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CCAT Exterior Natural Wall Plaster & Paint, Part1

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This project is a test of natural plasters for outdoor application; to be finished with a protective and coloring coat of natural paint. The client is CCAT (Campus Center for Appropriate Technology), at Humboldt State University, Arcata CA; initiated by my participation in the class Engineering 305 which requires an appropriate technology semester project. CCAT is expected to fund the materials as well as the test surface; a smallish wood frame wall which is being prepared with two different natural wall surfaces: paper-crete bricks and wattle & daub respectively, also both in test phase and constructed by Myles Danforth as his class project. Following research, work will take place in roughly three phases; (1) test a variety of natural plaster and pigment formulations in order to then (2), select two plasters for application onto the test wall, each of the two plasters to be applied to each of the two experimental surfaces, for four final test strips. Then finally (3) will be the painting of the now plastered surface with a natural paint which I'll have attempted to match to the nearby HSU official signage columns. I'm taking workshops in Natural Plastering and then Painting under Peneliese Goodshield of the organization Sustainable Nations as preparation, as well as doing book and internet research. I had planned to do the project during the spring semester, but between Myles needing to build the wall, followed by a long rainy season that led into finals, the project became a summer one. I had hoped to use volunteer/workshop labor but having outsiders on CCAT grounds over summer months conflicted with CCAT policy as described me by the interns. Therefor, aside from some hours put in by classmates at semester end, I performed all the labor myself, which I would not endorse as it was a very manually intensive project eating up about a month and a half. Be that as it may, the finished product seemed to achieve the goals we had set forth, details follow bellow.


I took Engineering 305: Appropriate Technology as the last class needed to earn a Minor in Appropriate Technology, or as I like to joke, my appropriate tech. merit badge. The class requires an intensive project that is to include not only research and hands on elements, but also the building of this Appropedia page. Projects can be entirely self-designed, or generated through a list of projects requested by various parties such as the Campus Center for Appropriate Technology- CCAT. I'd had thoughts of attempting to refine previous projects by attempting to 'assembly line' them to increase efficiency and practicality. However, in discussion with Professor Graffman and some student colleagues, (notably, Miles Danforth, over whose work I would add finish elements, and whom would prove knowledgeable and extremely supportive and helpful throughout), we decided I should draw upon my decade worth of experience as a painting contractor (interior/exterior, commercial residential) and take on a CCAT requested project to finish a wall with natural plasters and paints which I was to design by way of an experiment to determine if such earthen-style construction would prove applicable to the moist Pacific Northwest environs of Arcata California. We agreed this project would be a good fit because as a painting contractor I would be more knowledgeable in the finishing tools and techniques known to mainstream contractors than most of my student colleagues, and hopefully I might be able to go on and use what I learned in this project in a professional capacity outside of school. I've long had an interest in natural paints, if not necessarily plasters, and this was the perfect opportunity to learn the ropes. Moreover I know I've a good 'touch' for such things and thought I'd be able to complete the project to high aesthetic standards regardless of how the materials experiment turned out.

Which leads my thoughts to the idea of what an appropriate technology is and is not. I don't mean this statement as any type of definitive, holistic discussion of the issue; but when I weighed the idea of designing my own project vs. going with the CCAT work-order, it seemed that a project for the sake of an assignment could not be deemed as appropriate as one addressing a need. CCAT intended to build in the next year or two, a new building on their grounds which they hoped to construct using natural or earthen materials. The question was what if any such materials were suited to their site: just on the edge of the redwood rain-forest the location is often shady in a town which is near the ocean, even closer to a bay, and known for its' wet overcast conditions, and regular ocean fogs. In my research into natural building one piece of advice I came across again and again was to look to the traditional methods of native (aboriginal) populations as a good starting place. The local amer-indians, (split into several tribal groups and still plentiful in the region,) seemed to favor the abundant forest products as building materials; so there seemed to be a legitimate question as to whether earthen building was at all suited to this dank environment. Since the work was going to lead up to a real and needed building project, it seemed like the most appropriate use of time, material, and energy.

To this end CCAT requested an experiment be done, in two parts, in order to determine appropriateness of such building technologies for such Pacific Northwest environs, in particular their own grounds. The first part was to research and experiment with different 'appropriate' materials to actually build an experimental wall with; asking that two materials be used in the finished wall to provide an experiment in comparing long-term weathering and stability. This first experimental work-order was taken up and completed by Miles Danforth. After determining that, a traditional foundation and wooden frame would work best for the site, Miles took on the job of building the wall itself. Miles' own Appropedia page details his process, but I'll say here that he settled for his two final experimental materials/construction technologies on a wattle & daub section, and a paper-crete brick section.

The second, and my part of the experimental work-order, was to research and experiment with different appropriate-tech plasters over which to finish Miles' wall; again settling with two different materials to actually apply to the wall so that weathering and stability could be compared over time. I learned early in my research that a clay-slip is usually applied as a binder between the wall itself and later plaster so the application of such would be 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 (which this was to be), needed to match the approved campus color scheme; so part of the definition of 'appropriate' for my end of the project was to get the color right- purely a bureaucratic necessity but a necessity none-the-less. 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 being much more appropriate from a financial standpoint and a resource conservation standpoint to use less pigment in getting the color matched. In tune with CCAT's educational mission, Miles requested that a window be built into the plaster so that the wattle & daub, and paper-crete would remain visible to future students and builders. So my end of the project would be broken into multiple tasks: materials research, experimentation with plaster recipes, experimentation with paint pigments, designing (with Miles' advisement) the window section, then applying the clay slip, applying four strips of experimental plaster- a strip of my two plaster finalists over each of Miles' two wall materials, and making sure the window was worked in. I considered trying different paints as well, but this seemed to put one layer too many of variables into the experiment; so I decided on a single paint formulation without undue experiment during the research phase; the only experiment in the paint coat being how well I could match the school column color as per the Building and Maintenance department requirement.

Project Requirements[edit]

The goal is to design and apply materials that the good folks at CCAT can observe over the course of the following year, so that in the long term they can build an entire structure using the best materials as determined by what holds-up on this 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, will all be important. However, because the intention is to eventually make permanent structure[s] based on this experiment, I'd have to rank DURABILITY as the highest goal to be achieved (tempered by these others). Moreover, as stated, the HSU Building and Maintenance department requires permanent structures to match approved color schemes, so this bureaucratic requirement of MATCHING THE APPROVED COLOR SCHEME will also of necessity be central in deeming the project successful or not. Finally, as a painter by trade I see AESTHETICS as having a high value for structures of all types; so this too will be a consideration.



First on the list of tasks was materials preparation. Research told me that traditional technologies for earthen plasters that are water-resistant are lime (the mineral) and manure; another choice might have been using a natural oil such as linseed oil but oils block water completely whereas Miles' wall materials (paper-crete & wattle & daub) are often used for their vapor-permiability. Vapor-permiable surfaces are considered advantageous in natural building because they allow interior and exterior humidity levels to attain an equilibrium, as opposed to conventional building which exerts great effortin its' war with the elements, so to speak. Using an oil would eliminate this vapor-permiable quality of the wall materials so it made sense to go with the lime and manure plasters which are themselves vapor-permiable while retaining a high factor of durability in wet conditions. I found a variety of differently ratioed formulas for mixing plaster using these key ingredients. Materials I'd need by way of ingredients included Builders Sand, Lime Putty, Manure, Straw, Clay and Wheat Paste. I'll discuss each briefly.

Builders Sand[edit]

Sand is a component of most plasters, on a molecular level it is crystalline in structure and so interlocks like a 3-d jigsaw puzzle providing Mechanical strength. I could have used beach sand for this but research told me that mixed grade builders sand is best so as to provide different size crystals to interlock; more uniform sized sand particles like I would find at a given beach would create weaker bonds. This might be OK on a given project, but as Durability is one of my chief criteria I wanted to test using the most durable ingredients. Another problem with beach sand would be the difficulty of washing it as natural salts would interact adversely with the plasters; these salts would represent an unquantifiable (for my purposes) variable which was a second good reason to go with factory prepared sands. This represents a higher embedded energy cost true, but again 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 and added labor cost of washing local sand. My mixed grade builders sand was donated from ripped so unsaleable bags available at the local hardware store.

Lime Putty[edit]

Lime is a basic ingredient in earthen cements and as such adds a binding quality to the mix, as well as being know for high durability under adverse weather conditions. Lime comes from hardware stores in the form of a powder- in my case Type S Hydrated Lime. It is important to ensure one acquires builders lime and not agricultural lime; also there are a variety of lime powders so be sure you know which one you get as they all require different handling. BEWARE- LIME IN ALL FORMS IS CAUSTIC AND WILL BURN YOU; DO NOT GET POWDER IN EYES OR INHALE! AVOID SKIN CONTACT AND KEEP VINEGAR ON HAND AS A CHEMICAL COUNTER-AGENT TO TREAT SKIN BURNS (even given gloves and rubber cover-alls I managed several chemical burns over the course of the project, thanks be to vinegar). Lime Putty is produced by slaking (soaking) lime, in whatever form, 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 (Roman law used to require a two-year slaking time for lime products produced in the empire). I was lucky enough to be able to slake my lime for a period of several months as 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. To slake the lime it is necessary to have a large heat and chemical resistant, clean container, I used a 35 gallon metal trash bin that I bought new. Unless using high-magnesium quicklime it is important to add water first then slowly add the lime powder. You will note a rise in temperature and a chemical boiling as the ingredients begin to interact. I wore my chem-resistant cover-alls, gloves, a respirator and goggles during this process. Be sure to stir well so no clumps of lime powder remain untouched and so unreacting to the water. Eventually (follow directions according to lime-type) the mixture attains a putty-like consistency about like a thin oatmeal. When well mixed make sure to leave a few inches of water on top to keep it from dehydrating then leave to slake for as long as you can. A Note About Lime- Lime is refined in kilns by means of firing, during this phase carbon is released into the atmosphere. However, once made into a plaster, mortar, brick or what-have-you, the material will cure over time, by the time it has cured completely it will pull the same amount of carbon out of the air that it released during firing, making it in the end a carbon-neutral material (not counting transportation, etc.)


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). 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. Research 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 guestimated 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 minute 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 is used in earthen building to provide Tensile strength; 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. I wondered if it would decompose over time, and discovered, akin to petrification, it actually calcifies in such mixes and so becomes more, not less durable with time. 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. 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, like sand and straw, is a basic component of bricks and plasters going back thousands of years. 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. 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. Here I cheated, when I brought my resident expert, Pennelyse Goodshield of Sustainable Nations 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[edit]

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 additive (sometimes called 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. 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. (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.


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.

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 thouch the plaster to allow some pressure to escape in a direction I would determine, out & away. 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 also allow moisture to escape outside the cone radius weakening surrounding areas to a lesser extent. 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.

[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]

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.... 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 wheatpaste.... 5. earthen lime plaster: 1 cup clay, 1 cup sand, 1 cup lime putty, roughly 1 cup straw....

'Discovery' Test Results.... Hypothesis: expect recipe # 2 to perform best and # 5 worst.... After Brush Test: least damaged to worst- 2*, 1, 4, 5, 3.... Analysis: 2- was barely damaged at all (too good?) inspiring a retest, still undamaged after retest.... 3- was cut through like butter, useless.... 5- almost tied for third place with 4, defying my hypothesis, food for thought.... After 1st Water Test (undamaged area): least damaged to worst- 2, 1, 4&5 tied, 3.... Analysis: 2- clearly undamaged after both tests.... 1- moderate damage mostly by brush not water.... 4- outer rim held up to brush & spray, center point of spray 100% damaged clear through.... 5- outer rim damaged clear through by brush, center held up well to both.... 4 vs 5- four good to friction but horrible to water pressure whereas five prone to friction damage on edges but good otherwise.... 3- heavily damaged but mostly by brush, held up well to water.... After 2nd Water Test (aimed at brush damage): least damaged to most- 2, 1, 5, 4, 3.... Analysis: here recipe 5, the earthen lime, clearly edged out either manure mix, but 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.... point 3- the straw clearly made the difference in 4 over 3, and showed strong anti-abrasive qualities in the brush test for 1, 4, & 5.... point 4- the only recipe without wheatpaste was the best....

Revised Hypothesis: H1- per point 1, if I make a revised recipe 5.1 without lime it will fail.... H2- per point 1, a revised recipe 4 with lime added might allow it to compete with the earth-lime mix #5.... H3- per point 4, any recipe might improve with lime used instead of wheatpaste....

'Decision' tests: Thoughts, Revised Recipes, Results, Analysis, Conclusion.... Thoughts form 'discovery' tests: The raw lime plaster clearly won, the decision round should try to find a manure or earthen plaster that will come close with lower embedded energy costs. The lime should be altered in ratio to find a best mix. The earthlime should be altered in ratio to find a best mix. Won't give up on manure, but add lime to variations of recipe 4 to attempt to find a mix that beats out the earthlime 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. 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 in 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.

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 wheatpaste) recipe 2, add 1/8 cup wheatpaste.... 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 wheatpaste) 3/4 cup lime putty, 2 1/2 cup sand, 1/8 cup wheatpaste, 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.... After Brush Test, Best to Worst: 2; 2.9; 2.5; 2.7; 2.8; 2.1 & 2.6 tied; 2.3 & 2.4 tied: 2.2.... 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.... 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 so 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 wheatpaste, 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 wheatpaste.... 4.2 (add lime, remove wheatpaste & borax) [checks hypothesis 3] follow recipe 4.1, but do not add wheatpaste..... 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 wheatpaste.... 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 wheatpaste.... 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 wheatpaste.... 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 wheatpaste.

'Decision' Test Results for Manure Plasters.... After Brush Test, Best to Worst: 4.5; 4.3; 4.4; 4.6; 4.1; 4.2; 4.... 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....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 Earthlime Plaster Recipes:5. 3/4 cup clay, 3/4 cup sand, 3/4 cup lime putty, roughly 3/4 cup straw, 1 pinch wheatpaste.... 5* (no lime to check hypothesis 1) 1 cup clay, 3/4 cup sand, roughly 3/4 cup straw, 1/2 cup wheatpaste, 1/8 cup borax.... 5.1 (no wheatpaste, check hypothesis 3) follow recipe 5 but add no wheatpaste.... 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 wheatpaste....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 wheatpaste.... 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 wheatpaste.... 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 wheatpaste.... 5.6 (increase straw) 3/4 cup clay, 3/4 cup sand, 3/4 cup lime putty, roughly 1 cup straw, 1 pinch wheatpaste.... 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 wheatpaste.

'Decision' Test Results for Earthlime Plasters.... After Brush Test, Best 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.... 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.... 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.

3. Coversion of Final Decision Recipes to 1 gallon ratios

Recipe for plaster # 2@ 1 gal: 3/4 cup lime putty x 16 cups (1 gal) = 48/4 = 12 cups

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

recipe for plaster # 4.3@ 1 gal: 3/8 cup clay x 16 = 48/8 = 6 cups

3/8 cup manure becomes 6 cups

3/8 cup lime putty becomes 6 cups

3/8 cups straw becomes 6 cups

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

1/8 cup wheatpaste x 16 = 16/8 = 2 cups

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

3/4 cup lime putty becomes 12 cups

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

3/4 cup straw becomes 12 cups

1/8 cup wheatpaste becomes 2 cups

4.  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.  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 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.  

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1 gallon apple cider vinegar- $3

plastic float with sponge blade- $5

trowel- $4

plastic mud pan- $5

2 cheap 3 inch brushes - $8

chemical resistant gloves- $9

notched trowel- $4

notched spreader- $oo.79

construction sponge- $5

nice 3 inch brush for finish- $15

35 gal metal trash bin- $26

organic wheat flower- $4

thrift store sheets for drop cloths- $8

pigments from ceramics shop- $12

paint roller and 3/4 inch nap cover- donated by CCAT

straw bale- donated by Miles Danforth

4-5 ripped bags type S hydrated lime- donated by Hensel's Supply Co., Eureka CA

about 50 gal mixed grade construction sand- donated by Piersons Lumber, Eureka CA

about 25 gal manure- donated

protective goggles- supplied by CCAT

burlap, mason jars, 5 gal buckets, plastic window, screws and driver, rags, hand drill, shovels- supplied by CCAT

chemical resistant cover-alls and jacket, previously owned, bought used about $35 (damaged from rough wear but still serviceable)

heavy work boots- previously owned, $115 (nearly destroyed during project)

gasoline for multiple supply runs- I'll guess +/- $15

grand total- $272.79 plus living expenses and opportunity costs 

I was to get reimbursed through the school but my project was in the summer and then I needed to move, so I swallowed the costs, however, not to despair, they were stretched over several months so not overly painful.  

Thanks also to the CCAT garden which I was invited to graze from.



Continued.... == CCAT Natural Exterior Paint and Plaster, part two