[Cob] Cobhouse Design

[howard at earthandstraw.com]

You are welcome. 

BTW I have seen people say to put earthen plaster under lime plaster which I want to caution people against.  I don't think its wise to put a harder plaster over a softer one from my experience as it messes with the bonding.  

The lime bonds into the straw bales very strongly.  Plaster on cut ends of the straws, no mesh required nor control joints for cracking.  This is true even if you plaster up a foundation, across a wood band and onto the straw.  We always build a toe up or a drain bed for the bales.  Stack the bales flat and cut the folded side of the bale with a weedeater to so you can push the plaster into the straws.  At posts or wherever we feel we need it we do use cob, light clay straw or something in between to pack the holes.  We paper wood posts with Tyvek or felt and use strips of EML lapped across the potential gap onto the straw 1-2".  This seems to work but if you want to build with less money and more naturally I'd just plaster on across and see what happens.  Its fairly easy to fix if it does crack.  Or were you building a load bearing wall?

Now if you are intending to have a cob veneer inside to thicken up on the thermal mass, only 6 or 8 inches, you might want to tie some strings to the bale strings in each course so you could tie them to a deadman rod in the cob that could help tie the cob to the straw wall.  Then you will be plastering on cob.  I always thought it wise to leave a lot of straw sticking out and thumbholes in the cob as keys for the plaster to grip the wall with.  What experience have others had with this?

Have a good time,


Howard Switzer, Architect
668 Hurricane Creek Road
Linden, TN 37096
931-589-6513
www.earthandstraw.com
  ----- Original Message ----- 
  From: Marilyn Pratt 
  To: howard at earthandstraw.com 
  Sent: Thursday, April 09, 2009 1:06 PM
  Subject: Re: [Cob] Cobhouse Design


  Wow, THANK YOU for sharing this!!!  You just saved anyone who is reading this a few years of testing.
  -marilyn p.




------------------------------------------------------------------------------
  From: "howard at earthandstraw.com" <howard at earthandstraw.com>
  To: Barbara Roemer <roemiller4 at gmail.com>; coblist at deatech.com
  Sent: Thursday, April 9, 2009 8:31:06 AM
  Subject: Re: [Cob] Cobhouse Design

  We have taught and built many straw bale buildings over the years but I learned the most about plasters when I tore one down.  It was a small experimental building that we had tested many plaster recipes on at the Ecovillage Training Center, beginning with straight earthen plasters, mixed with various fibers, some mixed with sawdust, then some lime/clay and on to full lime plaster.  What I learned was that the lime and lime/clay plasters surface bonded the bales together but the all earthen plasters did not.  I could bang the earthen plasters off with a sledge hammer just ramming the wall knocking all the plaster off but when I got the lime/clay plasters I had to go to full swings with the hammer and do so along the course lines in order to break the bale out of the wall.  It became a lot of work on the lime and lime/clay portions of the building.  I recommend lime or lime/clay plaster for the first two coats on bales to protect them from insect or rodent infestations then what ever you want for a finish coat.


Howard Switzer, Architect
668 Hurricane Creek Road
Linden, TN 37096
931-589-6513
www.earthandstraw.com
  ----- Original Message ----- 
  From: Marilyn Pratt 
  To: howard at earthandstraw.com 
  Sent: Thursday, April 09, 2009 1:06 PM
  Subject: Re: [Cob] Cobhouse Design


  Wow, THANK YOU for sharing this!!!  You just saved anyone who is reading this a few years of testing.
  -marilyn p.




------------------------------------------------------------------------------
  From: "howard at earthandstraw.com" <howard at earthandstraw.com>
  To: Barbara Roemer <roemiller4 at gmail.com>; coblist at deatech.com
  Sent: Thursday, April 9, 2009 8:31:06 AM
  Subject: Re: [Cob] Cobhouse Design

  We have taught and built many straw bale buildings over the years but I learned the most about plasters when I tore one down.  It was a small experimental building that we had tested many plaster recipes on at the Ecovillage Training Center, beginning with straight earthen plasters, mixed with various fibers, some mixed with sawdust, then some lime/clay and on to full lime plaster.  What I learned was that the lime and lime/clay plasters surface bonded the bales together but the all earthen plasters did not.  I could bang the earthen plasters off with a sledge hammer just ramming the wall knocking all the plaster off but when I got the lime/clay plasters I had to go to full swings with the hammer and do so along the course lines in order to break the bale out of the wall.  It became a lot of work on the lime and lime/clay portions of the building.  I recommend lime or lime/clay plaster for the first two coats on bales to protect them from insect or rodent infestations then what ever you want for a finish coat.


  Howard Switzer, Architect
  668 Hurricane Creek Road
  Linden, TN 37096
  931-589-6513
  www.earthandstraw.com
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