[GSBN] lime over hessien

Derek Stearns Roff derek at unm.edu
Tue Apr 22 16:44:20 CDT 2014

I’m thinking that a two-story house that routinely faces 100km/hr winds isn’t the location where I would like to be gambling.  Many people posting have indicated that the clay plaster to lime plaster interface is a point of uncertainty.  There may not be an approach that is both inexpensive and reliable.  Building a ventilated rain screen system for the whole wall system would be expensive, but has the potential to be reliable.  Using only lime plaster would be more expensive than applying a body coat of clay, but it would increase my confidence.

Andy Horn prepared a very interesting PDF on a lime/clay/dung plaster that was in use 100 years ago in South Africa.  He has pictures that document great weather resistance in weather-exposed uses.  Recent postings from Deva and Harry Francis via Rob Tom point out that applying lime plaster on top of clay/lime plaster may be more reliable than lime over clay.  Perhaps lime plaster over Andy Horn’s lime/clay/dung plaster would be worth some testing.

Two years ago, I posted Andy's 2 MB PDF on the site of the 2012 ISBC, but I’m not sure if it is still available.  The link below will let you download it, if you are interested.  I will leave this link up for a couple of weeks.



On Apr 22, 2014, at 10:02 AM, Kyle Holzhueter <nihondaigaku.kairu at gmail.com<mailto:nihondaigaku.kairu at gmail.com>> wrote:


In Japan, there is a several hundred year history of applying Shikkui lime plaster over earthen walls. Further details are available at the links below, but I wanted to point out a couple prominent features:
1. Addition of seaweed glue to improve adhesion and moisture retention
2. Minimal sand is used, which reduces the weight of the plaster and improves adhesion to the earthen plaster.
3. Addition of hemp fibers to improve flexibility and bending strength
4. Depending on the level of exposure, Shikkui finishes are expected to last about 20 years. Exposed walls will experience delamination earlier, protected walls will stay in good condition much longer. In this sense, the Shikkui finish is a kind of sacrificial layer.

You might find the following links helpful:

Yours in mud,

Derek Roff
derek at unm.edu<mailto:derek at unm.edu>

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