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Re: GSBN: Lime plaster problems


It seems to me that major problems were weather related, the drying wind and
freezing. You don't say just how smooth the earth plaster was before lime
was applied. If it's a porous material the lime would be able to adhere even
without scarfing.

The lime plaster needs to be removed in any case, and you could no doubt get
some teenagers to deface the surface of the earth plaster for a small fee.
Then try again in warm weather, or move the building south to a warmer


On 9/26/07, Andy Horn andy@... wrote:
> 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
> ----------------------------------------------------------------------------
> --------
> Hi Andy
> Here are some photos taken earlier today of Block B.
> Owen, Dave Osborn & 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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> 08:02 AM


John Swearingen
Skillful Means, Inc.
Design and Construction

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