[GSBN] lime over hessien

ejgeorge at riseup.net ejgeorge at riseup.net
Thu Apr 17 07:55:35 CDT 2014

Hi Sarah,

Couple of comments --

One issue would be the tightness/looseness of the weave of the hessian  
wrap. We've similarly tried using a loose weave burlap as a key, and  
discovered it took a lot of effort to actually force the plaster  
through the gaps. Despite due diligence in doing so, when removing a  
plastered wall section for an addition several years ago, we  
discovered that the burlap created a weak bond between layers.

Maybe a really loose weave could work - we've switched to a very thin  
1" poly mesh (known in these parts as "deer netting") which allows for  
much better keying, though it is unfortunately plastic so wouldn't  
provide the moisture component they're seeking.

Another concern would be the potential slumping from the weight of all  
that wet plaster.  We like to let the bulk of the moisture come out of  
the clay base coat and then add it back in on the surface with a hose  
to get the moisture level that seems appropriate for the season and  
site.  In our climate, when we have had issues with a 2nd and finish  
lime plaster coat not carbonating properly it has been from excess  
moisture typically at the bottom of the wall.  Tall walls are  
particularly problematic for us with moisture moving downward and  
keeping the bottom of the wall too wet.

As far as keeping the lime from drying too fast, we have experimented  
with completely tarping in the plaster and using irrigation misters to  
provide humidity. Our climate sounds much less extreme than your  
client's, and as mentioned, our main challenge became dealing with  
managing too much moisture with this set up and so we have mostly  
returned to the tarp-it-in-and-mist-with-a-hose-as-needed method - but  
if we had a particularly hot/dry summer with a wind-exposed site we  
would definitely return to the misters.

Good luck!


ej George, CSBA
Tugley Wood Timberframing

Quoting Sarah Johnston <sol_design at yahoo.com>:

> Greetings All,
> We have clients who are in a predominantly very dry, windy climate  
> with temperature extremes from 40C to -18C wanting to adapt the lime  
> over clay plaster system we generally specify.  
> They are wanting to apply the 30mm 'body coat' (approximately  
> 1clay;1sand;1straw) and immediately apply a clay slip soaked  
> hessien/jute/burlap wrap around the entire home which is two story.  
>  While still wet they are wanting to wire brush the hessian to  
> create a key, apply another clay slip then 10mm of lime plaster.
> The application of clay slip over the hessien seems like a bad idea  
> to us but we can see the draw to being able to apply the lime over a  
> wet substrate in their climate as trying to keep the lime from  
> drying too fast is a real issue for them.
> We have a colleague who has used this technique two times in their  
> area but both projects have been up less than a year.  We have no  
> personal experience with this technique and are hesitant to write a  
> specification....  
> Can anyone give a history lesson?  I know there was an article in  
> the Last Straw some time ago.  Anyone still using this concept?
> Any input would be great!  
> Cheers, 
> Sven and Sarah Johnston 
> Sol Design, Ltd.
> Geraldine 7930  New Zealand
> 03 693 7369
> sol_design at yahoo.com
> www.soldesign.co.nz

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