[GSBN] Lime plaster and expansion joints

[Laura Bartels]

Bill,

Thanks for your thoughts.

A comment to throw in related to yours below...

> As for straw bale buildings in general I've always been amazed how  
> prevalent cracking can be with cementitious coats.  Sometime back we  
> did some experiments because I got to thinking that one of the major  
> causes was the highly uneven thickness that can happen with the  
> scratch coat. I don't think it would be an exaggeration to say that  
> in some cases, depending upon the joints between the bales, the way  
> the bales have been stacked, etc. etc. the thickness of the scratch  
> coat can range anywhere from 1 to 4 inches making it highly  
> susceptible to cracking.  I mean you would never do that with any  
> other type of wall, at least I wouldn't.  Therefore, we adopted the  
> strategy of filling out all cavities and low spots in the wall so  
> that the base or scratch coat was of similar thickness.  That has  
> always worked well for us and was what our Mexican friends did on  
> the building I mentioned above.


A year or so ago I went back to look closely at cracks that had  
developed in various places on the walls of the Waldorf School  
buildings. Some areas on two of the buildings were through all three  
coats of cement stucco. As I was doing a bit of moisture investigating  
as well (including drilling in places that there was no cracking but  
in areas that were going to be re-touched anyway, I was probing all  
the areas I could. What was significant was that there seemed to be a  
correlation between where the probe had little resistance and where  
the largest cracks were. It appeared that in areas where the straw was  
not firm and voids not well stuffed or filled, that it allowed more  
cracking. Now, what the exact explanation is I'm not sure- temperature  
variations causing cracking, thicker stucco in those spots as you say  
above, etc. But what seemed clear was that correlation.

These conversations are making me wonder how we collect more of  
people's experiences relating to things like this, compare them,  
examine them, and learn more from all that we collectively are doing.  
Some of you write books, some are very active on this and other lists,  
some do master's theses, some keep very detailed observations...  
occasionally we wrangle up some money to do formal testing. It's all  
critical work. Am I off my rocker to think that there may be some way  
to throw our lessons learned into a database with sections on various  
topics, describe as many of the variables as we can, and over time  
watch for congruences and incongruences? Could it be this same group  
done privately, to give us a chance to chew on all sorts of things?  
Maybe its just perhaps another use of this exact same format. Maybe we  
raise topics periodically- lime plaster, earth plaster, plaster prep,  
structural systems, etc.

Thanks for your indulgence in my thoughts...

Laura - always wondering - Bartels