[Strawbale] Bottom of wall detailing

[Jeff Ruppert]

Nick,

This is actually a very good question!  I have the book and can talk to 
the issues you address.

First, this detail came out of California and the detail masters out 
there.  In my opinion, it is not what I would refer to as a standard 
plaster detail that one would see on any other type of home.  Most of 
the time, plaster crews use J-strip or weep-screed to finish the bottom 
of their plaster. 

Second, this detail, in my opinion, is suited for extreme load-bearing 
conditions where you would want the plaster bearing directly on the 
foundation.  In the compression testing I recently posted to this forum 
about, we used weep-screed.  The capacities that were developed did not 
have the plaster resting on a foundation like this.  So if you want to 
do this, you may be able to develop greater load-bearing capacity, but 
the question then becomes, why?  If your wall is already twice as strong 
as a framed wall, are you loading it so much that you need that extra 
capacity, and if so, beware of what you are getting yourself into. 

I pulled this detail off the web very fast just to illustrate what I am 
talking about.  I take no responsibility for how complete it is or if it 
is correct in terms of flashing, but it shows a standard weep-screed.  
Many times we use J-strip, which is similar.  These types of flashing 
are available from stucco/plaster supply places like El-Rey. 

http://ppc.ucsc.edu/standards/details/07000/07.6-21.pdf

My point with all of this is, as bale wall builders, much of the time, 
we are reinventing details that have been used by the mainstream 
construction industry for years, and there are solutions that we are 
ignoring.  I have always told my crew, we are not "bale-stackers" or 
"straw dudes", we are plasterers.  Everything we do is about preparing 
our bale walls to receive plaster, or render.  All else is in service to 
that fact.  Start by researching how standard, well-done plaster details 
are put together and then revise from there.

As to the particular detail you ask about, I do not like it because it 
bonds the plaster to the foundation.  If there is any movement, it seems 
like a crack will develop along the top of the foundation.  This can be 
alleviated by using a bond-breaker, such as paper, or diesel ,or 
whatever to stop the plaster from actually bonding to the concrete 
foundation.  In my opinion, any moisture that makes it's way behind the 
plaster has no drainage plane for exit.  I prefer the flashing style of 
the J-strip or weep-screed.

Jeff "weeping screed" Ruppert, P.E.




N Leone wrote:
> Hello again. 
>
> Another question about a detail from Bruce King and Crew's Design of Strawbale Structures.  (Anyone get the impression that 1) I just finished reading that book, and 2) I'm in the "details" phase of my house design?)  On page 216, illustration 10D illustrates things to keep in mind when detailing the bottom of the wall, specifically in the "no earthquakes" areas.  The graphic shows the top outside corner of the grade beam notched down below the sill plate with the exterior plaster running down to that point as well.  The note referencing that area says "The outer plaster should sit on a shelf in the edge of the foundation below the sill plates..."  So my question is:  Why?  I know adding that notch to a poured grade beam might not be too hard, but it's going to be a bit of a mess on a block stemwall such as mine.  So I'd like to understand the reasoning behind it a little better to either 1) find an easier way to accomplish the same thing, or 2) be able to explain it to whatever poor sap (probably me...) has to make it happen in the block...
>
> Thanks,
> Nick
>   
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