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La Yuca schoolroom renovation/Literature Review

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Literature Review[edit]

See La Yuca schoolroom renovation page for project details and description.

Climate[edit]

The Dominican Republic has a tropical climate, which must be considered when choosing building materials and methods. Average temperatures in Santo Domingo range from 75 °F in winter months to 81 °F in summer months. There is not a lot of fluctuation in temperature in Santo Domingo. The average minimum temperature for the last 8 years was 68 °F and the average maximum was 90 °F. It rains about 3-4 days per month from December to April, and 5 days per month from May to November.[1] The Dominican Republic is located in the Caribbean hurricane area. Hurricane season for the Caribbean is from June to November, but most hurricanes occur in the Dominican Republic in August or September. [2]

Alternative Plaster[edit]

The plaster previously used on the walls was a mixture of sand and cement with more sand than cement[3]. This plaster now has cracks and needs to be refinished.

Basic Materials[edit]

Natural plasters usually have 3 components:

  • Clay - Fine earth particles that help the plaster adhere to itself and to the wall.
  • Sand - Provides compressive strength.
  • Fiber - Provides tensile strength. [4]

Lime[edit]

Lime is a natural building material that can work well in tropical climates. It has a high porosity, which allows it to breathe and expel standing moisture. Lime has a high pH, which makes it naturally resistant to mold. Lime can heal itself if it has a few small cracks, rather than a few large cracks, if water enters the cracks and dissolves some of the free lime. The lime is deposited in the cracks when the water evaporates and fills the cracks with the new lime.[5]

Coats[edit]

  • Slip Coat: The first layer applied to the wall. It consists of clay and water and should have a consistency that is between cream and cake batter. Apply by hand.
  • Infill Coat: Consists of 0.5" screened clay, fiber, and sand. If a fiber like straw is used it should be chopped finely. A little bit of flour paste can be added for better consistency (more stickiness), and a little bit of lime (about 0.5 cups for a wheelbarrow of infill) can be added for extra mold prevention. Apply using trowel.
  • Finish Coat: Consists of 0.25" screened clay and sand. It is recommended to add flour paste to this layer, so that enough sand can also be added to avoid cracking, but maintain the stickiness of the finish. This will be the base coat of the paint if paint is going to be applied to the wall, so color should be considered accordingly.[6]

Sawdust[edit]

In Las Malvinas an ecoladrillo schoolroom was built using sawdust as a filler in the plaster. The recipe included 4 parts water, 1/4 part lime, 4 parts sawdust, 3 parts sand, and 2 parts cement. Of the 3 layers applied, the third layer had the most cement, and also included iron oxide for color. It was hard to apply the sawdust mixture to dry concrete, so cement had to be cut into the mixture at contact points with columns and beams. The interior of the schoolroom has some minor cracks, but looks better than than walls in La Yuca's schoolroom, which used just sand and cement. [7]

Natural Paints[edit]

  • Clay: A clay paint can be made by combining cooked flour paste (diluted with water) to clay. A colored clay can be used, or white kaolin clay can be used with desired pigments added.[6]
  • Casein: Casein paint is made from milk curds. It must be combined with lime or borax, water, and a filler. Casein can be applied to a wide variety of surfaces, lasts a long time, and is non-toxic.
  • Flour: Flour paints are simple, versatile, and can work with more variation in the recipe than most other natural paints. Flour paint is non-toxic, and can be applied to almost any surface. A typical flour paint consists of flour, water, clay, and mica (or other fillers).[8]
  • Egg: Egg paint is made from a combination of eggs, linseed oil, and water[9]. Egg paint must be combined in precise quantities for correct emulsification, and it would be expensive and slow to paint large walls with it.[10]

Ventilation[edit]

The current structure allows copious ventilation, but leaks too much water into the classroom.

Natural Ventilation[edit]

Natural ventilation is a process designed to utilize naturally occurring phenomena to regulate indoor temperatures. The natural phenomena primarily utilized are wind and atmospheric buoyancy (temperature and/or humidity-induced). By using natural ventilation rather than mechanical, total energy consumption is reduced significantly. These natural systems rely on pressure differences caused by wind or the buoyancy effect to move the air, also dependent upon size and placement of ventilation openings.[11]

Buoyancy Induced Ventilation[edit]

Buoyancy ventilation provides two forms of ventilation to produce the buoyancy effect. These forms are: temperature induced (stack ventilation) and humidity induced (cool tower). Temperature induced ventilation involves letting in cooler air on the ground level of a room while the warmer air is excreted through the roof or installed chimney. A chimney provides more effectiveness through being heated up by solar energy and accelerating the stack ventilation effect. This method is generally most effective in colder atmospheric conditions. [11]

Natural Ventilation
Figure 1: Stack Ventilation/Wind Ventilation: The cooler, more dense air enters through a lower opening in the room and the warmer, less dense air exits through a more elevated opening. This illustration involves the wind ventilation aspect as well, but the concept is the same.[12]

Humidity induced, or cool tower, ventilation is the use of a constructed tower to evaporate humidity from the air causing the drier, less dense, and cool air to fall. This type of ventilation is most effectively used when paired with stack ventilation, as the cool air is moved into the stack ventilation system. Cool tower ventilation is most effective in low humidity environments.[13]

Wind Induced Ventilation[edit]

Wind-based ventilation systems consist of creating openings in a building on the windward and leeward sides. The higher pressure, cooler, wind enters through the windward opening and the warmer air in the building, with the continuing wind flow, exits through the more elevated leeward opening (See Figure 1). The building would require consistent and adequate wind flow for wind induced ventilation to be a viable option.[11]

Cool Roofing[edit]

Cool roofing entails design and construction techniques to enable roofing to play a part in lowering the temperature inside the room(s) below. Utilizing cool roofing techniques allows low embedded energy costs and is more economically viable than installing conventional air-conditioning systems. There is no continual energy usage with reflective roofing and this strategy works well with natural ventilation strategies. This type of roofing is viable on low-slope or flat roofing, such as the schoolroom in La Yuca.[14]

Reflective Roofing[edit]

Reflective roofing is the use of materials that reflect infrared and ultraviolet rays as a means of cooling the building below. This can be done through the use of light colored or “spectrally selective” paints, bare metal roofing, or tile roofing. Designing a layer of roofing with highly reflective properties lowers the heat absorption of the roof and consequently results in less heat transfer to the building below.[15]

Paints[edit]

Light colored paint (white in particular) has been shown to be most effective, but “spectrally selective” paints allow users more aesthetically pleasing choices with moderately less reflective efficiency. Spectrally selective paints have shown to be capable of more than 20% higher reflectivity than non-specialized paints of the same color.[15]

Bare Metal Roofing[edit]

“Unfinished galvanized steel or ‘tin’ roofs are” the most commonly used materials for reflective, bare metal roofing. These metals are initially highly reflective, but as they age their reflectiveness drops significantly. In order to counteract this drop in reflectivity on galvanized steel roofing, a white coating of paint can be applied for a substantial increase. Alternatively, Galvalume (an alloy of aluminum and zinc) is more effective as reflective metal roofing due to its ability to maintain reflectiveness as it ages.[15]

Tile Roofing[edit]

Light colored tile roofing is another option for reflective roofing, but it does not outperform light-colored metal roofing. The shape of the tile has a miniscule effect on cooling conditions, but a light coloring or spectrally selective paints must be applied for worthwhile effectiveness.[15]

References[edit]