[Strawbale] Hydraulic vs. Hydrated Lime

[Andrew deGruchy]

Bale-On dudes! This is my first time ever posting a communication on one of
these bulletin boards. I hope it works and tell me if this is too long. I
get long winded about lime.

Anyway, I was talking with Michel Couvreux the other day and he said I
should check out this strawbale community sounding board especially since I
might be able to help with the Hydraulic Lime vs, Hydrated Lime or cement
stucco issues. I hope I can. I really have my experience in historical
masonry building restoration but there is a cross-over to sustainable
construction especially regarding lime.

Which lime?, what is lime?, what does it do?, when do you use it?  and how
to get it cheap are some of the first cross-over points.
I see that David Elfstrom of Toronto mentioned my interview with the Chicago
Tribune/Washington Post about lime, which I posted at
http://www.palimeworks.com/lwus/Infoall.html. Thanks. It took a long time
for me to understand lime, about 18 years as a mason using type S hydrate,
before I really understood the chemistry and found out about NHL. Really we
all have been in the dark about this mysterious and wonderful material for
millennia. Chemistry as we know it as a science really only asked the
questions of what things were and why they work on a molecular level
starting in the mid 1700's. But masons, even though they didn't know how to
chemically describe it, just knew from trial and error over thousand of
years, how it works and how to work it. There is no substitute for just
getting your paws on it.

That is what I did at the International Straw Bale Builder's Conf. in
Lakefield, Ontario. I just brought some St. Astier NHL and pigments, mixed
up 8 or 9 colors of finish plaster and let the artists in attendance play on
the base coat first applied. I brought up the NHL in my truck, from PA, and
wasn't sure how the group wanted me to run a workshop, so I just brought my
spray gun and some Harling trowels and we demonstrated spraying the lime and
then throwing (Harling- sounds like hurling because that is what it is), the
lime plaster with 3/8" gravel in it at the bale building that was already in
place at camp Kawartha. We only had enough material to do this to a small
section.

I did not realize that the intent was to plaster the whole building during
the week long event. That is what was accomplished using other techniques of
placement and using a masonry cement /lime/sand mix. Masonry cement is only
Portland cement with crushed limestone in it as a kind of filler. It does
help cushion the movement along with air entrainers and other additives
present in some masonry cements. So, I agree that it is something that some
people have found gives what appears to be good results. It is better than
Portland cement and type s hydrated lime and sand in my opinion, but still
way off from what is optimal. I see optimal meaning that you never have to
do it again or have related consequences inside the building because of what
you did outside. I don't know if they will have to do it again prematurely,
but cracks means water and water means rot. I did not see cracks in the
freshly placed masonry cement/lime stucco during the time I was at the camp.

Anyway, the thing that I did that made attendees who were sitting there
listening to my lecture, open mouths agape and fall off their bale, was when
I showed the 12" x 18" masonite board (1/4" thick) which I had previously
applied a 1 white Portland cement, 2 Type S hydrated lime and 9 sand mixture
to as a demonstration of what is considered a "high (type s) lime content"
mortar gauged for strength and durability with a little Portland cement and
bent it to an arc before there eyes.

When I bent the board to form an arc the plaster cracked every inch or two
along the whole board as would be expected. By the way, around the camp I
noticed that the plaster on the already existing strawbale buildings had
vertical cracks in places that were evident though not as many since no one
was bending the building to an arc.

Back to my lecture and demo:

Everyone sips their green tea, yawned and thought, "boring" "Who is this
nut?" Then I took out another identical board with a pure 1:1 lime and fine
sand mix previously placed on the board weeks earlier, at the same time I
made the lime/cement/sand board. I bent it to an arc compressing it as far
as I could bend it without breaking the board. No cracks. It flexed
beautifully. One guy in the group raised his hand and screamed "SOLD" when
he saw it. Since Portland cement has a needle-like crystal structure it is
brittle and breaks on the needles. Lime has a hexagonal plate crystal
structure and the plates lay all over on top of one another and shift
between one another allowing for movement. Lime already is the ultimate flex
material. You don't need to add anything to make it more flexible.

NHL 2 and St. Astier EcoMortar mixed 1:1 for a finish coat, (or NHL 2 and my
Ecologic Mortar that I am blending in Pennsylvania to St. Astier specs using
local sand), has this beautiful flow like historic lime plaster and both
moves with the building and has incredibly long (days) of working time
depending on how you control humidity. Here's some of the art that was done
at the strawbale builder's conference with this finish plaster mix :
http://www.palimeworks.com/lwus/venplasters.html.

My advise to everyone is to get a small amount of these materials and work
with them. Just like when you are going to use a cleaner you are supposed to
try it first on an inconspicuous spot and then go for the whole area when
you know it works and how to work it,  do the same with the lime. There is
no substitute for personal experience.

All of what you will get regarding performance in the form of numbers is
posted on St. Astier's website. www.stastier.com. So, if you want to get
known values for the comfort of knowing what to expect in what you also like
using then St. Astier NHL or someone's product who will tell you that data
is what you need. You also always need a caring installer who knows how to
stucco and plaster. There can be failures of the best material if put into
the wrong hands.

If your building is more an outbuilding or temporary structure you can
experiment with low temp fired high calcium type s hydrate that you can find
somewhere within 500 miles of where you live. You can doctor it up, (just
stay away from Portland cements to speed the set). One way to "Doctor it" is
by using low temp fired brick dust from recycling historic brick by grinding
them up to a fine powder. This will give your pure hi-cal lime a hydraulic
set for a faster setting time than just waiting the weeks it will take for
regular hi-cal type s hydrate to set up between coats by exposure to the
air. Ordinary Type S Dolomitic Lime burned in a rotary kiln above 2000
degreed F is not the base local lime you want to use for this experiment,
even if it is easily obtainable, to save you time, frustration and failure
in this attempt to "brew your own." In my opinion use High Calcium Type S
hydrate and ask the manufacturer if it was burned under 2000F.

One final note- When you are doctoring up your locally available hi-cal,
low-temp fired, type s hydrated lime, you will not have definitive numbers
of the final strength, modulus of elasticity, liquid and vapor permeability
unless you have the material sent to a lab for testing. So it is risky to
apply any shelter coat to a valued strawbale building if you don't know in
advance what it will do for the long haul. The lime plaster walls are a huge
part of the exterior envelope that in my opinion should not be compromised.

Sincerely,

Andrew L. deGruchy
Owner/Consultant
Lime Works.US
P.O. Box 151
Milford Square, PA 18935
www.limeworks.us
Technical help phone 215-536-6706
e-mail: begreen at limeworks.us

Material Order only:
Attn: Jim Plante
Phone: 215-536-6706
Fax: 215-536-2281
e-mail: order at limeworks.us