thin shell cement roof construction

Discussion in 'Shop Talk' started by gobug, Aug 6, 2004.

  1. gobug

    gobug Well-Known Member Supporter

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    I was lucky today. I got to help a man work on a thin shell hypar roof. His name is George Nez and he has built these roofs for more than 20 years. It helps me to retain information if I report what I learned. So I'm reporting to you. The
    following are today's notes.

    Construction of the thin shell hypar in Boulder had already begun when I
    arrived this morning at 10. George Nez and a guy I didn't meet yet, built the
    frames for four connected hypars on Wednesday and Thursday. They used salvage
    lumber. They built two separate halves to allow transport by truck to the
    University. These halves will be joined and additional cement applied to connect them
    when they are in place on the support walls. There is no electricity on the
    site, so a hammer, square, and hand saw were the tools used to build the
    framework.

    The hypars form a square 20 feet on a side with a 10 foot high peak in the
    middle. Shortly after I arrived, George's helper left. That left just George and
    I to apply the fabric. He bought AR glass (3 rolls at 34.5"x600' for $400
    including shipping) He says this works out to about $0.25 per square foot when
    overlapped. I asked about fiberglass degrading in cement and he said that using
    the acrylic without water in the slurry protects the fiberglass. The acrylic
    needs to have 25% solids. I remember Herb N. saying that solid content in the
    acrylic is very important. George has been building these now for more than 20
    years without a failure. The process of attaching the fabric is the most
    important part of building one of these structures. It must be taut, without
    wrinkles. The process of attaching the fabric creates the curves that create both
    tension and compression. Just like ferrocement, air gaps cause failure. The
    frame must be rigid during the application of the fabric. Some tensioning
    structural members are removed after assembly.

    The screen is attached first to the flat corner (two connecting sides set
    flat, two sides rise 10 feet). We started with 18 inch strips, but that was too
    wide and was difficult to get taut. We removed the 18 inch strips and cut the
    rest of the material to 12 inches. The smaller strips were much easier to line
    up and tension. Since the hypar rises 10 feet, the length of the strips
    gradually increases as you work up the rise. Each strip was started on the flat side
    of the frame and stapled square to the frame. Then the other end was pulled
    tight. We slightly angled the strip on the rise to compensate for the longer
    length. We used staplers and razor knives for this part.

    With two of us working about 3 hours we nearly finished attaching one-fourth
    of the fabric. If the fabric had been already cut to size we could have easily
    finished one-fourth in about 2 hours. Tomorrow there should be several
    helpers and George thinks we may get to applying the cement slurry.

    I will post pictures as soon as I find my camera cable.
    Gary
     
  2. gobug

    gobug Well-Known Member Supporter

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  3. gobug

    gobug Well-Known Member Supporter

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    Another day and a half of labor has finished the application of fabric to the frame of the hypar. The fourth hypar took 3 guys less than 3 hours. I have one arm in a sling and George is about 70 years young. George estimates that 3 healthy guys could do the four hypar assembly in a day and a half. I took more photos and have posted them:

    http://community.webshots.com/album/172344866YPtYmD

    http://community.webshots.com/album/172969403ZfWFsE

    We will begin putting cement on the fabric late this week. It will take several days. Each day a thin coat will be applied. It won't take all day, but it must dry for a day to avoid distorting the fabric shape.

    Gobug
     
  4. ed/IL

    ed/IL Well-Known Member

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    Good info. Keep posting updates Thanks.
     
  5. BrushBuster

    BrushBuster Well-Known Member

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    yes! very interesting. i've been around alot of construction, but thats a new 1 on me. keep posting. can't wait to see the finished product.
     
  6. gobug

    gobug Well-Known Member Supporter

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    Today we started putting cement on the hypar structure. We didn't use electricity, just hand tools. We finished half of the roof with 4 people. Only one had ever done this before, George Nez.

    Check out the photos:

    http://community.webshots.com/album/174447416lROsha

    Gobug
     
  7. gobug

    gobug Well-Known Member Supporter

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    I have posted more pictures of the hypars. The initial cement coats are finished and the structures must now be moved to the campus. Once they are moved, they will be joined together and another two coats of cement will be applied. Then the roof will be raised onto supports and walls will be built beneath.

    I plan to photograph every step.

    Here's the link, the pictures are in the folders at the bottom of the page, and titled as Nez roof day X:

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