Re: Cement Stucco vs. Earth Plaster

[Kurt Rathmann <rath9362@uidaho.edu>]

> Hi Dion,

I've used exterior cement stucco on several projects now with success.
I've experienced no 'problems' during application or later that could be
attributed to the use of strawbales as a substrate with the exception that
you need to use more material  due to thickness and that it can be tricky
to calculate the amount you will need to complete the job.  I've used a few
different mixes from a cement rich 1 sack cement, 1/2 sack lime plus
Pozalite (just a little according to manufacturer's instructions) and about
37-40 shovelfuls of sand to a lime rich  1 sack cement, 3 sacks lime and
45-50 shovelfuls of sand.  The latter created a softer stucco while the
former was very, very hard.  The lime-rich mix has been in service now for
5 years with no cracking while the cement rich mixes I've used do have some
normal shrinkage cracks but will provide years of maintenance free
service.  I also use fibers in the mix as well as meticulous prepwork
(flashings, stucco netting over 'field', expanded metal lath at
edges/dissimilar material laps).  Slowing the cure is also important.
Whenever possible I schedule the stucco application during October/November
here when the weather is 'just right' - overcast, misty rain, cool temps.
This way I don't have to tent or spray the walls.

I've never used any type of breathable coating, paint, or water repellents
(yet) over the cement stucco and have used either ferrous sulphate or
mineral oxide pigments for color.  In our area, freeze-thaw cycles are
frequent, so I design to minimize exposure of the vertical surfaces to
weather, and will not expose the horizontal surfaces (landscape walls
etc.).  I'm also critical of splash zones and either increase the overhang,
install gutters, or use some other type of wall system.  All of my designs
are some type of hybrid - not pure sb.  The last project was a combination
of Rastra with an acrylic stucco (exposure and splash), stick frame and
metal siding (geometrically ill-suited to bale construction, or to maximize
usable space) and straw bale infill with exterior cement stucco and
interior gypsum plaster.

So, depending on the site, design, climate, etc. choose your system
accordingly...

Kurt Rathmann
3 Little Pigs Design-Build
Moscow, Idaho



> I am leaning towards cement stucco because I do not want constant
> >maintenance.  Have there been any problems with cement stuccos on
> >strawbale that people are aware of?  I am not concerned with cement
> >stucco that was done improperly, I mean with properly applied cement
> >stucco.