CCAT earthbag garden terrace

Welcome to the page for the CCAT Earthbag Terrace, located in front of the Campus Center for Appropriate Technology at Humboldt State University.

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Background

The Campus Center for Appropriate Technology (CCAT) is located near the Behavioral and Social Sciences building on the Humboldt State University campus in Arcata, California. Our original project idea was to build a small informational sign wall to welcome students to the northern entrance to CCAT, and alert readers to upcoming events hosted at CCAT. Due to bureaucratic rigamarole, this project has been changed to a natural plastering project on the CCAT grounds. This project's purpose is to provide a sturdy, natural plaster covering to the EarthBag gardening terrace being built in front of CCAT.

This project is to be completed during the Spring 2012 semester of ENGR 305 class by Danielle Burkhart, Morgan Murphy and Cody Hill. Describe the background of the project. Make sure to cover who, what, why, when and where. You will want to write in word (to have a local copy and help with grammar) and then copy it into the edit window on Appropedia.

Problem statement

The objective of this project is to protect the EarthBag terrace at CCAT from the elements and add an aesthetic element by layering natural plaster over the wall to give it an adobe effect. Start your project objective statement in the format, "The objective of this project is to...." Eventually you will list criteria here as well.

Criteria

Criteria	Constraints	Weight
Structural Stability	Must withstand Arcata climate and the elements for a period of no less than 10 years.	10
Effectiveness	Must reflect the values and culture of HSU/CCAT.	9
Cost	Should cost as little as possible.	8
Embedded Energy	Construction should be less embedded energy than traditional wall construction.	7
Materials Quantity	Must be as few as possible, with as little waste as possible, without compromising structural integrity.	7
Administrative Review	Proposed method must meet requirements for CCAT approval.	9
Aesthetics	Must be visually attractive, complementary to surroundings and must demonstrate natural building technique.	10

Literature Review

This is a review of the available literature pertinent to the EarthBag Terrace at CCAT.

EarthBag Basics

The gardening terraces in front of CCAT are being constructed from EarthBags and barbed wire. The EarthBags are polypropylene bags filled with a mix of on-site soil and clay soil from a local landscaping company. Containing about 5%-25% clay,the soil is moistened then transferred to the bag. ^[1] The bags are sewn shut with bailing wire then laid like bricks in courses, with barbed wire acting as the mortar to grip the bags and hold them in place. The soil is compressed and hardens as it dries. Earthbags are not extensive or costly, they are user-friendly and can be built on a variety of foundations. ^[1]

Earthbag Advantages[1]	Earthbag Disadvantages[1]
Requires no power tools	Getting approval may be difficult
Easy to learn, simple	It's a new technology so you are a guinea pig
Suitable for many different climates/regions
No precise soil mixture, you have wiggle-room
Earthbags are thick and lend themselves to passive solar design

Erosion

Since the garden terrace will not incorporate a covering to protect the plaster from the large amounts of rainfall native to Humboldt county, an other approach must be employed.

-"A mixture of alum and water and a mixture of soap and water are alternately mopped onto the surface of a lime-plastered surface. This method of water resistance has been used effectively in Mexico for decades. Usually applied to parapet tops, horizontal surfaces, and domes, several alternating coats will give ample protection for many years."^[2]

Plastering

All 4 types of plaster have their disadvantages. Like cement plasters, the natural plasters require 3 coats of plaster to be complete.^[1]

"Fat Plaster"

"Fat plaster is strong, durable and easy to apply...The combination of three distinct sizes of well-graded fiber mixed with a typical plaster soil of (approximately) 25% clay and 75% well-graded sand has produced a srong crack resistant plaster."^[2] -"...a single coat of piping hot, boiled linseed oil can be used a sealer/stabilizer over a fat plaseter to inhibit mold and extra resilience"^[2].

Lime-Based Plaster

The major ecological concern for lime-based plaster is due to the quantity of material extracted from individual sites. Lime is manufactured by heating limestone, chalk or shell deposits to a high temperature. When CO₂ is involved, the end-product is quicklime which is combined with water to produce slaked lime which, when made into plaster, absorbs atmospheric CO₂ while hardening.^[3] Some builders apply two coats of earthen plaster before a final coat of lime plaster. The lime plaster allows the wall to breathe. The lime naturally becomes water resistant over time as it hardens, and is easy to repair. For building use, always use builder's lime mixed with water to skim milk consistency. Lime is caustic, so protection is important when working with lime.^[1]

>"...it can take many decades for the lime binder in lime plaster to convert substantially into calcium carbonate. However, if the plaster has been adequately protected during the period of substantial carbonising, for example by application of limewash(lime mixed with materials such as tallow and linseed oil)every couple of years, the resultant calcium carbonate has very low solubility in water and therefore little tendency to weather". (Practical straw bale building. Collingwood VIC, Australia: Landlinks Press, 2005)

>"Lime plaster...is typically applied on exterior walls where it provides excellent protection against the elements".(Cedar Rose Guelberth, and Daniel D. Chiras, The natural plaster book: earth, lime and gypsum plasters for natural homes, (Trancontinental printing: canada, 2003), 12. )

Lime plaster is an extremely durable and highly protective wall surface. its ability to permit the escape of water vapor within its walls makes it an ideal in rainy climates. in dry climates the walls must be misted up to three times a day for a few weeks so the lime does not dry out too quicky. if it dries out too quickly it will weaken the material and can cause it to crumble off.^[4]

Read more: http://www.motherearthnews.com/Do-It-Yourself/2003-02-01/Perfect-Plaster.aspx?page=4#ixzz1mDtFNkqh

Gypsum-Based Plaster

Make sure to include description, advantages and disadvantages, and/or have a comparison matrix. Made from Calcium Sulfate, which is now produced as a by-product of scrubbing Sulfur Dioxide out of power station emissions.^[3]

Gypsum is composed of the mineral calcium sulfate. It is widely available and easy to work with, you only have to mix it with water before applying. It is most effective in two coats. Gypsum expands as it dries so it eliminates cracking. small hairline cracks might happen but it is easy to fix, just smooth it over with a wet sponge. Gypsum is too water souluable to put on exterior walls and will melt away in rain or wet climates.^[5]

Cement-Based Plaster

The environmental concerns surrounding this type are due to the process by which cement produced, which emits intensive amounts of CO₂ as well as metals and sulfur oxides into the atmosphere.^[3] Earth based plasters must 'breath' or have a humidity exchange with the surrounding atmosphere to lose water absorbed from the surface. Cement plasters make it difficult for this to happen. Cement plasters are waterproof and wil not allow for necessary breathing of the earth wall. This will lead to a buildup of moisture between the plaster and the wall which will create the plaster to crack and crumble off exposing the natural wall underneath.^[6]

Project Costs (in Progress)

Quantity	Material	Source	Cost ($)	Total ($)
1 yd3	Clay	Local Source	18.00	18.00
1 yd3	Sand	Local Source	36.00	36.00
1 yd3	Lime	Local Source	17.00	17.00
1 yd3	Pigment	Local Source	free	0.00
1 yd3	Soil	Local Source	39.00	39.00
Total Cost				$110.00

References