ferro cement and frost

Discussion in 'Homesteading Questions' started by Paul Wheaton, Dec 29, 2005.

  1. Paul Wheaton

    Paul Wheaton Well-Known Member

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    I keep thinking that ferro cement can be a great, cheap solution to many things. But it seems that everything I find on it looks like everything might be done where it doesn't freeze.

    Frost and cement seem to have issues. But maybe that's just the old slab style.

    One place where I think ferro cement could really shine is with a cob oven. It needs to be protected from the weather. A layer of ferro cement could do the trick. But if it is one contiguous piece - would it crack with the frosts?
     
  2. michiganfarmer

    michiganfarmer Max Supporter

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    Ive never heard of ferro cement.
     

  3. Paul Wheaton

    Paul Wheaton Well-Known Member

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  4. gobug

    gobug Well-Known Member Supporter

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    Paul
    If I recall, you live in eastern Washington, but I don't know the extremes you face. I have made several ferrocement projects here in CO and have never taken precautions to protect from the weather. I have not seen any damage to date. All of these projects live outside and have endured subzero winter and 100+ degree summers for a couple years. I'm guessing my extemes here are similar to yours.

    Ken Kern wrote a book called "The Masonry Stove" and shows how to build a curvilinear ferrocement stove/oven. He used regular cement ingredients. He built it in the center of a ferrocement house that used bamboo for the reinforcement. Unfortunately, a heavy snow collapsed the roof and he died inside. Bamboo is not a good ingredient in ferrocement.

    One important variable in ferrocement is the ratio of metal to cement. Thin layers, and no gaps in the cement are critical. Chicken wire is less than ideal. The wide spacing, twisted junctions, and floppy nature complicate application of the cement without air pockets. Air pockets would be the demise of the shell in freeze thaw cycles. Since several layers of chicken wire are used, it becomes difficult to insure good penetration of the cement mix through the entire metal matrix.

    Expanded metal is more expensive, but less is needed. It is much easier to maintain quality control on the layers, and to insure good penetration. I use a cheap electric pad sander to vibrate the cement through the lathe. While it is razor sharp, it can be shaped quite easily, and if needed, 1/4 inch pencil rod makes good reinforcement for any imaginable shape. Depending on the size of the shell, the cost of the expanded metal would not be major. I think two layers would be more than adequate. I have made several single layer rock shapes without any pencil rod or rebar and they have done fine outside - no cracks at all. They are about 3/8" thick.

    Expanded metal and cement expand and contract at nearly identical rates in response to temperature change. This makes it strong through normal temperature ranges. Above 200 degrees, however, they no longer expand and contract at the same rate. The higher you go the worse it gets. This implies a stove shell would need to be insulated from the stove. I think Ken Kern used perlite because heat does not travel through it. Perhaps the cob, if thick enough, would provide the necessary insulation from the fire box, oven, and flue.

    There are other things you can do to make the ferrocement weather well. Air entrainment is one technique. A foam is added to the mortar during mixing and the air is trapped making the cement lighter, and giving better resistance to freeze/thaw. I have not tried this. It's a bit more technical than I am.

    good luck
    Gary
     
  5. Paul Wheaton

    Paul Wheaton Well-Known Member

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    Excellent info gobug!

    How many fc projects have you done?
     
  6. gobug

    gobug Well-Known Member Supporter

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    Paul
    Thank you.
    I have made half a dozen small table tops with the interest being a future 1/2 inch thick counter top, a 5x13 porch, a large water feature (16x16 failure), a prototype cistern (no metal) 1/8" thick 55 gallons, and a prototype 20 foot beam -- more study than production. I participated in spraying cement on an inflatable form in Oregon resulting in a 10 ft diameter 1/4 inch shell, and helped a professor build a 400 sq foot cement thin shell cement roof here in CO. I demonstrated his technique at the thin shell concrete conference in Oregon this year.

    There is a lot of research going on around the world on cement products -- rediscovering Roman secrets, and applying modern science. I like it because I don't need to be a scientist to experiment and have good results. I gave up on building a ferrocement house, because the code demons are not up to speed and it is too expensive to educate them.

    One of my plans, besides the counter tops, is garden boxes. I'm thinking it would be cheap and quick to make an 1/8 inch thick panel and attach small rocks (using cement of course) to make the sides. Fist sized rocks are more abundant and easier to handle. Plus the box walls would be much thinner.
     
  7. gobug

    gobug Well-Known Member Supporter

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    One other recent idea is a bottle wall using drywall mesh tape (no metal) to support the bottles. The wall would only be about 3/8" thick cement, so the bottles would protrude on both sides. I have been trying to get around to making this since I have a bag of Portland, a roll of mesh tape and a bunch of wine bottles. The mesh tape would be a matrix or cross hatched pattern between the bottles, with openings slightly smaller than each bottle. I need a form to set everything on, but once the cement sets up, it should be light enough to lift and place between posts with a slot in each post to hold the panel in place.
     
  8. Paul Wheaton

    Paul Wheaton Well-Known Member

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    Do you have pics of all this stuff?

    Have you considered making a web page?
     
  9. gobug

    gobug Well-Known Member Supporter

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    Paul
    The link I posted in the garden box thread contains photos from the construction of the 400 sq ft thin shell cement roof in a separate folder, and pictures of this years thin shell conference in yet another folder. This is the homepage that shows the folders:

    http://community.webshots.com/user/nogobug

    I don't have a web page, never figured out how to do that. I have tons of other photos. Some were posted on the above site, but I have removed many. It's tedious to load one photo at a time over a dial up connection, but if you're interested in something specific I could post a few or send them to you directly.

    I have many pictures of the water feature. The framework was made with 1/2 inch rebar and chicken wire. I consider it a failure and am in the process of disassembly. It was my first project, and too big. I didn't know enough about what I was doing. The disassembly has been an education in itself. I can clearly see where the structure is weak from the cement not getting thoroughly through the layers. A few areas were made later with expanded metal, and are much better. I used a small sprayer called a tyrolessa. ($200) It worked fine on the expanded metal because it didn't have to penetrate so far. The "mountain" as I call it, is the only project that I used the tyrolessa sprayer.

    Do you have other interests in "ferrocement" besides the cobb stove/oven?
     
  10. Old Jack

    Old Jack Truth Seeker

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    Hey Gobug how do you like your Tirolessa?
    I remember you saying you were getting one.
    It's still on my wish list.
     
  11. gobug

    gobug Well-Known Member Supporter

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    It is the cheapest cement sprayer you can get. It does a good job with a good home sized compressor (9cu ft/min or more). I suggest hiring someone to use it for you, or work out with weights for a long time before your project. You need gorilla arms. It will use cement as fast as you can mix it. I had one guy mixing dry material, one guy running the mortar mixer, two guys hauling buckets of mud and a sprayer. We kept changing around so the sprayer guy could take a break.

    It works alright while you're spraying at chest level or below. It gets more difficult as you move upward.

    The sprayer did not do well on several layers of chicken wire. It did fine, actually very fine on two layers of metal lathe. In taking down the "mountain" I found the cement only penetrated so far before it packed over and built up on the outside. So I don't recommend it for chicken wire armatures.

    We used a $60 ceiling texture sprayer to coat the inflated plastic form in Oregon. It took a lot longer because each layer was like 1/32 inch thick. But it still worked.

    Old Jack, aren't you the guy that put a gargoyle on top of your tire structure?
    Gary
     
  12. Old Jack

    Old Jack Truth Seeker

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    Thanks for the review Gary .
    Sounds like it will still do the job I need it for.
    Interesting about the chicken wire, I guess I'll have to rethink my 20 ft concrete gorilla project...
    Yes the gargoyle on the tire pillar is mine
     
  13. MELOC

    MELOC Master Of My Domain

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    Ken Kern wrote a book called "The Masonry Stove" and shows how to build a curvilinear ferrocement stove/oven. He used regular cement ingredients. He built it in the center of a ferrocement house that used bamboo for the reinforcement. Unfortunately, a heavy snow collapsed the roof and he died inside. Bamboo is not a good ingredient in ferrocement.

    I JUST FOUND THAT COMICAL...not that it is really funny. sometimes comedy is all abnout the delivery.