[GSBN] lime over hessien/ Cement Lime.

Derek Stearns Roff derek at unm.edu
Tue Apr 29 13:52:37 CDT 2014

Can you say more about your concerns, Sven?  Given that mixes of roughly 0:1:3 (Portland cement:lime:sand) have been used successfully for more than 2000 years, and many of these structures are still in existence, it’s clear that Portland cement isn’t a requirement for durability.  Of course, it has pluses and minuses.


On Apr 29, 2014, at 9:05 AM, Misha Rauchwerger <misha.rauchwerger at gmail.com<mailto:misha.rauchwerger at gmail.com>> wrote:

We used a Natural Hydraulic Lime on straw bale mix of 1:2:9 (cement:Lime:sand) with good results

Misha Rauchwerger

On Fri, Apr 25, 2014 at 11:04 AM, Sarah Johnston <sol_design at yahoo.com<mailto:sol_design at yahoo.com>> wrote:
Thank you to all who gave input on this subject!

Further talks with the client have led to a full vented cavity for this project which means there is no Hessian involved any more.  They want to hang plaster on the exterior so they will still be having some challenges in their conditions but the straw will be well protected even if they have plaster failures.

What mixes for lime cement are people using?  I believe Chris Magwood has gone as far as a 1 cement 3 lime and achieved good results.  Are others getting positive, durable results from mixes with low cement ratios?

 Sven Johnston
Sol Design, Ltd.
50A Connolly Street
Geraldine 7930  New Zealand
03 693 7369
sol_design at yahoo.com<mailto:sol_design at yahoo.com>

From: Derek Stearns Roff <derek at unm.edu<mailto:derek at unm.edu>>
To: Global Straw Building Network <GSBN at sustainablesources.com<mailto:GSBN at sustainablesources.com>>
Sent: Wednesday, 23 April 2014 9:44 AM
Subject: Re: [GSBN] lime over hessien

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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