Abstract

Objective

The objective of this science fair project is to determine whether straw bales are a viable alternative building material by performing a water resistance test.

Introduction

Have you ever thought about the components of buildings? Steel, wood, concrete blocks, and insulation. These are conventional building materials that are used to build most commercial and private buildings. However, there is a new way of thinking about building structures. The Green movement promotes constructing buildings out of materials that are composed of renewable, rather than nonrenewable, resources. Alternative and green building materials can be made with virtually anything—from recycled plastics, such as plastic milk containers and plastic bags, to old wood from demolished buildings, which reduces the need to cut down trees. Old shredded jeans can be used as insulation, instead of fiberglass. This kind of insulation can use up to 85 percent recycled denim and cotton fibers. Some people even use old car tires to build their homes!

Another alternative building material is straw bales. A straw bale is straw that has been compacted and tied into rectangular shapes. Straw is a byproduct of growing grain, so it is available in most parts of the United States. An advantage of straw bales is that no trees need to be cut down. It also has tremendous strength under compression, and has a high R-value. The R-value is a measure of an insulator's ability to resist heat flow. The R-value of a straw bale is 3.1–3.7 per inch. This is comparable to the R-value of fiberglass insulation, which is 3.2–3.6 per inch. You can do additional research to find out more about the R-value scale. In addition to being a good insulator against weather elements, straw bales are also good sound insulators.

Issues that some may have with using straw bales as a building material include the perception that straw bales are fire hazards and may rot or decompose due to moisture. Since straw bales are very tightly bound, they are not a fire hazard. Fire needs oxygen, which is not available in tightly bound straw bales. Moisture, however, is a problem. When picking out straw bales, the builder needs to make sure that the moisture content is below a certain level, that the straw is yellow and not brown or wet-looking, and that the bale is tightly bound and keeps its shape.

Click here to check out the video "Straw House by Brenett, Kim, Lucretia and Omney." This video was produced by DragonflyTV and presented by pbskidsgo.org.

In this science fair project, investigate whether straw bales are a viable construction material for homes. This science fair project is based on the DragonflyTV episode "Straw House by Brenett, Kim, Lucretia and Omney." Click the link on the right to see how these girls tested their stucco and straw block. You'll also make stucco and straw blocks and water test them, just like the girls in the episode did. Feel free to be creative and come up with other tests, too. For example, you could test the sound-insulation properties of straw bales compared to other building materials. Check out the Variations section, below, for ideas how.

Terms, Concepts, and Questions to Start Background Research

• Green movement
• Straw bale
• Compression
• R-value
• Insulator

Questions

• What are some alternative and green building materials?
• What are some advantages and disadvantages of using straw bales in buildings?
• What is R-value and what is it used to describe?

Bibliography

• Wikipedia Contributors. (2008, October 30). Straw-bale Construction. Wikipedia: The Free Encyclopedia. Accessed October 30, 2008, from http://en.wikipedia.org/w/index.php?title=Straw-bale_construction&oldid=248382885

The following website is written by a straw bale builder. It has some very interesting facts and information about building with straw bales.

• Morrison, A. (2008). StrawBale.com: A World Leader in Straw Bale Education. Retrieved October 30, 2008, from http://www.strawbale.com/

This science fair project was based on the following DragonflyTV episode:

• TPT. (2006). Straw House by Brenett, Kim, Lucretia and Omney. DragonflyTV, Twin Cities Public Television. Retrieved November 3, 2008, from http://pbskids.org/dragonflytv/show/strawhouse.html

This website has a really cool video that shows fire-testing of a straw bale wall. It also has other documents with testing results.

• Ecological Building Network. (2006, March). Straw Bale Test Program. Retrieved November 7, 2008, from http://www.ecobuildnetwork.org/strawbale.htm

Materials and Equipment

• Straw bales, not hay bales (6); available at animal feed stores
• Rags, cotton (6) of approximately the same size
• Stucco mixing tool
• Stucco (2 bags); available at your local hardware store
• Water
• Mixing tray
• Mason trowel
• Cinderblocks (3)
• Sledgehammer
• Safety goggles
• Long pants
• Closed-toe shoes
• Digital timer or stopwatch
• Lab notebook

Experimental Procedure

• Purchase the straw bales from an animal feed store. Note: Make sure to get straw and not hay. Hay is animal food and straw is not.

Preparing the Straw Bales for Water Testing

1. Poke a rag into the middle of the six straw bales. Use the stucco mixing tool to help. You will cover only three of these straw bales with stucco. Set the other three aside. For your testing, you should have:
   1. Three plain straw bales with rags in the middle.
   2. Three stucco-covered straw bales with rags in the middle.
2. You're now ready to start covering three of the straw bales that have rags in them. You don't want your mixture to dry out, so only mix enough stucco and water to do one layer and one straw bale at a time. Mix the stucco and water in the mixing tray with the mixing tool. Follow the instructions on the stucco packaging. You will need to allow plenty of time (about 24 hours) for each layer to dry.
3. Cover the three straw bales with stucco, using the following instructions.
   1. For the first layer, work the stucco into the straw with the mason trowel. You do not want the first layer to be smooth, so use the toothed edge of the trowel to scrape lines into the surface so that the next layer of stucco will have a rough surface to adhere to.
   2. Each layer should be about ½- ¾ inch thick.
   3. Keep in mind as you stucco that one side needs to be resting on a surface, so you cannot stucco that side until the others are dry. Take that into account as you plan the time it takes to do three layers for all six sides, and leave plenty of time for all sides to dry.
   4. Wait approximately 24 hours for each layer to dry. Don't dry the stucco in the sunlight; if it dries too fast, it could crack.
   5. Your stucco-covered straw bales should look like the ones in the DragonflyTV video above.
4. Repeat step 3 two more times for each of the three straw bales, until each straw bale has three layers of stucco. The final thickness of the stucco should be about 2 inches.

Water Testing

1. Now you are ready to start testing. Go to your local stream or creek with all of your supplies and testing materials. Submerge the three stucco-covered straw bales that have rags, the three plain straw bales with rags, and the three cinderblocks into the water. Find a spot that isn't too deep, but that will cover the straw bales and cinderblocks. Let the nine blocks soak for at least 1 hour. Use the timer to keep track of time.
2. Once the hour has elapsed, remove the straw bales and cinderblocks from the water. Remove the rags from the plain straw bales. You may cut them open to do this. Do they appear to be wet or dry? What about the outside appearance of the cinderblocks? Record your observations in your lab notebook.
3. Now make sure that you are wearing safety goggles, long pants, and closed-toe shoes. Take the sledgehammer and break open the stucco-covered straw bales. Are the rags dry? Record all observations about the wetness of the rags and the condition of the stucco-covered straw bales in your lab notebook.
4. Still wearing safety goggles, long pants, and closed-toe shoes, take the sledgehammer and break open the cinderblocks. Are the insides dry?
5. Be sure to clean up all of your test materials before leaving the area. Do not leave any debris near the stream.

Analyzing Your Data

1. Compare your test results. Do you come to the same conclusion that Brenett, Kim, Lucretia, and Omney did in their tests?
2. How do the stucco-covered straw bales, the cinderblocks, and the plain straw bales compare in terms of water resistance? Is there a clear difference in how these materials hold up under water testing?

Variations

• Another important aspect of home building is soundproofing. Build three enclosures with the three different types of building blocks (stucco-covered straw bales, just straw bales, and cinderblocks). Turn on a radio and place it inside each enclosure. Cover the enclosures with a wood roof. Use a sound meter to see if you can detect sound leaking out from the enclosures.
• Test the heat resistance of the stucco straw block and the cinderblocks, as shown in the DragonflyTV video. Is there a difference in the heat resistance between the two? Does the heat resistance of the cinderblock wall depend on how the blocks are oriented to each other? Does it depend on if the cinderblocks are open during testing (as shown in the video)? Perform some tests to find out. If you do decide to work on this variation, then you should perform it in a privately owned location, and you must have two adults monitor the test site, as well as have two fire extinguishers. The test site should be cleared of flammable debris. Do not heat-test the plain straw bales.
• Try to come up with other tests, such as compression-strength tests. What are some characteristics that construction materials need to have? Read the last reference in the Bibliography to help you develop a test.

• For more science project ideas in this area of science, see Materials Science Project Ideas.

Credits

Michelle Maranowski, PhD, Science Buddies

This project is based on the following DragonflyTV episode:

• TPT. (2006). Straw House by Brenett, Kim, Lucretia and Omney. DragonflyTV, Twin Cities Public Television. Retrieved November 3, 2008, from http://pbskids.org/dragonflytv/show/strawhouse.html

Last edit date: 2009-01-04 19:33:00