[GSBN] Lime plaster and expansion joints
brian at anvill.com.au
Sun Feb 8 20:03:08 CST 2009
Hi to all,
We originally had this problem, but found that by fixing stiff wire netting
(40mm hole x 1.4mm thick wire) to the face of the bales adjoining the posts,
with a small amount of straw between the post and the wire netting, this
problem was virtually eliminated. It is not that we don't get any surface
cracking at all, but it does not follow the line of the posts, and is
generally only one coat deep. Allow the wire netting to overlap the bales by
about 200mm (8"). This can be fixed to the bales either using wire pins or
by stitching it to the bales with twine if extra strength is required. When
rendering, ensure that the first coat of render is not too deep, but is a
surface bond only. This will allow the straw to act as a barrier between the
post and the wire netting. We are based in Central Victoria Australia which
is hot and dry so I can't say what the results might be in more humid areas,
but it might be worth a try.
We have also been experimenting with rice flour past mixed with powdered
clay or lime with water added to create a paint like consistency. This is
sponged over the final coat of earthen render. The earthen render has approx
10% lime. This seems to be providing greater weather resistance, and at this
point appears to be more elastic, thereby giving extra resistance to
cracking with temperature changes. We have recently had 24 degree centigrade
at night with 46.5 degrees during the day. Which is what lead to our
dreadful fires with so many deaths. (108 current count).
I would be interested to know if anyone else has experimented with such a
coating. We have now had it on a house for about 12 months, and expect to
try it on another shortly. We will also be applying it to my office, which
has been built with no eave protection to the south, so that we can really
test its weather resistance.
I hope this helps,
----- Original Message -----
From: "Jeff Ruppert" <jeff at odiseanet.com>
To: "(private, with public archives) Global Straw Building Network"
<GSBN at greenbuilder.com>
Sent: Monday, February 09, 2009 4:09 AM
Subject: Re: [GSBN] Lime plaster and expansion joints
> The horse arena that we built near you has had more cracking on the
> exterior walls than I expected. We placed regular expansion joints on
> every post, which were roughly 20 feet apart. The frame was steel.
> In looking at the cracks it seems that the expansion of the frame in a
> vertical direction places the panel in tension and creates the cracks.
> The vertical expansion joints don't do anything for this action.
> The interior plaster on the same walls do not show many cracks. The frame
> is against the exterior face of the wall and the mesh was attached to the
> The interior bale walls on the same project which are not exposed to the
> extremes of the weather have not cracked.
> In doing it over I would have found a way to not attach the plaster to the
> frame. I am not sure how this could have been done easily, but steel
> frames expand and contract with temperature so much that attaching a rigid
> material like plaster to it can be problematic. Maybe horizontal joints
> would have helped a little, but I doubt it. From the appearance of things
> the magnitude of expansion and contraction was just too much for any type
> of plaster to deal with. I would expect the same to happen with both
> earth and lime, unless you make them elastic or tell the to stretch when
> it gets hot.
> If your frame is wood these issues are going to be easier to deal with.
> Jeff Ruppert
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> GSBN at greenbuilder.com
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