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GSBN: Lime plaster problems



<x-charset windows-1250>Dear all

Dear all
I know this is not strictly a SB question, but rather one of lime plaster
...but really could do with some experienced input.

I recently was involved in the building of a large 2 storey mud brick school
classroom...in a rural part of the country. To help protect the walls we
applied an earth plaster followed by a coat of lime plaster on the weather
side. We used a hydrated lime and added plaster sand together with a small
amount of the adobe soil to the mix. We applied the plaster and as soon as
it had set applied a colour "fresco" wash for a gorgeous looking finish. We
also rewet the wall continuously for good curing, but were not equipped with
proper scaffolds and drop sheets to cover the walls from the sun and wind
...and made do with a large sail that was precariously positioned around our
2 scaffold towers.

While applying the plaster, we ran into a number of difficulties. The wind
suddenly picked up and was drying the plaster out excessively quickly,
leading to much cracking. So we had to rework the cracked surfaces to get
the cracks out. On the first morning after applying the plaster the weather
turned at night and brought frost...2 months ahead of when it is normally
expected! There were sheets of ice in the water buckets that morning!

A few weeks later, it turned out there were major problems with the plaster
delaminating from the walls, (see below).

The supervising architect wants to know what to do....and is being advised
to strip off the existing plaster and attach a chicken mesh around the
structure and reapply the lime plaster. I am not keen using the
mesh....don't think it is needed if there is no cement in the plaster. Also
it can rust and will be expensive. The whole idea with the project was to
train the locals in simple inexpensive methods they can employ on their own
structures.

If anyone has some insights to share or advice as to how we can do it
better, I would most appreciate your inputs. Maybe we should have done 2
coats....The base earth plaster coat was due to a miscommunication on site
was not provided with a proper key....and we were not sure how to provide
one with the earth plaster already hardened, without damaging / impairing
its strength. Any ideas for how best to do this....drill holes, angle grind,
soften with water and saw cuts...???
I also have pictures I can email to you directly if you want to get a better
idea of the problem we are facing

Your inputs would be much appreciated

Kind regards
Andy Horn
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Hi Andy

Here are some photos taken earlier today of Block B.

Owen, Dave Osborn &amp; I all agree that there doesn't appear to have been a
proper bond between the lime plaster and the earth plaster. The surface
treatment of the substrate appears to be too smooth for bonding to take
place. The bad news is that there are large 'hollow' areas - at least 50% of
the plastered surface. We all agreed that a good solution would be to strip
the plaster off and nail/staple a layer chicken wire onto the substrate
before replastering. I guess that we should have scratched the surface
deeper before we applied the plaster. Weather conditions could also have
played a role. The lime plaster layer is approximately 10mm thick and
appears to be strong.
Please give me your thoughts on this.

Regards

Steve




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