[GSBN] Straw Preservation in Clay _ Research Documents

Thu Oct 24 22:41:36 UTC 2013

Dear Anthony

Afraid this comes as a rather delayed response, in regards your question
about the long term preservation of straw in clay.

Firstly I think is worth said that Bruce King's book "Design of Straw Bale
Buildings - The State of the Art" explains the science of it all rather
perfectly. As for research documents I cannot help but I nonetheless thought
a few tales were worth sharing 

Firstly I know an artist, Peter Eastman who used to work in the antiquities
department of the British Museum doing restoration work. He told me about
how unbaked clay can preserve straw perfectly for thousands of years. He
says that when restoring many old Egyptian sculptures, the easiest were the
ones made of unbaked clay, which many of them were. He said that when
working with them they would simply break down any shards of clay rewetting
it to remould broken limbs and such back together again. He said that
something that had always amazed him when busy with such works, was that he
would find bits of sparkling yellow straw in the clay and that despite its
1000's of years of age, nonetheless looked as fresh as if it had just been
harvested. 

The second was when I was travelling in a rather more humid Japan. In Kyoto,
I chanced across a demolition in progress of an old traditional Japanese
"wattle and daub" house. The old construction, which could have been
anything from 100 - 500+ years old consisted of a timber frame with infill
panels of timber and bamboo lattice work with a cob infilling, which had a
natural plaster on the one side and originally a timber cladding on the
exterior. Upon examination I noticed how the straw (rice straw no doubt) in
the cob used in the construction still looked and performed as new. The
contractors were dampening the place down with water while they bashed the
construction to the ground (sadly there are no heritage conservation laws in
Japan that protect old buildings) so I took handfuls of the damp cob and
worked it as if it were just newly made. I have attached some photos of  the
straw clay bamboo construction and another revealing the construction -
which hopefully  the server will allow..? If not then I will need to upload
it onto media fire and send out a link.

It was also interesting to note how vital moisture levels and air exchange
is to the survival of straw rather than age per se. After taking the
demolition photos, wanting to take a specimen with me, I snatched a sample
of the old somewhat sodden sample of the clay and final plaster layer.
Looking around I grabbed a handy piece of plastic and wrapping it up safely,
stuffed it in my pack and then forgot about it. That is until finally a
couple of weeks later when back home I unfurled the by now mouldy packet. To
my dismay all the straw had moulded away to nothing. The samples were wet
and because the wrapping did not breath, of course rot set in, ironic I
thought after surviving perfectly for hundreds of years beforehand.

I have also observed in demolitions of old works how timber that is buried
in clay, will be well preserved  especially in comparison with timber that
has been laid in concrete, which will normally be rotted away.

Best regards

Andy Horn

Eco Design - Architects & Consultants

A. R. Horn BAS, B. Arch, Pr Arch, MIA 

1st floor 79 Roeland Street, Cape Town, South Africa

+27 21 462 1614, www.ecodesignarchitects.co.za

From: GSBN-bounces at sustainablesources.com
[mailto:GSBN-bounces at sustainablesources.com] On Behalf Of Anthony Dente
Sent: 27 September 2013 10:45 PM
To: Global Straw Building Network
Subject: [GSBN] Straw Preservation in Clay _ Research Documents

Hello Everyone,

I hope your Septembers are coming to a pleasant close.  I'm curious if any
of you could point me in the direction of reports documenting the long term
preservation of straw in clay plasters, cob walls, or similar.  Most
importantly it's tensile characteristics.

I have been aware for some time of the "common knowledge" that wicking
qualities of clay's hydrophilic nature preserves such biodegradable
materials and that this is the backbone of many clay building techniques.  I
have even spoken with colleagues and friends who say they have chipped open
buildings and felt these qualities themselves.  Though I am unable to locate
studies/reports documenting significantly old structures (preferable in
rainy climates) that have had boring tests done and confirm this.

Thanks for any and all of your help,

Anthony

Anthony Dente, PE, LEED AP

Kevin Donahue Structural Engineers

Berkeley, CA

814.502.6001

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