[Cob] lime in with the clay

[howard at earthandstraw.com]

I guess what we are talking about with regards to lime is a matter of relativity.  Bang your head on the limestone and it will feel hard.  Since limestone is a formation of former living creatures it is bound to have some, and possibly considerable, variations.  I'm no expert, I only have my own experience and it does not involve Kansas limestone which sounds like it is not suitable for building with.   We get most of ours either from Ohio, famous for its limestone, or Alabama.  However, limestone is relatively soft compared to granite and certainly even Ohio limestone on buildings have had a hard time in the chemical soup we call our modern atmosphere as pollutants have reacted chemically with limestone in cities.  Well for that matter granite and marble are having a hard time weathering the storm as well.  I'm not familiar with the building you refer to but that is one common problem for limestone clad buildings. If the building you refer to is rotting from the inside out I wonder if it has been painted, which on brick or terra cotta often cause them to do the same as they are then not allowed to breathe.  It makes me wonder of the white wash doesn't keep the surface breathable and without it perhaps it forms an un-breathable crust on it acting much like the paint I refer to.  Perhaps someone knows or it is an area for further research.

However, lime generally does make a good stucco for buildings because it has benefits beyond its relative hardness, most of which I've already mentioned, as its long and excellent record in the human experience with it for many thousands of years attests.  I recently saw photos of the ancient process or baking limestone into quicklime still being used in Ethiopia today.  We also had a client once call me up to say, after the second coat of lime had dried on her walls, that she had taken a stick and by rubbing it hard against the plaster in one spot she was able to dig almost through the plaster. I asked her not to do that to her plaster. It takes 2-3 years for it to get to its full hardness but then its isn't so brittle it needs steel reinforcement like PC stucco either.  As far as longevity I can only say from my experience so far it is working beautifully,12 years and counting, with no signs of wear from weather on most of our buildings, some with tall exposed walls.  We did have one that a client had built which had some bad details that allowed a stream of water off of the roof stream onto a wall and there is some wear there just as a stream of water would wear granite away.  Maintenance for the lime stucco however may be the secret as a painting of more lime or lime/clay in a paint form (white wash) gives it another layer which bonds and adds up over the years.  Since buildings continue to be protected with lime all around the world after several thousand years I wouldn't worry about it too much.  I would not go so far as to call lime stucco a folly, as you say we have to be careful about generalizations, but some variations do apply.

If you are looking for maintenance-free construction I assure there is no such thing.  The efforts to create such has resulted in toxic pollution and only a deferred maintenance that usually results in a much more difficult replacement or repair when the time does come.


Howard Switzer, Architect
668 Hurricane Creek Road
Linden, TN 37096
931-589-6513
www.earthandstraw.com
  ----- Original Message ----- 
  From: michael hollihn 
  To: coblist at deatech.com 
  Sent: Thursday, April 09, 2009 7:12 PM
  Subject: [Cob] lime in with the clay


  howard, thanks for your insights on lime, i live in bc and am pulling
  what's left of my hair out trying to find out if north america has any
  quality lime to build with, i will insert a bit of commentary that
  i've recieved from a greenbuilding list:

  > Limestone out of our local NE Kansas quarries do definitely not get
  > stronger over the ages.  This stone can be very soft, easily flaking
  > away or
  > literally melting in the rain.

  Sacie's experience with limestone is a fine example of the folly in
  bandying-about generalisations as fact because generalisations (including
  this one) are usually wrong.

  ----

  There are (relatively) old limestone buildings here in Ontario built in
  the 19th C that are self-destructing because the stone is literally
  rotting from the inside out (ie high iron content).

  And as Sacie mentions, there are very soft limestones, some that are soft
  enough to cut with a handsaw while still "fresh" from quarrying  (ie
  before the process of carbonation has gone on for very long to harden the
  outer portions exposed to the atmosphere.)
  "

  no one has been able to anwer me yet on these above statements about
  ontario and kansas lime, whether it was the fault of the builder or
  the lime, and whether or not there are quality sources of lime in
  north america

  -- 
  michael hollihn,
  british columbia,
  www.michaelhollihn.wordpress.com (bioregional timber frames)
  www.kettleriverfood.ning.com (building food security in the kettle
  River watershed)
  'Be the change that you want to see' ghandi

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