[GSBN] lime plaster over compressed earth blocks
frank at livingsol.com
Fri Apr 4 06:40:40 CDT 2014
Here's a story that might help address your query, Bruce.
I agree with Graeme that design is the first solution. Design and plan
to keep the walls as dry as possible.
With climate change comes stronger, windier weather. Now we have to
plan on the walls becoming wind-blown with rain, (in between periods of
In addition to adequate roof overhangs, eavestroughs, and proper site
orientation, I do believe there is a good use for the magic of silicate
dispersion paints, either from Bioshields in the States, or Eco-House in
Canada. I'm certain there is an outlet in Europe, since that's where
that technology came from. I've used it a number of times, as a
colourant top dressing to plaster. The specs claim it to be vapour
permeable and water resistant, (Like gortex for plaster). I'm a skeptic,
so I prefer visual, tactile test results.
Here's an inadvertent, but likely valuable test result:
In 2004, we completed a straw bale home for a client in Ontario, Canada;
a climate of high humidity, and frequent rain through the Spring,
Summer, and Autumn.
Tina Therrien and Camel's Back Construction were on site, plastering,
when someone discovered that over the weekend Cheryl and I had both
quietly passed our birthdays.
Tina and her crew made two "birthday cakes" for us, out of the plaster.
They were so cute that we took them home, and set them on the deck to
When obtaining a series of samples of different colours of Eco-House
silicate dispersion paints, Cheryl decided to paint the "birthday cakes"
with a variety of these pastel paints, as a colour sample.
To make a short story longer, I set these samples out in the weather,
(in 2004), on the deck, where they have remained to this day. Slightly
chipped, and with the red colours slightly faded, these samples are
perfectly intact today. See the attachment photo of them, that I took
this morning ... yes, that's still three feet of snow in the background,
with a shovel handle sticking out as a depth gauge.
When it rains, the water beads up and runs off the surfaces of these
samples, and appears not to be soaking in. When covered with snow,
frost, ice, the samples have remained intact.
I've liked these "cakes", so I've never immersed them into a tub of
water, or attempted the "soak test" like Bill's friend, Paul Salas. I
think they would turn back into the plaster components that they came
from, and get pretty soggy. But standing up on the deck, in direct sun
and rain, they have survived over Ten Years.
So too have all the SB homes survived that we've treated with this
silicate paint over the past decade. It does wear, yes, and probably
will need a touch up coat after ten years.
It's no real replacement for good overall design, but I am a believer in
the help that they offer in the form of rainscreen cladding.
For what it is worth,
Living Sol ~ Building and Design
613 756 3884
for what it is worth
I have looked a many many walls treated with just about every magic
potion known to man where people have tried to remedy what really is
poor design in an attempt to try and reduce water ingress into earthen
materials. Small samples of some potions can give impressive short term
results, esp potassium silicate brews.
In nearly every case, when dealing with a whole real building over
several years, it also reduces moisture outfiltration (to reuse a great
word) and the very least result, in by far the majority of cases I have
looked at, is delamination of the treated surface layer, whether
stabilised or not, if not more severe degradation, or leaking issues.
If there already is a plaster delamination problem caused by moisture I
would not be brave enough to suggest that any magic potion alone will
The best performing surface treatments over natural earth are earth
plasters, but they are prone to erosion, closely followed by lime
plasters. Whitewash will also delaminate over natural earth.
Keeping most of that darn rain off with roof overhangs appropriately
sized for the conditions and /or rain screens is THE surefire treatment
that really works.
I really wish that there was a magic potion that really really worked.
And that I had $10 for every time someone had asked me to name them one.
Graeme North Architects
49 Matthew Road
tel/fax +64 (0)9 4259305
On 4/04/2014, at 1:54 PM, Bill Christensen <lists at sustainablesources.com
<mailto:lists at sustainablesources.com>> wrote:
Dang, I'm just catching up on my GSBN email tonight. Sorry we missed
you! Alert me directly next time, will you?
Paul Salas out of UNM told me about potassium silcate at one point, and
gave me a quick demo as we passed through Santa Fe one time. He was
looking into the same, and I believe he was trying to figure out if/how
it was chemically changing the soil. It was definitely effective in
reducing water problems - he had a small adobe that had been treated and
another of the same soil which hadn't, and when he dropped them both in
water the untreated one came apart. The treated one came out whole.
I suspect a brush-on application would help the plaster hang together as
a monolithic sheet. It would also reduce water infiltration, I
believe. Of course, it might also reduce outfiltration... If it holds
water in the untreated interior, well, I don't need to spell out for you
what could result. You're a smart guy.
On 3/26/14 9:59 AM, Bruce EBNet wrote:
I'm trying to help a builder near Austin, Texas with a delimitation
problem on a 7 year old building. He says he has since learned to use
potassium silicate as a brush-on stabilizer for the blocks, helps the
plaster hang on.
Austin folks: I'm coming into town tonight. Dinner?
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