Abstract

This project was a test of natural plasters, finished with a protective lime-wash coat of natural paint, for outdoor application. The client was Campus Center for Appropriate Technology (CCAT), who was expected to fund the materials, as well as provide the test surface of a wood frame wall. The wall was constructed of two different 4' by 4' natural surfaces: one in-filled with paper-crete bricks mortared together with paper-crete slurry, and one stick framed with wood lath and holding infill of cob (also known as wattle & daub). Both sections were constructed by Myles Danforth as his class project and were in the test phase. Following research, work on the plastering and finishing half of the project took place in three phases. 1. Test a variety of natural plaster and pigment formulations. 2. Based on the plaster results from Phase 1, select and apply two plasters for each section of the test wall, resulting in four final test sections. 3. Based on the pigment results from Phase 1, paint the plastered surface with a natural paint to match to the nearby official HSU signage columns. In preparation for this project, I took workshops in Natural Plastering and Painting under Penelyse Goodshield of Sustainable Nations[Sustainable Nations], and conducted book and online research. I conducted this project over the summer of 2009. With the exception of some assistance from classmates, the labor input was all my own. I would not endorse approaching such a project alone, as it was a very labor intensive. The finished product, however, achieved the goals set forth.

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Introduction

I took up the second part of the experiment; I researched and tested different appropriate-tech plasters with which I finished Myles' wall. After research and testing of a number of plaster formulas, I settled on two to apply to the wall so that weathering and stability could be compared over time. A clay-slip is usually applied as a binder between the wall itself and later plaster[1]; thus, the application of a clay-slip was my first step in actual construction. As we jumped through the bureaucratic hoops of campus building codes, we learned from the Building and Maintenance department that any permanent structure we built (including the experimental wall) needed to match the approved campus color scheme; as a result, part of the definition of 'appropriate' for my end of the project was to get the color right, which was purely a bureaucratic necessity but a necessity nonetheless. As it soon came to my attention that natural pigments stretched much farther in paints than in plasters, devising an appropriate natural paint was added to my to-do list; it is much more appropriate from a financial standpoint and a resource conservation standpoint to use less pigment, (usually mined minerals). In tune with CCAT's educational mission, Myles requested that a window be built into the plaster so that the paper-crete and wattle & daub would remain visible to future students and builders. My end of the project was thus broken into multiple tasks: 1. Materials research 2. Materials acquisition 3. Experimentation with plaster recipes 4. Experimentation with paint pigments 5. Designing (with Myles' advisement) and installing the window section 6. Applying the clay slip 7. Applying four strips of experimental plaster (one strip of each of my two final plasters over each of Myles' two wall materials) 8. Applying lime-wash color coat. 9.Curing the lime. I considered trying different paints as well, but this seemed to put too many layers of variables into the experiment. Instead, I decided on a single paint formulation during the research phase; the only experiment in the paint coat was how well I could match the school column color as per the Building and Maintenance department requirement.


A shot of the wall as Myles left it; before I started. Paper-crete is on the left in gray and the Wattle & Daub the earthen colored section to the right. The rest of the structure includes gravel bed, brick foundation, timber framing and tile roof.


Project Requirements

As opposed to mainstream construction and technological applications that are more often of a one-size-fits-all approach, the Appropriate Technology approach requires carefully thinking through your goals to find a best balance for the given circumstance. The immediate goal of this project was to design and apply materials that the good folks at CCAT would observe over the course of the following year; the long term objective being to build an entire structure using the best materials as determined by the results from this experimental wall. Since the project is for CCAT, features of Appropriate Technologies like LOCAL, NATURAL, or RECYCLED MATERIALS, COST-EFFECTIVENESS, REPEATABILITY BY NON-EXPERT BUILDERS, and WORK DURATION, were important. However, because the intention is to eventually make permanent structure(s) based on this experiment, I ranked DURABILITY (tempered by these others) as the biggest priority. Since the HSU Building and Maintenance department requires permanent structures to match approved color schemes, this bureaucratic requirement of MATCHING THE APPROVED COLOR SCHEME was also central in determining the success of this project. Finally, as a painter by trade, I consider AESTHETICS to have a high value for structures of all types.

Design

Materials

The first task was materials preparation. Research informed me that traditional technologies for water-resistant earthen plasters are lime (the mineral) and manure [2]; another choice might have been using a natural oil such as linseed oil as an additive (here termed amendment) [3], but oils block water more completely, whereas Myles' wall materials of paper-crete and wattle & daub are often used for their vapor-permeability (Danforth, 2009). Vapor-permeable surfaces are considered advantageous in natural building because they allow interior and exterior humidity levels to attain equilibrium by first absorbing in, then wicking away excess moisture, not allowing it to build up within [4]. Using an oil amended plaster would eliminate this vapor-permeable quality of the wall materials, so it made sense to use the vapor-permeable, yet humidity durable, lime and manure plasters. I found a variety of formulas for mixing plaster using these key ingredients. Additional ingredients included builders’ sand, lime-putty, manure, straw, clay and wheat- paste. A brief discussion of each: qualities, how I prepared them for use, where I got them, etc., follows.

Builders Sand

Sand is a component of most plasters; on a molecular level it is crystalline in structure and interlocks like a 3-D jigsaw puzzle, providing mechanical strength [5]. I could have used beach sand for this, but mixed grade builders sand is best because it has different size crystals to interlock; more uniform sized sand particles like I would find at a beach would create weaker bonds[6]. This might be okay for other projects, but as durability is one of my chief criteria, I wanted to use the most durable ingredients. Another problem with beach sand would be the difficulty of washing it, as natural salts would represent an unquantifiable (for my purposes) variable, possibly reacting in my plaster recipes. Factory sand represents a higher embedded energy cost, but allowed me to test these formulas at their strongest potential quality levels without an odd variable throwing off the results. A practical, non-experimental design might well opt for the lower embedded energy and financial cost, and added labor cost of washing local sand. My mixed grade builders sand was donated from ripped, so un-saleable, bags available at the local hardware store.

Lime Putty

Lime is a basic ingredient in earthen cements because it adds a binding quality to the mix; it is also known for high durability under adverse weather conditions [7]. Lime is available at hardware stores in the form of a powder. I used Type S Hydrated Lime. It is important to use builders lime and not agricultural lime; there are a variety of lime powders so be sure you know which one you get, as they all require different handling [8]. Lime is caustic and will burn, vinegar is recommended to be kept on hand as a chemical counter-agent for first-aid [9]. (Even with gloves and rubber coveralls I managed several chemical burns over the course of the project, thanks be to vinegar.) Lime Putty is produced by slaking (soaking) lime in water. For Type S Hydrated Lime it can be used within 1/2 hour of mixing, but all lime putties improve in quality with increased slaking time [10]. I was lucky enough to be able to slake my lime for a period of several months; I acquired it early in my spring semester and didn't start construction until the summer months. Keep in mind that the lime that went into the finished wall had slaked for several weeks longer than the test batch, so was that much improved. [Recipe under Appendix II: Important Recipes.] Lime is processed by being burned in kilns, which releases CO2 into the atmosphere. However, as lime plasters, washes, etc., dry and begin curing, they react with moisture in the air, eventually pulling the same amount of CO2 back out of the air released during burning and turning back into limestone around the other mix ingredients; so not counting transport, packaging, etc., the lime itself is carbon neutral though cyclically adding and removing CO2 to and from the atmosphere [11]. My Type S Hydrated Lime was donated from ripped, so un-saleable, bags available at the local hardware store

Manure

Manure is a traditional building material in many parts of the world, it mixes well with earthen ingredients, retaining vapor-permeability, while containing natural enzymes which make it water-resistant, and also natural (undigested) fibers (see section on Straw for discussion of Tensile strength), (Guelberth, Rose & Chiras, 2003). I opted for horse manure as there was a stable up the road which was happy to have me reduce their manure pile. My manure was therefor not fresh. So this too I placed in a 35 gallon container and added water to to bring it back to a softer more workable state. However, because it had been sitting around for some time there were issues with both mold and bugs. Gross as it sounds, to account for this I first carefully picked through the manure selecting only the least bug and mold ridden parts to keep. A previous class (Engineering 114) had revealed that the household natural cleanser Borax is used in earthen building as a mold inhibitor. I also knew of its' usefulness in killing bugs as I'm told it works its' way into their joints destroying them. This might sound cruel to animal lovers but a bug infested wall was not an option. I did not find clear indications of how much to use however, so I guess-timated adding about a half-cup of Borax powder over about each foot of depth of manure in my bin. This seemed adequate for squelching the mold but the bugs would return so I'd mix in more in an add-hoc manner over the weeks as I went. Certainly the Borax was but a small percentage of my manure, but I can not account for it by weight, volume or any other measure of how much went in, so the more scientific minded should be aware of this 'loose' variable in my formulas.  (Some formulas contain it explicitly and are noted by volume)

Straw

Straw is used in earthen building to provide Tensile strength (Engineering 305); think of it as akin to metal rebar in mainstream building. Straw allows the surfaces to bend and flex without coming apart, it also can be thought of as a material that spreads stresses as opposed to letting stress fracture off a given section of plaster. Research said that straw should be between 1-3 inches in length for a plaster, well dried with no mold, (Guelberth, Rose & Chiras, 2003). One method that was recommended for me to cut the straw to the right length was to put it in a trash bin and weed-wack it. I couldn't find anybody to loan me their Weed-Wacker to try it though, and can't blame them, for advice or not such an approach sounds like an abuse-of-power-tools (probably would not be 'appropriate use of tech.' to destroy a power tool so as require its' replacement). Instead I got a wheel-barrel full at a time and cut it down with scissors using gloves as the stuff is tougher on the hands than you might guess. Cutting more straw became a welcome break during the project, I'd recommend not preparing it all at once to allow an easier task to change gears to as you work. Of course with more bodies it might not matter, working by myself it was a welcome relaxer though. Ms. Goodshield suggested that one inch straw is recommended for top coats of plaster, first (Key or Scratch) coats should have longer straw to give later coats material to grip to. Before I applied my finish coat of plaster I actually took scissors and trimmed the wall to ensure longer pieces would not stick out after the finish coat went on. I had straw bales on-hand at the site that I was welcomed to work from.

Clay

Clay, like sand and straw, is a basic component of bricks and plasters. Though I'm focusing in on lime and manure I wanted to try some more raw earthen mixes to see if they could compare durability-wise, if so such mixes would represent lower embedded energy costs than the lime for sure, than manure anywhere where ruminant animals are not common. In basic earthen plasters clay acts as the glue that holds the other elements together, (Guelberth, Rose & Chiras, 2003). Clay is available for sale through potters suppliers, etc, but can also be dug right out of the ground. However, high silt ratios in ground clay are bad for building. There are several easy tests to determine clay suitability, the easiest being to roll it between your fingers to make a clay 'worm'. If the worm holds its' shape then the silt content is low enough to make a decent building clay. A more precise, but still field test is available on Myles' page: http://www.appropedia.org/CCAT_natural_wall_construction. Here I cheated, when I brought my resident expert, Ms. Goodshield out to review my materials before I began, she waxed eloquently about how wonderful the quality of the clay was at the CCAT grounds where I was working and how she only wished she could get clay as good; that I was lucky to have it right there on-hand. So I trusted her. As another pair of students were building a retaining wall and so digging up a lot of clay in process, I helped them by getting it out of their way and into another trash-bin. This material I screened by hand through quarter inch screens stapled to wooden frames in order to remove rocks and other debris. From there all I needed to do was keep it hydrated so that it would not turn rock-hard on me but retain a putty-like consistency.

Wheat Paste

Wheat Paste is a basic natural glue. I needed it to make a clay slip (more later) so since I would be using it already, decided to add it to my plasters in different ratios to see if it was useful as an amendment. I figured the plasters made of lime would cement up well and hypothesized that wheat paste glue might help the rawer formulas to compete. Wheat Paste is easily made. Start with high gluten organic (to keep extraneous chemicals that might react with other ingredients out of the mix) wheat flour, do not use whole wheat as it is low gluten and the gluten is the gluey part. Get three quarts of water boiling in a six quart pot. In another container mix the flour with cold water stirring until lumps are gone and the consistency of pancake batter is reached. Slowly add cold mix to boiling water stirring carefully and maintaining a boil, ( if you lose the boil just cook longer). You are done when the mix becomes translucent, don't expect it to be completely see-through, close is just right. Your glue will keep in the fridge over-night, but fresher is better, don't use older than day old wheat paste. (Guelberth, Rose & Chiras, 2003). (Note: Useful to glue all sorts of things, like using to poster walls- 'going wheat-pasting'). I bought my organic wheat flower from the local co-op.

Formula

[Note: the section that follows details the experiments conducted and results analyzed in order to arrive at my final plaster and paint recipes. I do not believe this will be of interest to most builders. Skip down to the section titled Conversion of Final Decision Recipes To 1gal Ratios. Here are formulas to mix my best lime recipe, #2; my best manure plaster, #4.3; and my best earthen mix, #5.7. With these you can jump straight into building. Unfortunately, unless you opt for our school pinkish stucco, you will have to experiment with coloring your own lime-washes (paint), my simple trial-and-error process is therefor described under Getting the Color Right. For step-by-step construction instructions, as well as project synopsis, please continue to web page two, [[2]].]

Stress Test 1 Design Having researched some plaster formulas, and gathered and prepared my ingredients, it was time to make some test plasters and figure a way to administer stress tests. I devised two tests that I used in conjunction. The first test was to take a wire brush like used in construction, about an inch width of wire by five inches length mounted in about a foot long handle. My idea was to use a weight on the brush to scrub the plasters, letting the weight do the work of pushing down and trying to keep my muscle just maintaining a back and forth motion. The amount of weight wasn't in my mind important, just that it remain more or less constant. I taped a fist sized rock from the yard onto the back of the brush for weight, then after a few practice runs decided that thirty strokes front and back was an appropriate amount to damage the plasters while leaving enough behind to compare. I used strokes as long as I could across my test patches that averaged about six inches square.

Stress Test 2 Design The second test was a water test. I decided to shoot my garden hose full blast, for my pipes not a lot of pressure actually, at the plasters where they were undamaged by the brush test. Again, the amount of water pressure wasn't deemed important for my purposes, just that it was uniform, so full blast it was. To contain the flow, or keep it aimed in full pressure against the plaster, I cut a garden hose size opening into a plastic single-serving yogurt cup like you'd get in any chain super market, then cut about a two inch slit in the edge that would touch the plaster to allow some pressure to escape out and away in a direction I would determine. This ad-hoc funnel I taped more or less water tight onto the end of the hose with duct tape. The idea was both for the blast to be concentrated where I aimed, but not allow an unquantifiable pressure build-up to be doing the work; I also thought that to allow moisture to escape outside the cone radius, weakening surrounding areas to a lesser extent, gave me a second test surface to note damage, all from the one test. Using a watch with a seconds hand I decided, after a little trial and error, that two five second blasts at the same spot, ten seconds apart, provided the just right amount of damage from which to make comparisons.

Finally, I allowed the water test to dry out over night, under heat lights and fans. Now I repeated the water test, only this time blasting about a third of the way up into brush strokes creating areas in the brush line that got full-blasted by water, others just moistened by proximity, and others not wet at all on the far end; these to compare against the first water test on undamaged plaster, and areas not abused at all except through proximity to the other tests.

All the plasters had been allowed to dry for about a week onto particle board that had been prepared with a clay slip as an adhesion coat, what in normal house painting I'd call a primer. So here I include the recipe for Clay Slip, (thanks to Ms. Goodshield).

There are many ways to mix natural plasters.

[Recipe for Clay Slip (Adhesion Coat): Starting with previously screened clay, mix with water until thickness of heavy-cream is achieved, mix in 1/2 cup wheat paste to five gallons slip, I erred a tablespoon or so heavy here. Slip paints on and can even be sprayed with the proper tools, I used a cheap 3 inch brush.]

Mixing clay slip with a drill attachment; my drill motor gave out due to the high torque involved so i did most of my mixing literally by hand, squeezing and kneading.

I applied these tests (brush, hose, hose on brush mark) twice before I selected the plasters I would use. The first round was a 'discovery' round in which I used five basic plaster mixes. Then learning what I could, I made 26 variations of my best recipes from the 'discovery' round. Out of this 'decision' round of 26 plasters tested, I selected the two best to try on the wall.

Discovery Test: Recipes, Results, & Conclusions

Discovery Recipes:

[When I use a Pinch as a measurement, I mean a two-finger and thumb dollop, probably about a heaping tablespoon. I describe straw amounts' roughly for the reason that straw doesn't fill out a volume like my other ingredients, does one pack it in the measuring cup or place it loose, unscientific as it is I opted for a loose packed somewhere between the extremes; by weight would have been more precise but I didn't feel like a job site was a good place for a precision scale.]

1. Light Lime Plaster: 1 cup lime putty, 2 cups sand, 1 pinch wheat paste, 1 pinch clay, add straw to 1/2 volume of mix, add water after straw to regain wet plaster consistency.

2. Lime Plaster: follow recipe 1 but add no wheat paste or clay.

3. Manure Plaster: 1 cup clay, 1 cup sand, 1 cup manure, 1 pinch wheat paste.

4. Light Manure Plaster: 1 cup clay, 1 cup sand, 1/2 cup manure, roughly 1/2 cup straw, 1 pinch wheat-paste.

5. Earth-Lime Plaster: 1 cup clay, 1 cup sand, 1 cup lime putty, roughly 1 cup straw.

'Discovery' Test Results

Hypothesis: I expect recipe # 2- Lime Plaster, to perform best, and # 5- Earth-Lime, worst.

Results After Brush Test: least damaged to worst- Lime*, Light Lime, Light Manure, Earth-Lime, Manure

Analysis:

-The Lime Plaster was barely damaged at all (too good?) inspiring a retest, *still undamaged after retest.

-The Light Lime beat all but the Lime Plaster itself.

-The Manure Plaster was cut through like butter, useless.

-The Earth-Lime almost tied for third place with the Light Manure, defying my hypothesis, food for thought.

Results After 1st Water Test (undamaged area): least damaged to worst- Lime, Light Lime, Light Manure & Earth-Lime tied, Manure

Analysis:

-Lime Plaster was clearly undamaged after both tests.

-Light Lime had moderate damage, mostly by brush not water.

-Light Manure's outer rim held up to brush & spray, center point of spray 100% damaged clear through.

-Earth-lime's outer rim damaged clear through by brush, center held up well to both.

-Light Manure vs Earth-Lime: Light Manure good to friction but horrible to water pressure, whereas Earth-Lime prone to friction damage on edges but good otherwise.

-Manure heavily damaged but mostly by brush, held up well to water, (demonstrating, I believe, the water-proofing qualities of the enzymes in the manure, when, compared to Light Manure, there is enough to get the effect).

Results After 2nd Water Test (aimed at brush damage): least damaged to worst- Lime, Light Lime, Earth-Lime, Light Manure, Manure

Analysis:

-Here the Earth-Lime clearly edged out either manure mix.

-Recipe #2, the heaviest lime mix came out the best per my hypothesis.

Overall Analysis:

Point 1- The lime made an excellent plaster, more the merrier.

Point 2- The fiber content of just manure doesn't seem enough for a stable plaster; the straw clearly made the difference in Light Manure over Manure Plaster, and showed strong anti-abrasive qualities in the brush test for plasters Light Lime, Light Manure, & Earth-Lime. Therefor I will make no more manure plasters with no straw added.

Point 3- The only recipe without wheat-paste was the best.

Revised Hypothesis:

H1- Per point 1, if I make a revised Earth-Lime recipe 5.1 without lime, it will fail.

H2- Per point 1, a revised Light Manure recipe with lime added might allow it to compete with the Earth-Lime, or even get it back into comparable range of the lime plasters.

H3- Per point 3, any recipe might improve with lime used instead of wheat-paste as a glue/cement.

'Decision' tests: Thoughts, Revised Recipes, Results, Analysis, Conclusion

Thoughts from Discovery Tests: The raw Lime Plaster, #2, clearly won, the decision round should try to find a manure or earth-lime plaster mix that will come close with lower embedded energy costs. The Lime Plaster should be altered in ratio to find a best mix. The Earth-Lime should be altered in ratio to find a best mix. Won't give up on manure, but add lime to variations of recipe 4, Light Manure Plaster, to attempt to find a mix that beats out the earth-lime mix. For the manure recipes, my gut tells me to throw in some borax as an anti-mold/fungal/insect amendment, but that this won't be necessary in the recipes with lime.

Revised Lime Plaster Recipes:

2. 3/4 cup lime putty, 2 1/4 cup sand, 1/2 volume straw, H2O to hydrate to wet plaster consistency; 2.1 (add clay, reduce lime) 1/2 cup lime putty, 1/4 cup clay, 2 1/4 cup sand, 1/2 volume straw, H2O to hydrate; 2.2 (add manure, reduce lime) 1/2 cup lime putty, 1/4 cup manure, 2 1/4 cup sand, 1/2 volume straw, H2O to hydrate; 2.3 (add wheat-paste) recipe 2, add 1/8 cup wheat-paste; 2.4 (increase straw) recipe 2 but instead of 1/2 straw by volume add 3/4 straw by volume; 2.5 (reduce straw) recipe 2 but instead of 1/2 straw by volume add only 1/4 straw by volume; 2.6 (increase sand) 3/4 cup lime putty, 2 1/2 cup sand, 1/2 volume straw, H2O to hydrate; 2.7 (reduce sand) 3/4 cup lime putty, 2 cup sand, 1/2 volume straw, H20 to hydrate; 2.8 (increase straw and sand, add wheat-paste) 3/4 cup lime putty, 2 1/2 cup sand, 1/8 cup wheat-paste, 3/4 volume straw, H20 to hydrate; 2.9 (reduce straw and sand) 3/4 cup lime putty, 2 cup sand, 1/4 volume straw, H20 to hydrate.

'Decision' Test Results for Lime Plasters

Results After Brush Test: Least Damaged to Worst- 2; 2.9; 2.5; 2.7; 2.8; 2.1 & 2.6 tied; 2.3 & 2.4 tied: 2.2.

Results After 1st Water Test: All undamaged (!), except 2.1 & 2.6 are barely damaged, 2.2 significantly damaged in corner that wasn't blasted, got wet though where a crack appeared when the plaster first dried out, this corner broke off.

Analysis: 2.2 was worst in both tests so will eliminate from second round of water tests, 2.1 and 2.6 also eliminated because tied at 3rd worst in brush test and 2nd worst in first water test.

Results After 2nd Water Test: 2 is still barely damaged at all, followed by 2.5 then 2.9 as close second and third.

Analysis: 2.5 and 2.9 both have more lime than 2 so represent a higher embedded energy cost, I would think not to use them, going for 2 the best overall, however, 2.9 was second place after the brush test, and it came out smoother on the surface so I might use this recipe as inspiration for a finish/top coat.

Revised Manure Plaster Recipes:

4. 3/4 cup clay, 3/4 cup sand, 3/8 cup manure, roughly 3/8 cup straw, 1 pinch wheat-paste, 1 pinch borax; 4.1 (add lime, remove borax) 3/8 cup clay, 1/4 cup manure, 3/8 cup lime putty, roughly 3/8 cup straw, 3/4 cup sand, 1 pinch wheat-paste; 4.2 (add lime, remove wheat-paste & borax) [checks hypothesis 3] follow recipe 4.1, but do not add wheat-paste; 4.3 (increase manure to clay, add lime, remove borax) 3/8 cup clay, 3/8 cup manure, 3/8 cup lime putty, roughly 3/8 cup straw, 3/4 cup sand, 1 pinch wheat-paste; 4.4 (increase sand & straw, add lime, remove borax) [this recipe adds dry material and is tested as a possible Scratch/Key (1st) coat] 3/8 cup clay, 1/4 cup manure, 3/8 cup lime putty, roughly 1/2 cup straw, 7/8 cup sand, 1 pinch wheat-paste; 4.5 (increase straw & manure, add lime, no borax) [adds 1/8 cup dry material, another possible Scratch coat] 3/8 cup clay, 3/8 cup manure, 3/8 cup lime putty, roughly 3/4 cup sand, 1 pinch wheat-paste; 4.6 (increase sand, straw & manure) 3/8 cup clay, 3/8 cup manure, 3/8 cup lime putty, 7/8 cup sand, roughly 1/2 cup straw, 1 pinch wheat-paste [another possible Scratch coat].

'Decision' Test Results for Manure Plasters

Results After Brush Test: Least Damaged to Worst- 4.5; 4.3; 4.4; 4.6; 4.1; 4.2; 4

Results After 1st Water Test: 4.1; 4,3; 4.4; 4.5 all undamaged by water, 4.6 slightly damaged followed closely by 4.2, 4 very damaged.

Analysis: 4 came out worse in both tests so it was easy to eliminate, because it contained no lime it well supports Hypothesis 2. 4.2 & 4.6 were the only others to show damage from the water, as well as fall below the bottom half on the brush test so these too were eliminated from round 2 of the water test.

Results After 2nd Water Test: 4.5 was badly damaged so is easily eliminated, 4.4, 4.5, & 4.6 showed minor damage whereas 4.3 remained the only undamaged manure plaster and with its' second place in the brush tests shows itself to be the best overall manure plaster.

Analysis: The possible scratch coats did not perform well enough to warrant use.

Revised Earth-lime Plaster Recipes:

5. 3/4 cup clay, 3/4 cup sand, 3/4 cup lime putty, roughly 3/4 cup straw, 1 pinch wheat-paste; 5* (no lime to check hypothesis 1) 1 cup clay, 3/4 cup sand, roughly 3/4 cup straw, 1/2 cup wheat-paste, 1/8 cup borax; 5.1 (no wheat-paste, check hypothesis 3) follow recipe 5 but add no wheat-paste; 5.2 (increase clay to lime ratio) 7/8 cup clay, 3/4 cup sand, 5/8 cup lime putty, roughly 3/4 cup straw, 1 pinch wheat-paste;5.3 (increase lime to clay ratio) 5/8 cup clay, 3/4 cup sand, 7/8 cup lime putty, roughly 3/4 cup straw, 1 pinch wheat-paste; 5.4 (clay-manure instead of clay) 3/8 cup clay, 3/8 cup manure, 3/4 cup lime putty, 3/4 cup sand, roughly 3/4 cup straw, 1 pinch wheat-paste; 5.5 (clay, manure & lime in even proportions) 1/2 cup clay, 1/2 cup manure, 1/2 cup lime putty, 3/4 cup sand, roughly 3/4 cup straw, 1 pinch wheat-paste; 5.6 (increase straw) 3/4 cup clay, 3/4 cup sand, 3/4 cup lime putty, roughly 1 cup straw, 1 pinch wheat-paste; 5.7 (increase sand) 3/4 cup clay, 3/4 cup lime putty, 1 1/4 cup sand, roughly 3/4 cup straw, 1 pinch wheat-paste.

'Decision' Test Results for Earthlime Plasters

Results After Brush Test: Least Damaged to Worst- 5.7; 5.1; 5.2; 5 & 5.4 tied; 5.6; 5.8; 5.3; 5.5; 5*

Analysis: 5* broke apart completely so strongly supports hypothesis 1; 5.1 in second place lends credible support to hypothesis 3.

Results After 1st Water Test: 5* is significantly damaged, 5.2 & 5.8 show slight damage, all others undamaged.

Analysis: 5* is worse on both tests so hypothesis 1 is still strongly supported and 5* will be eliminated from the 2nd round. 5.8 also warrants elimination as it tied for 2nd worst on the water test and came in the bottom third with the brush. 5.1 is doing well, still supporting hypothesis 3.

Results After 2nd Water Test: All remain fairly undamaged.

Analysis: 5.7, as clear winner in the brush test wins this tight round.

Overall 'Decision' Test Results:

Mix # 2, the rawest lime recipe came out best overall. 4.3 and 5.7 took their respective categories but are too close in final appearance to call a winner. Further testing was warranted so I tried at first just scratching the still wet surfaces with my fingernail- inconclusive. So I decided to try the wire brush again over the now wet previous brush marks, after 10 strokes no difference, after 15 4.3 went all the way through, after 19 5.7 went through, after 20 strokes 4.3 looked worse than 5.7. So my decision came down to 5.7 being best in the tests, but 4.3 using only half as much lime for a much lower embedded energy cost. I chose 4.3 for the wall, I felt the difference was slight enough that I could trade durability, my top criteria, for lower embedded energy. I figured my tests, while relevant and revealing, were not after all really what Arcata weather would throw at the wall, and there was a chance that things would come out very differently under real conditions; this thought justified to me making a go with the lower energy alternative: the 4.3 manure mix.


Getting the Color Right:

Part of the requirements for this project was to match the wall color to the school stucco color, a beigish pink.  This I probably had the least success with, though as close as I got it really wasn't bad at all.  To start it is necessary to first make a lime-wash.  This is done by mixing 2 parts lime putty to 1 1/2 parts water.  Mix this well, it should be about as thick as whole milk.  Pigments must be first added to water, then mixed into the lime-wash.  Be sure to mix the pigment fully into the water to avoid clumping of pigment in the wash, (HSU Ceramics dept.).  After all are mixed it is wise to run all through a strainer like available through a paint store, I found that cheesecloth worked well enough.  


My first run through I missed the pink tone and used combinations of yellow iron oxide, yellow ochre, and burnt umber mineral pigments mixed in quantities of 1/8 cup with 1-4 cups lime-wash.  This created various beige tones, that when allowed to dry and compared against nearby columns revealed my need to move in a pink direction.  That failed first batch consisted of eleven different samples.  However, I did learn enough to try more precise ratios the next go, my mixes at one cup lime-wash were obviously too dark.

The pigments are powdered minerals, mix them completely into water before adding to paint recipes to avoid ugly color clumping.


The second batch consisted of 15 samples- 3 came close.  The first of the three consisted of 3 cups lime-wash, 1/8 cup yellow iron oxide and 1/8 cup red iron oxide.  This recipe was a little too dark.  The next two were very close in tone and I could have opted for either.  Mix two was 2 cups lime-wash, 1/8 cup yellow iron oxide, and 1 tablespoon red iron oxide.  The third mix was 2 cups lime-wash, 1/8 cup yellow ochre and 1 tablespoon red iron oxide.  I chose this last mix because yellow ochre was cheaper than yellow iron oxide.  Converted to gallon ratio the color mix I settled on was 1 gallon lime-wash, 1 cup yellow ochre, 1/2 cup red iron oxide.


During my test phase I was advised and given pigments by the professors of the campus ceramics lab, to whom I offer my gratitude.   When I actually readied to make my lime-wash for the color coat, I bought pigment from the local ceramics supplier.


Conversion of Final Decision Recipes to 1 gallon ratios

Recipe for plaster # 2, the Lime Plaster finalist@ 1 gal:

3/4 cup lime putty x 16 cups (1 gal) = 48/4 = 12 cups lime putty


2 1/4 cups sand = 9/4 cups x 16 = 144/4 = 36 cups sand


1/2 volume straw


H2O to hydrate to plaster consistency


Recipe for plaster # 4.3, the Manure Plaster finalist@ 1 gal:

3/8 cup clay x 16 = 48/8 = 6 cups clay


3/8 cup manure becomes 6 cups manure


3/8 cup lime putty becomes 6 cups lime-putty


3/8 cups straw becomes 6 cups straw


3/4 cup sand x 16 = 48/4 = 12 cups sand


1/8 cup wheat-paste x 16 = 16/8 = 2 cups wheat paste


H2O to hydrate to plaster consistency


....and finally the plaster I will not use, but tested well so you might, recipe for plaster 5.7, the Earth-Lime finalist@ 1 gal:  

3/4 cup clay becomes 12 cups clay


3/4 cup lime putty becomes 12 cups lime-putty


1 1/4 cups sand = 5/4 cups x 16 = 80/4 = 20 cups sand


3/4 cup straw becomes 12 cups straw


1/8 cup wheat-paste becomes 2 cups wheat-paste


H20 to hydrate to plaster consistency


References

Thanks to Pennelys Goodshield of Sustainable Nations for invaluable training and advice, as well as to, Myles Danforth and Lonny Grafman.

  1. Goodshield, P. (2009). Workshop Director, Sustainable Nations, (http://sustainablenations.org/). (K. S. Perry, Interviewer) Arcata, CA. First I took I work-shop with Ms. Goodshield on natural plaster and lime-wash. Then I was able to interview her several times and she stopped by the site to consult once.
  2. Guelberth, Cedar Rose & Dan Chiras. The Natural Plaster Book: Earthen, Lime, and Gypsum Plasters for Natural Homes. Gabriola Island, BC, Canada: New Society Publishers, 2003.Of all the books I read through, only one did I find myself drawn back to over and again.... This book seemed to have, compared to others, the most agreed upon and middle-of-the-road recipes; I derived all my basic formulas from it and barely scratched the surface.
  3. Guelberth, Cedar Rose & Dan Chiras. The Natural Plaster Book: Earthen, Lime, and Gypsum Plasters for Natural Homes. Gabriola Island, BC, Canada: New Society Publishers, 2003.
  4. Guelberth, Cedar Rose & Dan Chiras. The Natural Plaster Book: Earthen, Lime, and Gypsum Plasters for Natural Homes. Gabriola Island, BC, Canada: New Society Publishers, 2003.
  5. Graffman, Lonny. (2009, Spring Semester). Engineering 305. Humboldt State University, Arcata, CA. This class provided much useful basic information for this project.
  6. Danforth, Myles. (2009, Spring). (K. Scott Perry,Interviewer) Arcata, CA. Myles was knowledgeable and had plenty of helpful advice.
  7. Guelberth, Cedar Rose & Dan Chiras. The Natural Plaster Book: Earthen, Lime, and Gypsum Plasters for Natural Homes. Gabriola Island, BC, Canada: New Society Publishers, 2003.
  8. Guelberth, Cedar Rose & Dan Chiras. The Natural Plaster Book: Earthen, Lime, and Gypsum Plasters for Natural Homes. Gabriola Island, BC, Canada: New Society Publishers, 2003.
  9. Mallinckrodt Baker, Inc. (2009, September 23). Material Safety Data Sheet, Calcium Oxide. (Environmental Health & Safety, Producer) Retrieved December 19, 2010, from [[1]]. Technical specifications of lime from a chemical / industrial standpoint.
  10. Guelberth, Cedar Rose & Dan Chiras. The Natural Plaster Book: Earthen, Lime, and Gypsum Plasters for Natural Homes. Gabriola Island, BC, Canada: New Society Publishers, 2003.
  11. Lyons, Arthur. (2007). Materials for Architects and Builders (3rd ed.). San Diego, CA, USA: Butterworth Heineman. A University text designed for professional builders. Notable for its' background on lime, and chemistry equations for those interested.



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