Note from Charmaine: I kept this email from 1999 as an excellent
overview of using the Pickly Pear in plasters... reprinted with
permission.. I believe the book he refers to is the old "The StrawBale
House" now replaced with more up to date books and advanced building
methods for bales. The plaster info remains as useful.
Date: Wed, 26 May 1999 12:30:08 -0700 << sent to Papercreters almost
exactly 9 years to the day he posted this!!!
Subject: Re: Prickly Pear In Plaster References
From: "Athena & Bill Steen" <absteen@dakotacom.net>
Prickley pear cactus gel has been used in Mexico for centuries
primarily as a stabilizer for lime plasters and to a much lesser degree
with earthen plasters. It has been used with lime in a great variety
of ways and up til now we have not really been able to identify the
differences between these methods.
*****However, important to note is that there are many varieties of
prickley pear cactus and all do not perform equally. In Mexico, we
have found a great deal of variance in the peformance of these plants,
both in the amount of gel they contain and secondly the stickiness of
the gel.
The other variable is that there are numerous varieties in the
southwestern U.S. and Mexico that grow quite tall and produce a large
volume of plant material making it quite easy to harvest enough pads
for a project in contrast to the low growing varieties of northern
climates.
1 - At times, quicklime has been slaked in water that contained
prickley pear gel and then used as a putty to mix plasters, mortars and
limewashes.
2 - It has also been used by adding the gel to plaster mixes that are
prepared from normally slaked lime putty and sand. 3 - It was recently
used in the restoration of an old mission in Tucson, AZ by mixing dry
lime (powdered) hydrate with prickley pear gel and water. This method
is less common in Mexico and seems to be most useful in bringing poorer
quality dry hydrated lime to a level of good performance and
workability.
The gel is prepared usually in one or two ways in Mexico/Tucson, but
has been using other methods as well. One method is to chop up the
pads of the cactus and soak them in water for somewhere between 1 to 2
weeks. The process involves filling a container with the pads and then
topping it off with water. The gel that is produced is usually diluted
with 3 to 4 parts water and then used to mix the lime with aggregate.
If the lime is already in putty form that was prepared with plain
water, it is usually diluted less. If using this method, be prepared
for a strong odor that is produced at the completion of the soaking
time that is not particularly relished by most.
The second process is to chop up the leaves and boil them in water and
then use some type of press to extract the gel from the chopped up
leaves. Boiling time is critical as too little time does not allow the
juice to be extracted and too much boiling causes it to be diminished.
A mop press makes a convenient tool in this method. Like the above,
the gel that is extracted is diluted with 3 to 4 parts water. The
water that was used to boil the pads can be used for dilution. No odor
using this process.
However, the use of the gel with plaster is much less common than using
it with limewash. That is the most common use of the plant to this
day. It is usually used in a mixture that contains lime, water, salt,
alum, prickley pear gel and sometimes soap (with animal fat).
Variations in this formula are found from one end of the country to the
other.
The recipes are never the same and with quite amount of variance. The
use of it with earthen plasters is even less common, but probably the
most useful technical information comes from a study done in Peru
several years ago where they tested a variety of stabilizers with
earthen plasters. These included asphalt, banana, prickley pear,
locust beam tree. The prickley pear was soaked in water using equal
proportions of weight for both cactus and water. Wall sections were
tested using a simulated rain cycle via hydraulic methods. Walls were
subjected to 20 cycles of 3 hour long rains.
In short, after nine cycles, the control section of wall that had no
stabilizer had eroded 613 grams of material after only 9 cycles of
simulated rain while the test wall with pp gel eroded only 28 grams of
material after 20 cycles. In contrast, test walls with 2% and 4%
asphalt eroded 60 grams (2%) and 15 grams (4%) in 20 cycles. In our own
personal experience, we would say that it has a certain degree of
effectiveness, certainly better than unstabilized earthen plastered
walls.
Sunny John Cruikshank also has a small building with pp stabilized
earthen walls that has shown good results. However, we have gotten
better results from mixtures using casein and linseed oils. We have
found mixing times also to be a major variable in the process of
producing a good plaster.
In short, I would say that acceptable results, as good, if not better
could be achieved by using other materials and that its preferred use
over time has been primarily with lime. Shallow porches or something
that approached a cross between a porch and a generous overhang might
also lessen the demands made on the need for a stabilizer.
Bill
++ this info provided as part of my 10th Anniversary Celebration -share
it!!
Charmaine Taylor Publishing
10th Year $10. book Sale on 100+ books/dvds
www.dirtcheapbuilder.com
Order toll free 1-888-441-1632 12-4PST
PO Box 375 Cutten CA 95534
