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Difference between revisions of "Las Malvinas ecoladrillo schoolroom 2012/Literature Review"
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Revision as of 05:44, 30 July 2012
- 1 Literature Review
- 1.1 Climate
- 1.2 Earthen Flooring
- 1.3 Alternative Infill
- 1.4 Structure
- 1.5 Natural Paints
- 2 References
See Las Malvinas ecoladrillo schoolroom 2012 for the project that this research was completed for.
The Dominican Republic is in a tropical climate zone, where rainfall varies seasonally but temperatures are relatively static,  ranging from 64 to 90 degrees Fahrenheit year round. The rainy season begins in early summer and lasts through mid fall, with the the most powerful tropical storms occurring during August and September. The average annual rainfall is 150cm, much of which falls on the northern side of the island. This results in cooler temperatures and higher humidity in comparison to the south.
An earthen floor is made up of four basic layers. A layer of substrate dirt or sawdust that is laid down on top of a layer of fine gravel, which is then covered with a layer of clay or sand and sealed with a layer of hemp or linseed oil. The result is a porous, supple and durable floor which can be made for less than a dollar per square foot. (including labor).Rammed earth is a style of earthen floor that uses tamping or ramming to compact and harden the layers. Specific ingredients and construction methods vary by location. The overarching idea is to add water and stabilizing agents like sand and straw to dirt, which is then compacted until hard. Once dry, seal it with an oxidizing oil like linseed or hemp oil. 
For a general rammed earth floor, the first step is to lay down a plastic moisture barrier sandwiched between two thin layers of sand, followed by 4 to 6 inches of compacted "road base mixture."
- clay, sand, and various types of gravel (ratio unimportant)
It is important to tamp the floor and sprinkle it with water every additional few inches to ensure good and even compaction. The next step is to add a one inch layer of standard earth plaster mix.
- 6 parts sand, 2 parts clay, 1 part finely chopped straw
The plaster should then be troweled smooth and allowed to dry. Once dry, the final step is to lay down four layers of linseed or hemp oil, allowing each layer to dry before applying the next. The last three coats of oil should be mixed with increasing ratios of citrus paint thinner. 
To get the right mix, experiment with a test area of at least 3x3 ft. The mix should be strong enough that it is not powdery when it dries, and it must contain enough fiber so that there are no cracks. Apply the mixture with a trowel in 1/2-3/4" layer. The material should come off cleanly and easily as you move the trowel across the sub-floor. If it sticks, there’s either too much clay or not enough moisture; if it won’t stick to the trowel, there’s either too much moisture or not enough clay. 
Homeowners in a wet climate should put down several inches of gravel to enhance drainage. This can be a three- to four- inch layer of clay, sand, and gravel or crushed stone, on top of which lays the half-inch layer of finer mix. If you pour this supportive layer in a damp state—and even add lime to the mixture—it will dry and harden more quickly.  A typical earthen floor might include a 2.5-inch base layer of 70% sand, 30% clay, with handfuls of long straw for tensile strength. Once it is dry, the final layer will be installed and smoothed with a trowel, composed of a similar sand to clay ratio, but mixed with very short chopped straw. 
Linseed Oil Coating
Increasing amounts of paint thinner in the linseed coatings allow deep penetration of the oil into the floor:
- 1st coat - Only linseed oil
- 2nd coat - 3:1 linseed to paint thinner
- 3rd coat - 2:2
- 4th coat - 1:3
Boiled linseed oil contains solvents and is highly toxic, while eco-friendly linseed oil can be expensive. “As a compromise, we take raw linseed oil and put it in the sun in shallow pans covered with a piece of glass, leaving a tiny air space. The oil pre-oxidizes and dries faster. It’s called sun-thickened oil.” 
The main categories of binders used for earth construction are Portland cement, lime, bitumen, natural fibre and chemical solutions such as silicates. Benefits of cement addition is improved structural integrity, while a downside is reduced permeability of earthen mixture and thus natural ability of earth to allow passage of moisture throughout the soil mass is reduced.  Tests have indicated that there is an optimum lime dosage for a soil beyond which compressive strength decreases. The likely dosages are between 6-12% lime by dry weight and will increase as clay content increases. 
Infill is used in conjunction with frame or post-and-beam style structures to fill in the wall spaces. In such styles, a wood frame or concrete column and beam structure is used to hold up the roof and provide structural support, while the infill is used to seal the building from the elements, as well as provide thermal mass and insulation. Infill is usually considered non-structural, however it can increase lateral support depending on the type. 
“Eco-bricks” are a method of alternative infill that use plastic bottles and trash in the bulk of their composition. Bottles and trash are stacked and compacted into a wood frame and held secure by a layer of chicken wire on each face. The two faces are then plastered smooth. Any inorganic waste material can be used to fill the bricks, however ideal materials are those that cannot be recycled others. Examples include: food packaging, old socks, razor blades, used up pens and markers, clothing tags, cotton swabs, etc. The process of "up-cycling" such materials that would otherwise end up in the trash reduces waste and significantly cuts construction costs. 
That being said, not all trash makes for good infill material. Anything organic such as food waste will not work. Trash must be clean and moisture free, as well as the bottles, and it is best to stay away from paper waste if at all possible. It is also important to stuff bottles as full as possible to increase insulation. Training of community members about these material requirements is important to ensure a stable and safe structure.
Papercrete is a method of building traditional style cinder blocks out of paper. Soaked and shredded paper is mixed with sand and a binder such as Portland cement or clay, and then compressed into a block mould. Papercrete blocks can be stacked and mortared with papercrete mortar and used as a substitute for traditional concrete blocks. 
The type and quality of paper can vary depending on availability. Newsprint or office paper is ideal, but any grade of paper that can be re-pulped will work. Paper that is waterproof and/or has a wax or plastic component such as butcher paper, cardboard, and juice cartons cannot be easily separated in water and will not work. 
The ratio of sand is dependent on the needs of the papercrete. A mix with more sand and less paper will dry faster, shrink less, and have more thermal mass and compaction strength. A mixture with more paper and less sand will be provide more insulation and will have more tensile strength, reducing the need for re-bar or other types of tensile supports. If your source of paper is free, more paper will also reduce material costs.
Disadvantages to papercrete in comparison to traditional concrete include:
- Longer drying time, especially in humid climates
- More vulnerability to fire
- More vulnerability to mold growth
- More vulnerability to water damage
Advantaves to papercrete include:
- More dimensional stability under different types of stresses
- Significantly lighter than traditional block
- High insulation (R-value of 2 per every half inch)
- Resistant against rodent and insect infestation
When considering sawdust as a building material, there are functionally two different types wood: hardwood and softwood. The quality of the sawdust will vary depending on the species, but most hardwoods are relatively better than softwoods at absorbing water, which are typically harder and grainier. For this reason, sawdust gathered from hardwoods is more ideal. Sawdust can be used in mixes with clay to make adobe and cob or with cement to make concrete and plaster substitutes. It can provide insulation, protection against freezing. It can also be found for free.
Cob and adobe are made from mixtures of clay, sand, lime, sawdust and/or green waste. The ratio's can vary greatly depending on availability and quality of materials, making cob and adobe very adaptable building materials. Because Las Malvinas has an abundance of sawdust, the ratio with the most potential requires 9 parts sawdust, 3 parts clay, 2 parts lime, and 1 part sand. The sawdust is soaked overnight and dried for a few hours, then mixed by hand or by hoe with the rest of the mixture and water. The amount of water need varies depending on the moisture content already present in the clay. The mixture can be made into adobe bricks or built up in monolith. Cob or adobe made with more sawdust rather than green waste will also dry faster.
A mixture of sawdust, sand, and cement can also be used in infill. The mixture requires less cement than concrete or traditional cement plasters, however there is little information regarding its structural integrity. The common ratio is 3 parts sawdust, 2 parts sand, and 1 part cement, and the final mixture can be used as a plaster over another alternative infill material such as eco-brick.
The structure of a building is there to provide support and stability against the compressive and tensile forces acting on it, both from the dead weight of the building itself and from external stresses such as wind, rain, and earthquakes. There are multiple methods of structural construction, but all of them must meet the same three basic criteria:
- Structural members must be strong enough
- Structural members must be joined properly
- Final Structure must be rigid
The degree to which each criteria must be met depends on the needs present, the resources available, and the expected forces. 
Post-and-beam style construction is a widely used and trusted method of structural building. In this style, concrete columns or wood posts are spaced up to eight feet apart and used as compressive members. The diameter and spacing of the columns/posts are dependent on each other.
- Larger spacing requires larger diameter columns/posts
- Smaller columns/posts requires smaller spacing
These compressive members are hammered into the ground or supported by concrete foundations, the depth of which are dependent on the height of the columns/posts. A general rule for single story structures requires 3 feet of depth for 8 feet of height.
Corrugated Tin Roofing
Corrugated tin roofing is commonly used in tropical areas because of its durability, sturdiness, and light weight design. The key attribute leading to the ability to remain useful for so long is due to the special corrugated shape the metal is formed to.  Main types of metals used are aluminum, galvanized steel, copper, aluzinc, and tin.  Integrated ventilation is very important since this style of material if often used in tropical, humid climates. It is meant to provide insulation from heat during most of the year, so to "provide generous wall openings, large doors and windows" is key during the construction of the roof. 
Natural paints are non toxic naturally derived alternatives to traditional synthetic household paints. Their non toxicity reduces exposure to harmful air pollutants such as volatile organic compounds (VOCs) that off gas from traditional synthetic paints, and many natural paints are biodegradable and compostable. There are many different compositions of natural paints and examples of success for each, however there is little legitimate resistance and durability performance data on any of them. Therefore it is important to test each composition thoroughly before application.
In synthetic paints as well as natural paints, there are four basic ingredients:
- Fillers (for bulk and/or texture)
- Solvents (such as thinners, biocides, and drying catalysts)
Natural alternatives to solvents are generally not as proficient as those used in synthetic paints. Therefore natural paints often take longer to dry and are typically not as smooth or durable against degradation as synthetic paints. This is not universally true and different compositions will have different strengths and weaknesses as well as different aesthetics. 
Preparation and Tools
Because there is so little data on natural paints, time and resources for testing are important. Consistency and shade is important and difficult to replicate over multiple mixes, therefore it is crucial to work out the exact quantity of paint needed for the planned area. This requires knowing the absorbency of the surface being painted, the thickness of the paint, and the number of coats needed. Keeping a detailed record of the testing process is highly recommended.
The most important tool to acquire is a good brush. Something with a densely packed head and long stiff bristles works well for mixing paints and breaking up dry ingredients. Alternative application devices such as sponges and rollers are also important to have. They allow for more experimentation with the aesthetics, and different application techniques will work better for different natural paints.
Egg tempera is composed of raw egg and boiled linseed oil. Any natural pigment can be used to achieve the desired color, and unlike most natural paints, egg tempura paint dries in about an hour. It has a glossy finish, can be used indoors or outdoors, and can last for over 20 years.
Casein paint is composed of nonfat milk, lime, and some type of filler and pigment. The mixture can be applied indoors or outdoors to all types of surfaces (wood, stone, drywall, wallpaper, earthen plaster, masonry, previously painted surfaces, etc). Casein Paint is also fungi resistant, compostable, and long lasting.
Water Based Paints
Water is the the most commonly used natural alternative to synthetic solvents. Distemper is a water based paint composed of chalk and rabbit skin glue. The mixture works best with pastel pigments and its thick texture presents unique aesthetic opportunities. Limewash is a water based paint composed of lime putty and pigment. It is thick and chalky like distemper but with increased durability and antibacterial properties. 
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