Cob: Re: cob, pise

Fri Jan 31 20:38:35 CST 2003

Jill inquired, <Let me see if I have this straight>

Jill made a serious inquiry about the different methods of construction and I will attempt to clear up a few things.  I realize that those of us who have been around for a while take things too lightly--and if I have I apologize.

Let's start with some basics.  All earthen compositions regardless of the terminology must accomplish one thing ---provide a strong building component.  If you look at the material ratios of clay, soil, sand or aggregate for cob, adobe or rammed earth, they are all essentially the same when used in their natural state. 

Straw  is an added component that that has to be used appropriately.  When used in cob or in more humid climates, the permeability of the structure in improved through the use of straw--it breathes better.  In less humid areas where rain fall is not a factor, you can do without the straw.  In many areas where there is not a sufficient amount of non-clay material, straw, grass or other organic materials will be used to minimize cracking and provide for a monolithic unit.

Pise and Rammeed Earth
NO-EQUIPMENT:  if this is the approach one is going to take, the forms can be simple.  Hand tamps do not provide the same amount of impact force as pneumatic equipment, therefore the lifts must be in the 2 or 3 inch range.  Any more than that, you will have weak or void areas when the forms are pulled.  The moisture content is critical and should be optimum based on the materials being used.  With hand tamps you will be fortunate if you achieve 90% compaction.   This would be identical to the material mix for CEB's (compressed earth blocks) made by machine.  Pozzolan based materials or cement may be added to the base material to add strength. This is a matter of choice.  If enough cement is used, you will not need a render or plaster.

Machinery and equipment for Pise and Rammed Earth
Tampers (powder-puff), usually about 6" in diameter is used to tamp the material.  It is similar to a pogo-stick with a plate of steel at the end and is run by compressed air.  Bobcats, tractors and conveyors are often used to deposit material into the forms.  Here the lifts can be 6" deep as the tamper is capable of achieving 100% compaction.  Over-compacting can blow-out a form.  Cement is optional and will achieve the same results as above.

Easton's Method for PISE
This is not rammed earth or Pise--it is concrete, be it a weak mix, that is applied.  It is no different than the methods used for guniting a swimming pool, lining a mine shaft or stabilizing a hillside.  It is the same equipment and process used for ferro-cement applications.  You can not achieve consolidation and compaction of soil and optimum moisture simply by blowing or guniting the material---it will fall apart.   Eaton's use of a high cement content is what makes his process work.  I works and is successful--but expensive.

All earthen construction has limits as to how high you can build.  The aspect ratio is the limiting factor.  This is another topic onto its own.

Re-bar or reinforcing steel will work only if can be encapsulated to utilize its properties.  It has very little beneficial use in cob, adobe or CEB construction.  When used in a rammed earth or a-la-Easton process,  you enrich the material around the re-bar with cement to create a beam or column.

Hope this has helped a wee bit.

SANCO Enterprises, LLC
Paul Salas, General Manager
P.O. Box 45741
Rio Rancho, NM  87174
(505)  238-1485
chansey at earthlink.net

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<DIV><FONT size=2>Jill inquired, <Let me see if I have this 
straight></FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2>Jill made a serious inquiry about the different methods of 
construction and I will attempt to clear up a few things.  </FONT><FONT 
size=2>I realize that those of us who have been around for a while take things 
too lightly--and if I have I apologize.</FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2>Let's start with some basics.  All earthen compositions 
regardless of the terminology must accomplish one thing ---provide a strong 
building component.  If you look at the material ratios of clay, soil, sand 
or aggregate for cob, adobe or rammed earth, they are all essentially the same 
when used in their natural state. </FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2>Straw  is an added component that that has to be 
used appropriately.  When used in cob or in more humid climates, the 
permeability of the structure in improved through the use of straw--it breathes 
better.  In less humid areas where rain fall is not a factor, you can do 
without the straw.  In many areas where there is not a sufficient amount of 
non-clay material, straw, grass or other organic materials will be used to 
minimize cracking and provide for a monolithic unit.</FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2>Pise and Rammeed Earth</FONT></DIV>
<DIV><FONT size=2>NO-EQUIPMENT:  if this is the approach one is going to 
take, the forms can be simple.  Hand tamps do not provide the same 
amount of impact force as pneumatic equipment, therefore the lifts must be in 
the 2 or 3 inch range.  Any more than that, you will have weak or void 
areas when the forms are pulled.  The moisture content is critical and 
should be optimum based on the materials being used.  With hand tamps you 
will be fortunate if you achieve 90% compaction.   This would be 
identical to the material mix for CEB's (compressed earth blocks) made by 
machine.  Pozzolan based materials or cement may be added to the base 
material to add strength. This is a matter of choice.  If enough 
cement is used, you will not need a render or plaster.</FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2>Machinery and equipment for Pise and Rammed Earth</FONT></DIV>
<DIV><FONT size=2>Tampers (powder-puff), usually about 6" in diameter is used to 
tamp the material.  It is similar to a pogo-stick with a plate of steel at 
the end and is run by compressed air.  Bobcats, tractors and conveyors are 
often used to deposit material into the forms.  Here the lifts can be 6" 
deep as the tamper is capable of achieving 100% compaction.  
Over-compacting can blow-out a form.  Cement is optional and will achieve 
the same results as above.</FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2>Easton's Method for PISE</FONT></DIV>
<DIV><FONT size=2>This is not rammed earth or Pise--it is concrete, be it a weak 
mix, that is applied.  It is no different than the methods used for 
guniting a swimming pool, lining a mine shaft or stabilizing a 
hillside.  It is the same equipment and process used for ferro-cement 
applications.  You can not achieve consolidation and compaction of soil and 
optimum moisture simply by blowing or guniting the material---it will fall 
apart.   Eaton's use of a high cement content is what makes 
his process work.  I works and is successful--but expensive.</FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2>All earthen construction has limits as to how high you can 
build.  The aspect ratio is the limiting factor.  This is 
another topic onto its own.</FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2>Re-bar or reinforcing steel will work only if can be 
encapsulated to utilize its properties.  It has very little beneficial use 
in cob, adobe or CEB construction.  When used in a rammed earth or 
a-la-Easton process,  you enrich the material around the re-bar with 
cement to create a beam or column.</FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2>Hope this has helped a wee bit.</FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV>SANCO Enterprises, LLC<BR>Paul Salas, General Manager<BR>P.O. Box 
45741<BR>Rio Rancho, NM  87174<BR>(505)  238-1485<BR><A 
href="mailto:chansey at earthlink.net">chansey at earthlink.net</A><BR></DIV>
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