VOA慢速英语 2009 0112a（在线收听）
This week in our report we are going to talk about adobe. No, not the information technology company in California, Adobe Systems. We mean the traditional building product made of soil and other materials. Adobe is shaped into bricks that are laid one on top of another and used as a low cost way to build walls and houses.
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| Adobe structures at Tumacacori National Historical Park in southern Arizona. The park protects the ruins of three Spanish colonial missions. |
Adobe is soil that contains at least forty percent clay. In its purest form, clay can be shaped and stretched and used to make objects. Clay becomes very hard when it is put in a fire or a special oven called a kiln.
Adobe becomes a sticky mud when it is mixed with water. Liquid adobe mixture can be poured into containers called molds. This way the adobe can be shaped into bricks of the desired size.
Adobe bricks must be dried completely before they are used. This is necessary so that the walls of a building will not shrink or break.
Too much water can make adobe weak. Sometimes other materials are added to the adobe mixture to strengthen it. These materials help keep the water in correct balance with the soil. This will help the adobe resist changes in the weather and humidity.
One material that is commonly added to strengthen the adobe is straw. Straw is the dried stem part of plants such as wheat, millet and sorghum. Straw is especially popular in places where the clay content of the soil is high.
Other materials such as lime and cement can be added to strengthen the adobe. About once a year, houses made from adobe should be given a layer of mud. This so-called paint job helps keep the adobe strong.
Adobe can take a long time to dry and become hard. So the bricks should be made in hot dry weather. If the weather is right, the bricks should dry in seven to ten days.
Many people around the world have found that adobe is a good way to make houses or farm buildings. But people who work with adobe must experiment. They must find the right combination of soil mix, water content and drying methods.
More information about adobe can be ordered from EnterpriseWorks/VITA, an anti-poverty group in Washington, D.C. The Web site is enterpriseworks.org. Click on News & Resources, then the link for Publications.
And that's the VOA Special English Development Report. Transcripts, MP3s and podcasts of our reports are at voaspecialenglish.com. I'm Steve Ember.