kyusui.htm

Have fun.

I have heard that in Southwest North America that the natives used a cow
dung as an additive.  They'd add it to the mixture and let it age a
while.  Does anybody have any data for the effect of adding cow dung to
adobe mud?

Darel