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Re: GBlist: Re: Stucco

A quick note on breathability and latex/acrylic mediums. I came upon a
reference for a european iaq research project that focused on mold
growth between layers of latex paint (bathroom area focus) and between
drywall and latex. Anyone familiar with this study or similar ones.

John Salmen

Buzz Burrell wrote:
> On 9/5/97 12:00 AM Joyce Coppinger wrote:
> >What polymers are used or can be used in stucco products used for
> >strawbale construction?  Concern is for breathable wall which won't
> >crack over time because of climatic conditions (freeze and thaw
> cycles,
> >moisture, hot to cold climatic changes). What types of stucco
> products
> >are available using "natural" ingredients which would have the same
> or
> >similar properties as stucco or coatings with polymers?
> I've spent a bit of time researching stucco, and I still know
> amazingly
> little about this important material.  I would like to hear other's
> replies.
> First some terms, all of which apply to the Southwest only, and are
> totally casual and unofficial.   "Stucco" tends to mean whatever is
> applied to the exterior, and "plaster" means its on the interior.
> Whats
> called "traditional" stucco is cementitious;   its usually applied in
> 3
> coats ("scratch", "brown", and "color").  Of course, this isn't
> traditional at all;  that would be mud.  The word is used to
> differentiate from the acrylics, such as Dry-Vit, etc, which are
> essentially heavy duty paints.  I have no idea what you might mean by
> a
> "polymer", unless it was mistaken for acrylic, or is one of the roof
> coating products more common in commercial and industrial
> construction.
> So there are three general residential classes of stucco:  1. mud;  2.
> cement;  3. synthetic (acrylic).
> These are often mixed together.  For example, it is rare for someone
> today to use a pure mud;  it is usually "stabilized" with a percentage
> of
> cement.  Thus, there is a huge range of possibilities, plus all the
> additives to the above (cactus juice, horse hair, sheep blood, etc).
> A
> fun treatment is to use a cementitious stucco, but utilizing sand from
> your site for the mix;  thus you get a truly harmonious color scheme.
> In practice however, I think the choices narrow to something much more
> manageable.  Straw bale requires 3 coats, due to the gaps to fill,
> which
> mandates either a mud/cement or cement base.  Then the color coat can
> be
> either acrylic or cementitous.  Frankly, I think this is simply
> personal
> choice;  they both work fine.
> Which brings us back to your question regarding "a breathable wall
> which
> won't
> crack over time".
> I find this "breathable" question somewhat annoying, in part because I
> don't know enough myself, in part because I think its a false alarm,
> and
> in part because I suspect it doesn't matter.
> 1. If its cementitious or mud, it will crack, and often not over very
> much time.  Guaranteed.  If a stucco doesn't crack, then its not a
> "natural" product.  Sorry about that.  The mud stucco's were usually
> refinished on a regular basis.  The hairline cracks in the cementitous
> products are considered to be a cosmetic issue only.  The acrylics
> stretch and cover the hairline cracks in the underlying basecoats.
> 2. Personally, I wonder how much the two differ in breathability
> anyway.
> Imagine being inside a sealed room with no openings, with one encased
> in
> 3/4" of concrete, and the other encased in the same with an 1/8" of
> paint
> on top.  I think you would suffocate in either one.  Maybe not though;
> I
> would love to hear the air transmission ratings for these different
> stucco products from a more technically proficient list subscriber.
> 3. At any rate, "breathability" in walls seems easily achieved by
> opening
> a window.
> The house is what needs to breath.  (How much air diffusion is optimal
> for a wall is a very complicated and controversial separate issue.
> Its
> much easier to install an HRV than it is to waste valuable brain time
> by
> studying the problem).
> Probably the most common treatment in the SW, is to use a cementitious
> basecoat (2 for strawbale or adobe, 1 coat for anything else), that
> has
> fiberglass mixed in for cracking resistance (required by code if doing
> a
> single base coat).  Then an acrylic is used for the color coat.
> Good luck on this one.
> Buzz Burrell           "Time flies like an arrow,
> Boulder, CO             Fruit flies like a banana".
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