[Cob] Lime Render - FAILURE

[Shannon Dealy]

On Fri, 17 Feb 2017, Bill Wright wrote:

[snip]
> I've listed the brown and finish coats here previously, and the wall in 
> question is a 100% cob wall. What IS there as well, helping form the 
> curve in the wall, and helping the cob/brown coat/finish lime coat 
> connect to the framing for the doors is. . . Expanded Metal Lathe. So 
> the layers in sum are: Cob wall, expanded metal lathe bridging the 
> wooden door frame to about 12" onto the cob wall, and screwed into the 
> cob wall w/ 3.5" deck screws, brown coat, finish lime render.
[snip]

One additional thought, look at the areas which aren't showing signs of 
cracking/flaking. Presumably this is the majority of your building? If so, 
think of these as places where you got the job done correctly and ask 
yourself what are the differences between those areas and the places where 
you are having problems. Your issues may not be current issues, but may 
have happened during the initial application and simply taken time to 
become visible.

Things to consider might include:

  - Differences in the wall surface under the plaster  (such as the metal
    lathe - I've never used it so I have no idea what, if any issues it
    might raise)

  - Differences in airflow patterns across the building. Areas exposed to
    prevailing winds or just unusual wind patterns at the time of
    application may end up drying much faster than more protected parts of
    the building, which can cause the problems you are seeing.

  - Differences in sun exposure which can also cause drying to be too fast.
    This difference doesn't have to be how the sun hits the building such
    as North versus South side (though it may be), it could simply be the
    time of day in which the application was performed.  If you applied in
    mid day sun versus evening.

  - Differences in how you protected the surface after application such as
    misting the area periodically, hanging a tarp over it, etc.  Perhaps
    some days you had to leave the site immediately where for others you
    were around for a while to keep the new plaster moist.

  - Finally (typical of my work :-) seasonal differences if you do the job
    piecemeal, completing part of it in one application, then becoming too
    busy so the next part was done weeks or months later when the humidity
    or other environmental factors are different.

FWIW.

Shannon C. Dealy               |       DeaTech Research Inc.
dealy at deatech.com              | Biotechnology Development Services
Telephone USA: +1 541-929-4089 |      USA and the Netherlands
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