Thin Fiber Concrete

 
 

 

     Thin fibrous concrete is really showing its stuff nowadays, mainly because they want to sell you the fiber. But natural fiber you can get cheaply or even for free can be just as exciting and useful for the home do it yourselfer.

     Fiber adds tensile strength to Portland Cement. Alkali-resistant glass fiber makes some pretty fancy things. Natural fiber can too. However, it’s hard to sell stuff, that folks can get for free. However, if you’re industrious, you can use the free fiber to build exciting things for yourself, and do it on a budget.

     I’m making tests to prove it.

     These pictures show what fibrous cement can do, and if you have the money, below is listed a group of links for you to find out about it. However, if you are willing to take responsibility for your own creation, and make your own tests, I’ll tell you how. There are 2 ways to gain strength in concrete, that will allow you to build unusual thin structures, even a big pink froggy on a lily-pad, you can live in. The first way is to add fiber to your cement mix. And, the second way is to gain strength through shape. Ordinary reinforced concrete does that too. By selling you massive amounts of concrete plus steel rebar. But inside the finished product, it still boils down to tensile strength the steel, compression (the sand and gravel), and shape. Take a look at this picture.

     A piece of cloth is hung by its edges, and then Portland Cement, which you can get reasonably cheap, is placed on top. When cured, and turned upside down, all of the tension becomes compression. And the cement, even stucco, which is sand plus cement, takes up the force. The result is a barrel vault, or roof for your project, if you wish. However, it’s only 2 dimensionally stable. It really needs to be 3 dimensionally stable to function the best for you. That means that you need to curve it 2 ways, like a ball, dome or yurt. Pigs aren’t square for a structural reason. Their curvature is 3 dimensionally stable, automatically.

     Back in the ‘70s, they came out with fibrous stucco that only needed to be 1/8-inch thick, and placed over the white expanded-polystyrene insulation board. You could cover a big long wall and it wouldn’t crack. And hit it with a hammer, and it wouldn’t break. That was a start.

     Now they still want to sell you a product, so they make it a little thicker, add curvature, now it really is super. You can do that too with natural fiber and your own labor.

     However, some natural fiber also has sugar in it, and that slows down hydration, that is, the curing of Portland Cement to make hard “instant” stone. It takes a while longer. That’s one of the reasons it hasn’t been commercialized. It’s different with each fiber type, because each one has a different amount of sugar. While it may be hard to standardize or sale, if you do your own testing, you can find out how the Natural Fiber you choose works.

     By testing, you can find out if the material you’ve chosen is strong enough for your project, and learn how to work with NFRC. Then you will have confidence in your creation.

     The vaulted roof had one problem. It has material on only one side. Now the fibers in the concrete mix may work well, but sheet rock has strong paper on both sides, then when its turned up-side-down, it still has fiber to take up the surface tensile force.

       To the right, is pictured an 1848 concrete boat.

       There are several ways to form a compound curve. One is to hang material from a circle. The material automatically balances the tension, and wipes out the compression. Then when it’s cured and turned upside down, all the tension becomes compression, which works real great with concrete, especially with sand in it, (Stucco.) It’s called a “catenary” or “gumdrop dome.”

       It’s really strong. It still has tension, but it appears at the bottom of the dome and can be handled with a single tensile member. The problem is getting inside the live-in size droopy cloth. To trowel in the cement. Laying it flat is not practical, because when you pick it up, it doesn’t form a compound curve easily. Neither does flat woven cloth.

       You could put up a tent, and then cover it with NFRC. Usually the tent stays with it.

       Another way is to have a movable form, that you can use to make a portion of the finished product, and when that portion is hard enough, move the form to the next location.

       A blow-up form can be used. Like a balloon, the flexible form is blown up with air, and the NFRC is laid on top of it. When cured, the form is deflated and removed. Weather balloons are very large, parade and hot air balloons are too.

       They carve clay into an internal mold for automobiles. But it’s usually only used once.

       Ferrocement boats have been built by making a large pile of sand, placing the ferrocement over the top and then just turning it over and sweeping out the sand when it’s hard.

       A similar thing can be done with waded up newspaper.

       Pieces can be formed horizontal, and then when hard, connected in a vertical position. Geodesic domes can be formed this way.

       A large object such as an automobile can be draped with plastic drop cloth, and then covered with NFRC.

       Igloos are made to be self-supporting from the bottom up so only the very top is difficult to put in position. Of course they are also made of blocks rather than thin walled material. And they are like show tires, that melt in the spring!

       You could spray the outside, and when the ice melts you’d have the finished product. The hard part is finding a spray material that works well at such temperatures. However, frozen sawdust, melts first on the outside, then your project only has sawdust on its interior.

       Another method of forming just about any shape, is with a “Rotomold.” Almost any hollow shape can be rotomolded, even with fibrous cement. However, an object large enough to live in, is usually too big, and the mold can be difficult to make. kayaks are made this way.

       A “master” is first of all made out of inexpensive material, like paper or cardboard. Then a layer of fiberglass is laid over the outside surface, and made so the finished fiberglass can split in half easily to get the finished products out. Then the form fiberglass is sent to a foundry where it is duplicated in aluminum (for a price.)

       It is one of the least expensive methods of mass production. In theory, the Rotomold could be made of NFRC. If you intend to mass produce hot melted plastic, you’ll have to use refractory cement that can withstand higher temperatures. But regular NFRC should work fine at lower temperatures.

       But the process involves rotation, so whatever material you intend to mass produce, you must rotate it until it gets hard.

       Paper Maché floats are probably the easiest for hand work. First an “armature” (they call it that because it stays inside the finished product,) is made of chicken wire, (poultry netting,) bent into the final complex curved shape. Then the paper and glue (fiber and Portland Cement in the case of NFRC,) is laid by hand over the armature surface, and left to dry, (cure.)

       All natural fibers require some manufacturing. This includes fibers made of natural basalt, such as those from the Ukraine. These have the advantage that they don't rust or are affected over very long times.

       How many ways can you dream up? Which ones will work best under your circumstances? Send me the pictures. Please read all my other articles for further information.


Valuable Additional Links:

  1. formfindinglab.princeton.edu
  2. theconstructor.org
  3. www.tumblr.com
  4. thearchitectsarchive.blogspot.com
  5. www.sobenboard.com
  6. concretely.blogspot.com
  7. www.umanitoba.ca
  8. en.wikipedia.org/wiki/Stucco

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