[GSBN] lime over hessien/ Cement Lime.

Ian Redfern ian at adobesouth.co.nz
Tue Apr 29 16:47:33 CDT 2014

Good morning Sven,Derek and All,

The use of cement is to have an early "go hard" element to the plaster for
speed of lay up only ­ there is a downside to using too much cement as
indicated by you Sven in so far as it "holds" free water in the matrix which
we can safely assume to induce rotting (as we see when timbers contact
concrete)  AND  a huge reduction in vapor permeability ALSO an increase in
water transport through the plaster  i.e. It is not desirable and literature
shows that a maximum is 1 : 3 : 9  cement : hydrated lime (lime putty is
preferred) : sands (clean sharp non pozolanic)  we used on the Canada
project  1 : 1: 9  plasterers lime (50% cement 50% lime powder) : hydrated
lime (fresh builders lime powder) : sharp sand  which worked well.  -  this
stuff ail still crack if laid up too wet and  allowed to drying to fast !

I mention pozolanic sands and soils as here in New Zealand with its active
geological belts we find great soils near volcanoes (parts of Northland)
and sands which are washed out flood plains from old volcanoes (Waikato and
surrounding plains)   where the sands naturally induce a "hydraulic"
reaction with the lime putty (i.e. They cure under water although rather
slower than portland cements)

In conclusion :
1)  I recommend  wrapping the building with a wind stop (as we see here
around Auckland) for leaky building remediation where the scaffolding is
enclosed in a vapor permeable and translucent plastic wrap and all work is
protected from  rain, wind, and cold temperatures  -  plasters do not
perform if subject to freeze  (10oC and below) which includes hyperthermic
consideration of cold and/or strong winds swirling around the building
2) use a lime putty and sands plaster ­ mix the sand sizes for greater bind
and strength (5 mm down)

  www.adobesouth.co.nz   Ian Redfern
 Adobe South
 A:    5 Lancewood Rise, Onerahi, Whangarei
 P:     09 436 4040      M: 027 490 2324
 E:     ian at adobesouth.co.nz

From:  Sarah Johnston <sol_design at yahoo.com>
Reply-To:  Sarah Johnston <sol_design at yahoo.com>, Global Straw Building
Network <GSBN at sustainablesources.com>
Date:  Wednesday, April 30, 2014 9:12 AM
To:  Global Straw Building Network <GSBN at sustainablesources.com>
Subject:  Re: [GSBN] lime over hessien/ Cement Lime.

Good question Derek.  The concern was aired by a friend who had read
(somewhere) that the most reliable mixes either had no cement or at least
equal portions of cement and lime.....  I do not know why, thus my asking.

Perhaps it is due to the lime not being cured well if the plaster sets
'quickly' due to the cement portion and the plaster not being kept moist
long enough for the lime to cure?  More an application issue than a mix
issue...?  This is assuming my understanding is correct that the lime does
not become pozzolanic but is still standard calcium hydroxide trapped in the
hardened cement.  

We are working with calcium hydroxide as we can not buy NHL here in NZ.
> 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, it¹s clear that
> Portland cement isn¹t a requirement for durability.  Of course, it has pluses
> and minuses.  
> Derek
> On Apr 29, 2014, at 9:05 AM, Misha Rauchwerger <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
>> BuiltInBliss.com <http://BuiltInBliss.com/>
>> On Fri, Apr 25, 2014 at 11:04 AM, Sarah Johnston <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
>>> www.soldesign.co.nz <http://www.soldesign.co.nz/>
>>>> From: Derek Stearns Roff <derek at unm.edu>
>>>> To: Global Straw Building Network <GSBN at sustainablesources.com>
>>>> Sent: Wednesday, 23 April 2014 9:44 AM
>>>> Subject: Re: [GSBN] lime over hessien
>>>> I¹m thinking that a two-story house that routinely faces 100km/hr winds
>>>> isn¹t 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 Horn¹s 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
>>>> I¹m 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.  
>>>> https://www.dropbox.com/s/o42bruzrxim5cc5/Andy%20Horn%20Herbert%20Lime-Dung
>>>> %20Plaster.pdf
>>>> Derek
>>>> On Apr 22, 2014, at 10:02 AM, Kyle Holzhueter
>>>> <nihondaigaku.kairu at gmail.com> wrote:
>>>>> Hello,
>>>>> 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:
>>>>> http://japaneseplastering.blogspot.jp/2014/02/shikkui-plaster-mixing-and-a
>>>>> pplication.html
>>>>> http://japaneseplastering.blogspot.jp/p/blog-page_25.html
>>>>> Yours in mud,
>>>>> Kyle
>>>> Derek Roff
>>>> derek at unm.edu
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> Derek Roff
> derek at unm.edu
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